Covid-19: Some U.S. Vaccination Sites Will Close as Demand Drops

Some county health departments that couldn’t keep up with vaccine demand a month ago have now started closing some of their mass vaccination sites for lack of customers, and some counties are declining vaccine shipments.

Now that more than half of adults in the United States have received at least one Covid-19 vaccine dose and the country has surpassed 200 million administered doses, demand for shots appears to be slowing in many areas.

White House and health officials are comparing the next phase of the vaccination campaign to a get-out-the-vote effort. Officials in many states are looking beyond mass vaccination sites and focusing on having patients vaccinated at their doctors’ offices, where they are more at ease — a shift that will require the Biden administration to ship vaccines in much smaller quantities.

The seven-day average of vaccinations has declined somewhat in recent days, to 2.86 million doses a day as of Friday, from a high point of 3.38 million last week, according to a New York Times analysis of data from the Centers for Disease Control and Prevention.

What is emerging is an unequal landscape in which some places have more supply than demand and others have more demand than supply. In Seattle, for example, more than 200,000 people are on a waiting list for vaccines at city-run sites. Local officials have requested and are now receiving additional doses through a federal program.

At a news conference on Friday, Jeffrey D. Zients, the White House’s Covid-19 response coordinator, acknowledged that the pace of vaccinations nationally would ebb. “We expect daily vaccination rates will moderate and fluctuate. We’ve gotten vaccinations to the most at risk and those most eager to get vaccinated as quickly as possible,” he said. “And we will continue those efforts, but we know reaching other populations will take time and focus.”

Mr. Zients said two new federally run vaccination sites would open Friday in Kentucky, with a combined capacity of 7,000 shots each week.

Even with persistent vaccine hesitancy, the reasons for the dip in vaccination rates are still not entirely clear. Injections of Johnson & Johnson’s vaccine were halted last week as federal health officials investigated a potential rare side effect, and this may have had some effect on daily tallies, with millions of doses now sitting on shelves and yet to be allocated. On Friday, a panel of C.D.C. advisers recommended lifting the pause on the vaccine for all adults and adding a label about an exceedingly uncommon, but potentially dangerous, blood clotting disorder.

While every person 16 and older in the country became eligible for a coronavirus vaccination on Monday, falling demand has pushed Mercer County, Ohio — where 27 percent of adults have at least one dose — to announce the closing of its mass vaccination site on May 7.

In the first few months of the year, the site in the county, which has 41,000 residents and borders Indiana, would fill up its 400 appointments in an hour or two, said Jason Menchhofer, the county health administrator. But demand has fallen precipitously in the last several weeks, and last week the county ended up wasting two doses, which was a first.

“We no longer have a reserve of people who want to be vaccinated to reach into to show up and take those doses,” Mr. Menchhofer said.Officials in Palm Beach County, Fla., said that the county would shut its three mass vaccination sites, which are operating at about half capacity, by the end of May. Of 16,000 appointment slots available this week, only 6,000 were filled, according to health officials. Instead, three mobile units will each aim to give 500 doses a day.

In Galveston County, Texas, a mass drive-through clinic at a county park won’t operate after May 1. The park has been administering 5,000 doses per day, including on Thursday. But demand for appointments has dampened in the last three weeks, according to the county’s chief public health officer, Dr. Philip Keiser. He also asked the state to pause vaccine shipments.

“We’re concerned that some of it may expire before we use it, if we keep getting it,” Dr. Keiser said.

There will be much more targeted outreach, down to the census tract level, Dr. Keiser said, and there might be 100 or 200 injections per day rather than thousands.

“We got about 50 percent of our people vaccinated,” he said, “and we recognize that next 25 percent is going to be a lot harder than the first.”

The Food and Drug Administration ended its recommended pause on the Johnson & Johnson Covid-19 vaccine on Friday and will add a warning to its label to note the potential risk of rare blood clots.

The decision, which clears the way for states to resume vaccinations, came after a panel of advisers to the Centers for Disease Control and Prevention voted to end the pause in a meeting on Friday.

The shot could be deployed again by Saturday morning, Dr. Peter Marks, the F.D.A.’s top vaccine regulator, said at a news conference Friday evening.

Johnson & Johnson injections ground to a halt last week in the United States and Europe after reports emerged of a rare blood clotting disorder in six women who had received the vaccine. Nine additional cases have been confirmed since then, all in women. Three women have died from the rare clots and seven remain hospitalized, four of whom are in the intensive care unit.

