Vaccinated People Can Get Covid, but It’s Most Likely Very Rare

More than two months after being fully vaccinated against Covid, a doctor in New York awoke with a headache and a dull, heavy feeling of tiredness. Fever and chills soon followed, and his senses of taste and smell began to fade.

That, he thought, couldn’t happen. But it was: He tested positive for the corona virus.

“It was a big shock,” he said. He knew that no vaccine was perfect and that the Pfizer BioNTech shots he received were 95 percent effective in a large clinical trial. “But somehow it was 100 percent in my eyes,” he said.

The doctor, who asked for anonymity to protect his privacy, is one of the few reported cases of people infected after a partial or even full vaccination. Nearly 83 million Americans have received at least one dose of a Covid vaccine and it is unclear how many of them will have a “breakthrough” infection, although two new reports suggest the number is very low.

One study found that only four of 8,121 fully vaccinated employees at Southwestern Medical Center in Dallas became infected. The other found that only seven of 14,990 workers at UC San Diego Health and the David Geffen School of Medicine at the University of California at Los Angeles two or more weeks after receiving a second dose of the Pfizer BioNTech or Moderna vaccines tested positive. Both reports, published Tuesday in the New England Journal of Medicine, show how well the vaccines work in the real world and during a period of intense transmission.

While these breakthrough cases are quite rare, they are a clear reminder that vaccinated people are not invincible, especially if the virus remains widespread.

“We strongly believed that this data shouldn’t lead people to say, ‘Let’s all vaccinate and then we can all stop wearing masks,” said Dr. Francesca J. Torriani, an infectious disease specialist at UC San Diego Health, which led the California study, “These measures must continue until a larger part of the population is vaccinated.”

Only some of the Covid-positive health workers in the California study showed symptoms, she said, and they tended to be mild, suggesting the vaccines were protective. This reflects data from the vaccine trials, which suggest that breakthrough infections were mild and did not require hospital admissions. Some people had no symptoms at all and were only discovered through tests in studies or as part of their medical care.

Updated

March 23, 2021, 11:41 a.m. ET

For example, doctors at the University of North Carolina found some asymptomatic cases in vaccinated patients tested for coronavirus before surgery or other medical procedures, according to Dr. David Wohl, the medical director of this center’s vaccination clinic.

He said the lack of symptoms may have caused the vaccine to do exactly what it was supposed to do: stop people from getting sick, even if it doesn’t completely stop the virus from infecting them.

The Centers for Disease Control and Prevention has a small team studying breakthrough cases, said an agency spokeswoman Kristen Nordlund. One question the researchers are asking is whether certain variants of the coronavirus could play a role in breakthrough cases.

“There is currently no evidence that Covid-19 occurs after vaccination due to changes in the virus,” said Ms. Nordlund.

In the next few months, Pfizer and Moderna are expected to release data showing how often people who have been vaccinated become infected with the virus, even if they don’t show symptoms. The companies tested participants in their vaccine trials for antibodies to a protein called N, which is part of the coronavirus but not part of the vaccine. Finding these antibodies means that a vaccinated person has been infected with the virus. Some study volunteers also have their noses wiped regularly to test for an active viral infection.

Another question is how effective are the vaccines in people whose immune systems have been weakened by illness or medication, said Dr. William Schaffner, an infectious disease expert at Vanderbilt University. Breakthrough cases can occur in these people because their bodies cannot produce a robust response to a vaccine.

“And it’s amazing how widespread immunodeficiency is,” said Dr. Conductor. He called the disease “a testament to modern medicine” because many patients with the disease are successfully treated for conditions that would have killed them not so long ago.

The doctor, who fell ill in New York despite being fully vaccinated, stayed home in isolation for almost two weeks. He described his illness as relatively mild and said he had been treated with monoclonal antibodies to fight the virus. “If the worst flu is a 10, it was a four,” he said.

Without the vaccine, he said, he thinks he would have been sicker.

“I would have been afraid for my mortality,” he said. “But I wasn’t afraid for a moment. I didn’t think I was going to die. I think you won’t die – that’s a pretty big deal. “

Apoorva Mandavilli contributed to the coverage.

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