Scientific advisers to the Centers for Disease Control and Prevention are meeting on Wednesday and Thursday to decide which Americans should get booster shots of the Pfizer-BioNTech coronavirus vaccine — and when.
The committee’s discussions are normally a scientific affair of little interest to most people. But this meeting is likely to be closely watched — the stakes are high. It follows a dramatic exchange at the Food and Drug Administration on Friday, when advisers overwhelmingly rejected a proposal to offer Pfizer booster shots for Americans over 16, but then voted unanimously in favor of third doses for some high-risk people and those older than 65.
The role of the C.D.C. advisers at the two-day meeting is to decide who belongs in those high-risk groups. Depending on their verdict, booster shots could be offered to most Americans — or only to a select few.
On Wednesday, the discussion zeroed in on the types of immunity. Natalie Thornburg, a C.D.C. scientist, presented results from a series of studies suggesting that declining levels of antibodies may have little impact on protection from severe illness. Some subsets of antibodies are needed to prevent infection, but immune cells that prevent the illness from progressing are stable, she said.
“Antibodies decrease over time as we expected, in all age groups, but cellular memory is maintained,” she said. Immunity is known to drop off in adults over 80, however, suggesting that boosters may be needed for that age group.
Dr. Sarah Long, a pediatric infectious disease expert at Drexel University College of Medicine in Philadelphia, urged fellow committee members to focus on how well the vaccines prevent severe illness and hospitalization.
“I would just encourage us not to lump infection and hospitalization,” she said. “I don’t think there’s any hope that vaccines such as the ones we have will prevent infection, after the first maybe couple weeks that you have those extraordinary immediate responses.”
If the F.D.A. authorizes the Pfizer-BioNTech booster dose for some high-risk groups and older adults, advisers to the C.D.C will vote on Thursday to make their recommendations. But it is likely to be too late for the Biden administration, which had planned to begin offering third doses this week to most fully vaccinated adults in the United States.
At the meeting on Friday, senior scientists at Pfizer and the Israeli Ministry of Health presented data they said indicated waning immunity in people who received the Pfizer vaccine months earlier. Boosting immune defenses with a third shot has made a difference in Israel, they said, and could stem the tide of infections in the United States.
The F.D.A. advisers also evaluated data from the C.D.C. on the trajectory of the virus in the United States, as well as summaries from several studies on the effectiveness of the vaccines.
But after reviewing the evidence, the scientists on the committee concluded that while protection against infection may be waning, especially in older adults, the original two-shot regimen still offers excellent protection against severe illness and hospitalization in most people.
“It’s unclear that everyone needs to be boosted, other than a subset of the population that clearly would be at high risk for serious disease,” said Dr. Michael G. Kurilla, a committee member and official at the National Institutes of Health.
One key difference between Israel and the United States may explain why the two countries have had different experiences with the vaccine: The countries define severe illness differently.
Understand Vaccine and Mask Mandates in the U.S.
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- Vaccine rules. On Aug. 23, the Food and Drug Administration granted full approval to Pfizer-BioNTech’s coronavirus vaccine for people 16 and up, paving the way for an increase in mandates in both the public and private sectors. Private companies have been increasingly mandating vaccines for employees. Such mandates are legally allowed and have been upheld in court challenges.
- Mask rules. The Centers for Disease Control and Prevention in July recommended that all Americans, regardless of vaccination status, wear masks in indoor public places within areas experiencing outbreaks, a reversal of the guidance it offered in May. See where the C.D.C. guidance would apply, and where states have instituted their own mask policies. The battle over masks has become contentious in some states, with some local leaders defying state bans.
- College and universities. More than 400 colleges and universities are requiring students to be vaccinated against Covid-19. Almost all are in states that voted for President Biden.
- Schools. Both California and New York City have introduced vaccine mandates for education staff. A survey released in August found that many American parents of school-age children are opposed to mandated vaccines for students, but were more supportive of mask mandates for students, teachers and staff members who do not have their shots.
- Hospitals and medical centers. Many hospitals and major health systems are requiring employees to get a Covid-19 vaccine, citing rising caseloads fueled by the Delta variant and stubbornly low vaccination rates in their communities, even within their work force.
- New York City. Proof of vaccination is required of workers and customers for indoor dining, gyms, performances and other indoor situations, although enforcement does not begin until Sept. 13. Teachers and other education workers in the city’s vast school system will need to have at least one vaccine dose by Sept. 27, without the option of weekly testing. City hospital workers must also get a vaccine or be subjected to weekly testing. Similar rules are in place for New York State employees.
- At the federal level. The Pentagon announced that it would seek to make coronavirus vaccinations mandatory for the country’s 1.3 million active-duty troops “no later” than the middle of September. President Biden announced that all civilian federal employees would have to be vaccinated against the coronavirus or submit to regular testing, social distancing, mask requirements and restrictions on most travel.
In Israel, anyone with an accelerated respiratory rate and an oxygen level of below 94 percent is severely ill. By contrast, the C.D.C. reserves that category for people who are sick enough to be hospitalized, said Dr. Sara Oliver, a C.D.C. scientist who presented the American data.
Some committee experts said they also did not feel comfortable offering booster shots to young people who may not need them, when the risks of a third dose are unknown.
The vaccines have been tied to rare cases of myocarditis, inflammation of the heart, in younger people. The risk is very small, and studies have shown that Covid-19 is much more likely to cause the condition.
Last week brought other research in support of the F.D.A. committee’s decision, including one paper by an international team of scientists that analyzed dozens of studies and concluded that the world would be better served by using vaccine doses to protect the billions who remain unvaccinated.
The authors of that study included the top two vaccine experts at the F.D.A., who announced plans to leave the agency this fall. Their departure is in part in protest of the Biden administration’s push for boosters before federal scientists and regulators had reviewed the evidence.