The European Union resumed its rollout on Tuesday after Johnson & Johnson added a warning label to the shots. The F.D.A. on Friday released updated fact sheets that accompany the agency’s emergency use authorization, which officials said would reach physicians and the public by the time they get the shot.

In a warning to recipients of the vaccine, the F.D.A. noted that most of those who developed the rare clots were women between the ages of 18 and 49, and that the “chance of having this occur is remote.”

At the meeting, Dr. Tom Shimabukuro, the deputy director of the C.D.C.’s immunization safety office, presented the nine new confirmed cases, which brings the total to 15. All the cases have been in women, and 13 have been in women between 18 and 49 years old. The disorder combines blood clots, often in the brain, and a low level of platelets, blood cells that typically promote clotting.

The clotting disorder is “rare but clinically serious,” Dr. Shimabukuro said at the meeting.

The overall risk of developing the clotting disorder is extremely low. Women between 30 and 39 appear to be at greatest risk, with 11.8 cases per million doses given. There have been 7 cases per million doses among women between 18 and 49.

Dr. Rochelle P. Walensky, the C.D.C. director, said the government planned to emphasize the safety and effectiveness of the vaccine to doctors and Americans who might be hesitant to take it after the pause.

She said the C.D.C. had talked to health providers for young women, including the American College of Obstetricians and Gynecologists. The pause and investigation into the rare disorder, she added, should give the public confidence in the system used to monitor vaccine safety.

Nearly 8 million doses of the Johnson & Johnson vaccine have now been administered. Among men and women who are 50 or over, there has been less than one case per million doses.

Roughly 10 million doses or more of the Johnson & Johnson vaccine, produced at the company’s factory in the Netherlands, are sitting on shelves across the United States and could be deployed immediately. Several states, including Texas, Alabama, Utah and Wisconsin, said they expected to follow the recommendations of the C.D.C. and F.D.A. once the decision was made.

Dr. Walensky said that she heard intense interest from governors about resuming use of the shot.

“They wondered why we had paused and they were anxious to have this back, have an opportunity for a single-dose vaccine, for a one-and-done possibility,” she said.

The vaccine has immense potential benefits. If vaccinations resume for all adults, 26 to 45 cases of the clotting disorder would be expected over the next six months, according to a model that Dr. Sara Oliver, a C.D.C. scientist, presented at Friday’s meeting. However, 600 to 1,400 fewer Covid-19 related deaths would be expected over the same time period.

The vaccine, which is easy to store and requires just one shot, is also especially well-suited for use in hard-to-reach populations, including people who are homebound, homeless, or incarcerated.

Additional potential cases of the clotting disorder, including some in men, are currently being reviewed. Dr. Shimabukuro also mentioned one case that developed in a 25-year-old man who participated in a clinical trial of the vaccine.

Twelve of the 15 women in the confirmed cases developed blood clots in the brain. Many also had clots elsewhere. Initial symptoms, which include headaches, typically begin six or more days after vaccination, Dr. Shimabukuro said. As the disorder develops, it can cause more severe headaches, nausea and vomiting, abdominal pain, weakness on one side of the body, speech difficulties, loss of consciousness and seizures.

Dr. Shimabukuro noted that seven of the women were obese, two had hypothyroidism, two had high blood pressure, and two were using oral contraceptives. It is not yet clear whether any of these factors might increase the risk of developing the clotting disorder after vaccination.

The patients’ symptoms closely resemble a rare syndrome that can be caused by heparin, a widely used blood thinner, Dr. Michael Streiff, a hematologist at Johns Hopkins University, told the panel. Heparin, which might typically be used to treat blood clots, should not be used to treat these patients, he said.

Doctors should consider the rare clotting disorder if patients develop blood clots and low levels of platelets within three weeks of receiving the Johnson & Johnson vaccine, Dr. Streiff said.

“Recognition that this syndrome exists is helping to improve outcomes,” he said.

The F.D.A.’s decision comes as the federal government is also investigating problems at a Baltimore factory that was slated to help satisfy the country’s vaccine demand. Emergent BioSolutions, the plant’s operator, has produced tens of millions of doses of Johnson & Johnson’s vaccine, but they cannot be distributed until regulators certify the plant.

