This, he thought, could not be happening. But it was: He tested positive for the coronavirus.
“It was a huge shock,” he said. He knew that no vaccine was perfect and that the Pfizer-BioNTech shots he received had been found 95 percent effective in a large clinical trial. “But somehow in my mind, it was 100 percent,” he said.
The doctor, who requested anonymity to protect his privacy, is among the few reported cases of people who have been infected after being partly or even fully vaccinated. Nearly 83 million Americans have received at least one dose of a Covid vaccine, and it’s unclear just how many of them will have a “breakthrough” infection, though two new reports suggest the number is very small.
One study found that just four out of 8,121 fully vaccinated employees at the University of Texas Southwestern Medical Center in Dallas became infected. The other found that only seven out of 14,990 workers at UC San Diego Health and the David Geffen School of Medicine at the University of California, Los Angeles tested positive two or more weeks after receiving a second dose of either the Pfizer-BioNTech or Moderna vaccines.
Only some of the virus-positive health workers in the California study showed symptoms and they tended to be mild, suggesting that the vaccines were protective.
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 considering is whether particular variants of the coronavirus might play a role in breakthrough cases.
“Currently, there is no evidence that Covid-19 after vaccination is occurring because of changes in the virus,” Ms. Nordlund said.
Another question is how effective the vaccines are in people whose immune systems have been weakened by illness or medications, said Dr. William Schaffner, an infectious disease expert at Vanderbilt University. Breakthrough cases might occur in those people because their bodies cannot produce a robust reaction to a vaccine.
“And it is amazing how pervasive immunocompromise is,” Dr. Schaffner said. He called the condition “a testament to modern medicine,” because many patients with it are being treated successfully for conditions that not so long ago would have killed them.
The doctor who became ill in New York despite full vaccination stayed in isolation at home for nearly two weeks. He described his illness as relatively mild, and said he was treated with monoclonal antibodies to fight the virus. “If the worst flu is a 10, this was a four,” he said.
Without the vaccine, he said, he believes he would have been sicker.
“I would have been in fear for my mortality,” he said. “But I didn’t have a moment’s anxiety. I did not think I was going to die. Thinking you’re not going to die — that’s a pretty big thing.”