But some researchers and public health officials have cautioned that much of this data is preliminary and people should not assume boosters are necessary. Two shots of the Pfizer or Moderna offer robust and lasting protection against severe disease and death. Johnson & Johnson said the company’s data shows the vaccine was 85 percent effective against severe illness from the Delta variant and protected those who received it against hospitalization and death.
Dr. Krutika Kuppalli, an infectious-disease specialist and an assistant professor of medicine at the Medical University of South Carolina, said many of her patients who got the Johnson & Johnson vaccine have asked if they should get an additional shot. That vaccine, like AstraZeneca’s, is less effective than the mRNA vaccines.
It is not unreasonable for those patients to consider it, she tells them.
But Dr. Kuppalli said she explains to her patients that the data remains murky about potential side effects and the research is not definitive yet. “We actually want science to be driving our policies,” she said.
Terri Givens, a professor at McGill University in Quebec who received the Johnson & Johnson vaccine in March, said she was mulling a booster, but did not want to get ahead of the research.
“I don’t want to do it because it might work,” said Professor Givens, 56, who teaches political science. “I want to do it in a conscientious way where my doctor says it’s OK.”
Given the decentralized system for booking vaccines in the United States, several people said it was easy to get a booster, even though they were not technically allowed.
In its emergency authorizations of the vaccines, the Food and Drug Administration permitted only two doses of the Pfizer and Moderna vaccines and a single dose of the Johnson & Johnson vaccine. Before the C.D.C. could recommend boosters, the F.D.A. would have to change this authorization or fully approve the vaccines. If they were fully approved, then doctors would have more leeway to prescribe a booster for their patients.