After Emergent had to discard up to 15 million possibly contaminated doses of the vaccine last month, federal regulators conducted an inspection that found a series of problems, including the risk that other batches could have been contaminated.

With the decision by the Food and Drug Administration on Friday to lift its recommended pause on administration of the Johnson & Johnson vaccine, many states are likely to start using it again in short order.

Several states, including Texas, Arizona, Alabama, Utah and Wisconsin, had said they expected to follow the recommendations of the F.D.A. and the Centers for Disease Control and Prevention once the decision was made. (The F.D.A. issued its new guidance after advisers to the C.D.C. voted to lift the pause.) Other states, including Washington State, had said they would wait until the conclusion of the C.D.C. meeting and then formulate their plans.

Dr. Karen Landers of the Alabama Department of Public Health said the state would “follow the guidance of the committee and C.D.C. if there is guidance to resume use of Johnson & Johnson.”

Shelby Anderson, a spokeswoman for the Washington State Department of Health, said the Western States Scientific Safety Review Workgroup was scheduled to convene after the C.D.C. meeting. “Right now, it’s too soon to say when a decision could be made,” she said.

Elizabeth Goodsitt, a spokeswoman for the Wisconsin Department of Health Services, said that the state would follow the federal recommendation, and that its plan was to allocate doses of the Johnson & Johnson vaccine primarily “to local health departments, as well as smaller providers, to offset the hub deliveries and storage challenges of Pfizer.”

In a statement, the Minnesota Department of Health said the vote “underscores the importance that is placed on vaccine safety.”

Just before the rollout was halted last week, Minnesota had distributed 9,600 Johnson & Johnson doses to providers, officials said, adding, “Those doses have been stored by the providers who received them, and we expect them to be available in the coming days along with any updated information to provide to those getting the vaccine.”

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India Faces Record-Breaking Virus Surge

India set a global record for new daily coronavirus infections on Friday, beating the previous record from the day before, while oxygen supplies dwindled.

The situation right now here is really, really worst, critical and out of control. The staff is really cooperative, but due to the overcrowding, all through the main hall of the walk-in casualty, it is difficult to provide equal treatment to all the patients. That’s why there is a highly casualty rate inside, and there’s a very negative environment inside. The situation in India is a devastating reminder of what this virus can do and why we must marshal every tool against it in a comprehensive and integrated approach. This is a scenario that’s playing out around the world and will continue to play out unless we ensure equitable access to the tools needed to save lives. The solution is straightforward. We need countries and companies that control the resources that could save lives to share.

The Times’s Emily Schmall reports from New Delhi on the desperate situation in India. The following is an excerpt from her article.

NEW DELHI — A catastrophic second wave of the coronavirus is battering India, which is reporting the world’s highest number of new infections as hospitals and patients beg for fast-diminishing oxygen supplies and other emergency aid.

India recorded more than 330,000 coronavirus cases in 24 hours, the health ministry said on Friday, the second consecutive day that the country has set a global record for daily infections.

Canada has joined Britain, Hong Kong, Singapore and New Zealand in barring travelers coming from India. And the U.S. State Department advised people against going to India after the Centers for Disease Control raised the risk level to its highest measure.

Even as cases have climbed, Prime Minister Narendra Modi’s governing Bharatiya Janata Party and other parties have continued to hold mass rallies with thousands of people unmasked. The government has also allowed an enormous Hindu festival to draw millions of pilgrims despite signs that it has become a superspreader event.

The catastrophe in India is playing out vividly on social media, with Twitter feeds and WhatsApp groups broadcasting hospitals’ pleas for oxygen and medicines, and families’ desperate searches for beds in overwhelmed Covid-19 wards. With many hospitals short of ventilators, television reports have shown patients lying inside ambulances parked outside emergency rooms, struggling to breathe.

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New York Allows Walk-Ins at All City-Run Vaccination Sites

Mayor Bill de Blasio of New York announced on Friday that all eligible residents could now get vaccinated for Covid-19 at any city-run site without an appointment.

All city-run sites, as of now, will be open to all New Yorkers, regardless of any geographic restrictions that existed previously. We want to make it simple. You can go to any city-run site — Health and Hospitals, Department of Health, any site — you can go there and get a shot. Doesn’t matter where you live. Second, all city-run sites will be open for walk-ins as of today, for all sites, for all age levels. So you can just walk up and get vaccinated. If you’re 16 years old or older for the sites using Pfizer, 18 years old and older at the sites using Moderna. We did a walk-up pilot project focusing on the oldest New Yorkers. We saw really good results. A lot of people said it was the reason they came and got vaccinated, that it was a lot simpler for them. And we did not have the kinds of lines we were worried about that might be a problem. So we’re quite confident we could accommodate a much higher volume of walk-ins. So we’re going to make that universal at all the city-run sites, again, for all ages.

New York City is now allowing any eligible New Yorker to get vaccinated at city-run sites without an appointment, an attempt to simplify the inoculation process and expand access, Mayor Bill de Blasio said on Friday.

“We want to make it simple,” Mr. de Blasio said at a news conference. “We want to encourage people. And let’s face it, convenience matters to New Yorkers.”

The city had begun allowing walk-in vaccinations for people older than 50 last week. Friday’s expansion to all eligible New Yorkers is limited to sites run by the city’s health department and its public hospital system, but as of Friday, New York State has also begun allowing walk-in vaccinations to anyone older than 60 at 16 of its vaccination sites, including five in New York City.

Being able to walk into a vaccine site will simplify a process that had confounded many New Yorkers desperately seeking vaccines. Appointments at all vaccination sites, including those run by the city, were elusive for months. New Yorkers often had to check dozens of websites, each with a different sign-up protocol. In some cases, appointments seemed to disappear as residents were trying to book them.

Officials had long worried that navigating the complex system was a major barrier to the equitable distribution of the vaccines in New York.

As the supply of vaccines increased, appointments became far less scarce. Mr. de Blasio said that the city was now confident enough in its continued supply to eliminate the need for appointments.

Mr. de Blasio also said the city was eliminating rules that had restricted appointments to residents of neighborhoods surrounding certain sites.

The requirements were initially meant to address inequitable distribution of the vaccine and ensure that residents in harder-hit neighborhoods or boroughs had access.

As of Friday, more than six million doses have been administered in New York City. According to the city’s data, 50 percent of residents over 18 have received at least one dose.

But inequity remains: 60 percent of eligible adults have received one dose of the vaccine in Manhattan, compared with 41 percent in the Bronx and 45 percent in Brooklyn.

Black and Latino residents are also being vaccinated at a slower pace than white residents. Of the city residents who had received one dose and whose race was recorded, about 34 percent were white, 21 percent were Asian, 20 percent were Latino and 13 percent were Black. The city’s population is roughly 29 percent Latino and 24 percent Black.

The new walk-in policy does not expand eligibility requirements for the vaccine: Only those ages 16 and older can receive the Pfizer-BioNTech vaccine, and only those 18 and older can receive the Moderna vaccine.

Mr. de Blasio said the city was pressing community health centers to adopt similar policies. Officials were also urging private doctors to call their patients and urge them to get vaccinated.

For weeks, Illinois has been beset by a stubbornly high daily load of reported coronavirus cases, leading to climbing hospitalizations and deaths. But new data is signaling that the virus might be on the verge of retreat.

Illinois is reporting an average of about 2,900 new cases a day, down nearly 13 percent from a week ago. Central Illinois, which saw major growth in cases earlier this month, is now improving, according to a New York Times database — especially in Peoria, one of the metropolitan areas where the virus had been spreading the fastest.

“It is great we have seen some abatement in local hot spots,” said Dr. Emily Landon, the chief epidemiologist at the University of Chicago, who has been advising Gov. J.B. Pritzker on the state’s pandemic response. Dr. Landon cautioned that there were other pockets of the state, though, especially those with low vaccine rates, that remain ripe for “a fiery outbreak.”

“I wouldn’t say everybody is out of the woods,” she added.

Illinois’s latest surge in cases followed the rising trends in other Midwest states like Michigan and Minnesota beginning in late February and March. The situation grew particularly worrisome in Michigan, which continues to lead the nation in cases per 100,000 per people, but has seen a 15 percent decline over the past two weeks.

The case counts surged at a time when variants were starting to spread widely, and states have been racing to vaccinate as many people as possible, in part to head off the variants. About a quarter of Illinois’s population is now fully vaccinated, and 43 percent of residents have received as least one shot. Officials said the recent surge may be burning itself out in part because of the growing number of people who are protected.

“We have seen a beginning, of maybe a lessening of the rise of cases,” Governor Pritzker said last week. “I don’t want to predict anything, because this virus is unpredictable. But I think at least in the short term, that seems to be good news.”

In Central Illinois, Peoria County reported new-case declines of about 23 percent from two weeks ago. Local officials said that when vaccinations first became widely available, people started taking fewer precautions, even though highly contagious variants were spreading.

“It led to the perfect storm,” said Monica Hendrickson, public health administrator for the Peoria City/County Health Department.

Hospitalizations and Covid deaths remain high in Illinois, putting mounting pressure on the health care system. Hospitalizations are up by about 29 percent over the past two weeks, and deaths have risen by 15 percent during that period, according to Times data.

Dr. Michael Cruz, chief operating officer at OSF HealthCare, said on Thursday that about a half-dozen of the hospital system’s medical centers in Illinois are at more than 90 percent of capacity. He said it was too early to say whether the recent decline in new case reports was a “true inflection point.”

“The virus does what the virus does,” Dr. Cruz said. “Let it hang around long enough, it will start mutating.”

SAN JUAN, P.R. — Throughout the pandemic, Dr. Víctor Ramos, a pediatrician, had not seen more than two Covid-19 patients hospitalized at the same time at San Jorge Children & Women’s Hospital in San Juan, the Puerto Rican capital, where he works nights. When he left after one of his shifts a few days ago, the hospital’s pediatric patient count had grown to 10.

“We had never seen that,” he said.

Puerto Rico has experienced its worst coronavirus outbreak of the pandemic over the past five weeks, with an explosive growth in cases exceeding records that had been set in December. Only this week did the numbers stop rising, giving the territory its first respite since the surge began in mid-March.

Behind the rise, experts say, was a confluence of factors, including the arrival of variants that probably made the virus more contagious right when people weary of staying home and hopeful about vaccines began to let their guard down, returning to work in person and shopping and dining indoors. Tourists poured in for spring break season. People gathered to celebrate Holy Week, a time when many are off work.

“The government relaxed restrictions around January and February — it opened the economy completely,” said Mayor Luis Javier Hernández Ortiz of Villalba, a town in south-central Puerto Rico. “This gave the virus opportunities to spread that it didn’t have a year ago.”

In early April, the island went from averaging about 200 new cases a day to about 800, according to a New York Times database. In the week leading up to April 13, more than 7,100 cases were identified, a record. In a two-week period this month, cases rose by 151 percent.

AstraZeneca, which shipped millions of doses of its coronavirus vaccine to Mexico and Canada last month at the direction of the Biden administration, said on Thursday that the doses had been made at a Baltimore plant where production was halted because of serious manufacturing flaws.

AstraZeneca’s vaccine, made until recently by Emergent BioSolutions in Baltimore, is not authorized for use in the United States, and tens of millions of doses have been sitting idly at manufacturing plants. But the White House said last month that the federal government, which committed last year to buying 300 million doses from the company, intended to “loan” 2.5 million doses to Mexico and 1.5 million doses to Canada.

Whether regulators from those countries inspected the Emergent plant before accepting the AstraZeneca doses, and whether American officials warned them of the ongoing issues at the site, is unclear.

The New York Times reported this month that from early October to January, Emergent discarded five lots of the AstraZeneca vaccine — each the equivalent of two million to three million doses — because of contamination or suspected contamination, according to internal logs, a government official and a former company supervisor.

Rail-thin teenagers holding placards at traffic stops with fome — the word for hunger — in large print. Children begging for food outside supermarkets. Families huddling in flimsy encampments on sidewalks, asking for baby formula, crackers, anything.

The scenes of hunger in Brazil are stark evidence that President Jair Bolsonaro’s bet that he could protect the country’s economy by resisting public health policies intended to curb the virus has failed. From the start of the pandemic, he scorned the guidance of health experts, arguing that the economic damage wrought by lockdowns would be a bigger threat to the economy than the coronavirus itself.

That trade-off led to one of the world’s highest death tolls, but it has not kept the country afloat.

About 19 million people have gone hungry over the past year, and about 117 million people — more than half the country — faced food insecurity, with uncertain access to enough nutrition, in 2020, according to estimates. One expert says: “The way the government has handled the virus has deepened poverty and inequality. Hunger is a serious and intractable problem in Brazil.”

Most adults who test positive for the virus that causes Covid-19 don’t require hospital care, but they tend to seek medical care in the following months, and two-thirds of those who do seek care receive a diagnosis of a new health condition they did not have previously, a new study reports.

The study, conducted by investigators from the Centers for Disease Control and Prevention and Kaiser Permanente, included some 3,171 members of the Kaiser Permanente Georgia integrated health care system. More than half were Black.

The message for patients is that even for those who have had only mild Covid-19, “it’s possible you may experience new or persistent symptoms months after the initial diagnosis,” said Dr. Alfonso C. Hernandez-Romieu, an infectious disease specialist with the C.D.C. who was the study’s lead author. “And it’s important for people to make sure they’re going to their clinicians,” he said, to express their concerns.

“It’s equally important,” he added, “for clinicians to acknowledge that there may be these long-term effects and to really make sure they’re validating patients, treating them with empathy and trying to help them in the best way possible.”

Clinicians need to monitor patients for Covid-19-related complications that are potentially very serious, like blood clots, he said.

The study did not compare patients who tested positive for the coronavirus to patients who did not test positive, so the authors were unable to say whether people who had recovered from mild Covid-19 cases made more doctors’ visits than those who never had the virus.

But two-thirds of the patients who had mild disease sought medical care a month to six months after their Covid-19 diagnoses, and about two-thirds of those who sought care were found to have an entirely new condition. The new diagnoses included cough, shortness of breath, heart rate abnormalities, chest or throat pain, and fatigue, “which likely represent ongoing Covid-19 symptoms,” the study said.

Among those more likely to seek medical care were adults 50 and older, women and those with underlying health conditions. Black adults were also slightly more likely than others to seek care. But over all, the authors noted, the number of visits declined over time.

The potential for long-term complications, even after a mild course of disease, underscores the need for prevention measures and vaccination, Dr. Hernandez-Romieu said.

“There is a lot we don’t know about post-Covid conditions,” he said. “Even though a majority of people don’t end up with severe Covid, or end up in the hospital, the potential for long-term health effects is really important.”

A panel of advisers to the Centers for Disease Control and Prevention has recommended lifting the pause on the Johnson & Johnson Covid-19 vaccine for all adults while adding a warning label about a rare but dangerous blood clotting disorder. But a central mystery persists: How might a vaccine that has been given to nearly eight million people cause the side effect in just a few of them?

There’s no clear answer yet, but Dr. Andreas Greinacher, a researcher at University Medicine Greifswald in Germany, is leading one effort to find out. At a news conference on Tuesday, he said that he had reached an agreement with Johnson & Johnson to inspect the components of the vaccine to see if it could disrupt the normal blood clotting process under certain rare conditions.

“We just agreed that we would like to work together,” he said.

It’s possible, Dr. Greinacher said, that the Johnson & Johnson vaccine can cause rare side effects by the same process that he suspects is responsible for similar side effects from the AstraZeneca vaccine. The main ingredient in both vaccines are harmless viruses known as adenoviruses, which slip into human cells and deliver a coronavirus gene that will later cause an immune response.

On Tuesday, Dr. Greinacher and his colleagues released a report on how the AstraZeneca vaccines might trigger the side effect. The study has not yet been published in a scientific journal.

The scientists found that components in the AstraZeneca vaccine could stick to a protein that platelets release during the formation of blood clots. These clumps of molecules could be seen by the body as foreign invaders, the scientists speculated, triggering a cascade of reactions that cause platelets to turn into dangerous clots.

Dr. Paul A. Offit, a vaccine expert at Children’s Hospital of Philadelphia who was not involved in the study, found Dr. Greinacher’s study intriguing but far from the final word. “He throws out a lot of possibilities,” he said.

Dr. Offit said it was not clear which of the many factors the researchers studied might explain the rare blood clots in people vaccinated with AstraZeneca’s doses. “It’s like sipping from a fire hose,” he said.

At a news conference on Tuesday, Dr. Greinacher said that the research might point to ways, in the AstraZeneca vaccine, of lowering the risk of the clots or treating the side effects. But he emphasized that the small risk of those side effects was strongly outweighed by the protection that vaccines such as AstraZeneca’s provide against Covid-19.

“Not being vaccinated is far more dangerous than being vaccinated and at risk for this adverse drug reaction,” he said.

Antonia Laraki has a leg badly swollen from lymphedema and a son with autism at home who relies on her. After applying for a citywide program in mid-March that vaccinates homebound people, she waited weeks just to hear when the city might be able to send someone to her apartment.

Finally, on Tuesday, she got the news: Vaccinators would be able to make it to her apartment the next day, with the Moderna shot. The city had been using Johnson & Johnson for the program, but after a pause in administering that vaccine because of a rare blood clot disorder, some of its partners were able to pivot.

Still, the pause caused the cancellation of over 1,000 appointments for homebound people, adding yet another hurdle to a program that has moved slowly.

“I feel relieved,” Mrs. Laraki, 75, said on Friday from her apartment in a Manhattan housing project.

While more than two million people are now fully vaccinated in New York City, the city’s effort to vaccinate homebound seniors has lagged. Though there are an estimated 23,000 homebound adults who need shots, city teams had made only 3,600 vaccination visits as of last week.

The city did not begin its main homebound vaccine effort until March 1, in large part out of a desire to wait for the Johnson & Johnson vaccine, which is logistically easier to use because it requires just one dose. The unexpected pause, and lingering fear generated by it, could be a major setback to the program, which had finally ramped up and was reaching about 1,200 people per week.

A committee of health experts met on Friday and recommended that federal officials lift the pause.

“We are in a time frame here that is frightening,” said Gale Brewer, the Manhattan borough president and leader of a weekly task force meeting focused on the vaccine rollout. “We are all trying to beat the variants, and with the home health aides going in and out, there is risk.”

After a year in which many people have learned to dutifully wear masks and look askance at anyone who does not, it’s understandable that people remain fearful when they cross paths with the unmasked. So how to decide about when to wear a mask outside?

Many experts in viruses and public health say the guidance hasn’t changed: Spending time with others outside during the pandemic has always been safer than indoors. But whether a mask is needed outdoors depends on the circumstances, including local public health rules and whether people are vaccinated.

On Thursday, Dr. Rochelle Walensky, director of the Centers for Disease Control and Prevention, said on the “Today” show that the agency is considering revising its mask guidance for outdoor activities as more and more people get vaccinated against the coronavirus.

“We will be looking at the outdoor masking question,” she said. “But it’s also in the context of the fact that we still have people who are dying of Covid.”

She added that if “we can get our caseloads down, then we’ll be in really good shape in the country.”

While new cases, hospitalizations and new deaths have declined from their peaks in January, they have stayed at a relatively stagnant level in recent weeks, according to a New York Times database. The average of new cases is more than 61,000 a day, as of Thursday, with high concentrations in Michigan and the Northeast. And new deaths remain near an average of more than 715 a day.

Currently, the C.D.C. says masks “may not be necessary” when you are outside by yourself away from others, or with people in your household, but it does not explicitly say there is no longer a need to mask up while outdoors.

Brief encounters with an unmasked person on a sidewalk or a hiking trail are very low risk, said Linsey Marr, a professor of civil and environmental engineering at Virginia Tech who is one of the world’s leading experts on viral transmission.

Even if a person coughs or sneezes outside, the odds of someone nearby getting a large enough dose of virus to become infected remain low, she said.

Dr. Marr uses a two-out-of-three rule for deciding when to wear a mask in public spaces or when she doesn’t know others’ vaccination status. In these situations, she makes sure to meet two out of three conditions: outdoors, distanced and masked.

“If you’re outdoors, you either need to be distanced or masked,” she said. “If you’re not outdoors, you need to be distanced and masked. This is how I’ve been living for the past year.”

Dozens of inmates at an Iowa prison were sickened this week after the prison’s nurses inadvertently administered overdoses of the Pfizer coronavirus vaccine, an error medical experts fear could erode trust among a population already wary of vaccinations.

At least 77 inmates at the Iowa State Penitentiary in Fort Madison received shots on Tuesday that contained six times the recommended dosage. The Iowa Department of Corrections said that it had temporarily halted administration of the vaccine at the facility and that two nurses had been placed on administrative leave pending an investigation.

Cord Overton, a prison spokesman, said that none of the inmates had been hospitalized, but that they were suffering from ailments consistent with people who have had adverse reactions to the vaccine, including body aches and low-grade fever.

While prison inmates in most states have begun to receive vaccinations, the hesitancy rate among both incarcerated people and prison guards is a concern for public health officials. In Pennsylvania, for example, as many as 75 percent of correctional staff and 45 percent of inmates have not yet been inoculated, despite the availability of the vaccine.

Public health experts fear that given the reluctance to get inoculated, outbreaks in correctional facilities might continue well after much of the rest of society has been vaccinated, creating islands of infection.

Jaimie Meyer, an associate professor at the Yale School of Medicine, said dosing errors involving the Pfizer vaccine had been “rare.” She said that medical care at prisons presented particular problems because of inadequate staffing.

“When there’s a single nurse practitioner who’s meant to take care of a thousand patients, they often don’t have the same levels of support that you would elsewhere,” Dr. Meyer said.

In Iowa, the Corrections Department said its nurses had been told to follow the instructions on the medication when preparing the doses and to consult a statement on proper procedures from the manufacturer.

In a sweeping move likely to be followed by campuses across the nation, the University of California and California State University systems — two of the country’s largest public university systems — are planning to require Covid-19 vaccinations by the start of the fall semester for all students, faculty and staff.

The proposed mandate, contingent on full approval of one or more vaccines by the Food and Drug Administration, comes as a growing number of private universities — including Stanford, Duke, Brown, Cornell, Syracuse and Rutgers — have announced similar conditions for returning to campus or attending in-person classes.

The decision in California, however, will affect roughly one million people in college towns and campus environments that served as hotbeds for the spread of the virus last year. The 10 U.C. and 23 California State campuses collectively enroll more than 764,000 students and are among the largest local employers in many parts of the state.

In recent months, California has brought its rate of new Covid-19 cases down from one of the nation’s highest to one of the lowest. University officials said that they were making the announcement now so students and employees could plan, and that students who opted out would be required to obtain medical exemptions and could be denied campus housing.

“Receiving a vaccine for the virus that causes Covid-19 is a key step people can take to protect themselves, their friends and family, and our campus communities while helping bring the pandemic to an end,” the University of California president, Michael V. Drake, who is also a physician, said in a statement.

The California announcement was quickly followed by similar mandates from the University of Massachusetts-Amherst and from Maryland’s public university system. And on Friday, the University of Michigan said it would require all students who chose to live on its Ann Arbor campus during the fall to be fully vaccinated for the coronavirus.

“We know that widespread vaccination will be the only way to facilitate a return to normal and robust campus life,” Martino Harmon, the University of Michigan vice president for student life, said in an announcement. “This is not a mandate to be vaccinated, but rather a choice to live in communal living and therefore make the choice to get vaccinated.”

Vaccine requirements for communicable diseases such as polio, diphtheria and whooping cough are already in place at most colleges and universities.

With summer on the horizon, states are beginning to rethink social-distancing measures.

In Rhode Island, Gov. Dan McKee said that starting May 7, the state will stop requiring masks outside, and social gatherings can increase to 25 people indoors and 75 people outdoors. By May 28, the state will lift capacity limits on businesses and houses of worship, the bar areas of restaurants will be able to open, and dance floors can once again be filled.

“It’s a good day for everyone here in the Ocean State,” Mr. McKee said at a news conference on Thursday. “It’s a little early to put a ‘Mission Accomplished’ sign up, but we’re getting ready to order that sign.”

Mr. McKee attributed the reopening plans to the state’s vaccination rate — 48 percent of residents have received at least one shot, and 33 percent are fully vaccinated, according to a New York Times database. But masks will still be required indoors.

Rhode Island is not alone.

On Monday, Gov. Ned Lamont of Connecticut said that the state would phase out all pandemic restrictions, except the indoor mask mandate, by May 19. And in New Jersey, Gov. Phil Murphy said on Wednesday that he would announce “a pretty significant amount of guidance” for summer activities next week.

“We don’t want to lurch, in other words go forward and then have to pull something back,” Mr. Murphy said at his weekly news conference. “And we don’t want to start that now. But we also owe people our best guesses for what it’s going to look like for graduation, summer, the beaches and what not.”

As more people get vaccinated and the outdoors become more appealing with spring weather and sunshine, one question persists: Do people still need to wear masks outside? Science shows that the risk of viral transmission outside is very low. The Times’s Well columnist, Tara Parker-Pope, suggests making sure activities meet two out of the following three conditions: outdoors, distanced and masked.

Dr. Rochelle Walensky, the director of the Centers for Disease Control and Prevention, said on Thursday that the agency was “looking at the outdoor masking question” and whether to revise current guidance.