FDA is cautious ahead of revaccination meeting

Influential government advisers will discuss on Friday whether there is enough evidence that a booster dose of Pfizer’s COVID-19 vaccine is safe and effective – the first step towards deciding which Americans will need it and when.

On Wednesday, the FDA released much of the evidence that its advisory group will consider. The agency chose a strongly neutral tone in justifying boosters, an unusual and cautious approach that was particularly startling after President Joe Biden and his top health advisers announced a booster campaign they hoped to launch next week.

Pfizer’s argument: While protection against severe disease in the US remains strong, immunity against milder infections wanes about six to eight months after the second dose. At the time, the company had given an additional dose to 306 people and recorded levels of antibodies that fight the virus three times higher than previous vaccinations.

More importantly, Pfizer said, these antibodies appear strong enough to deal with the highly infectious delta variant that is spreading across the country.

To back up its argument, Pfizer pointed the FDA to data from Israel, which began offering boosters in the summer.

This study tracked about 1 million people aged 60 and over and found that those who received the additional vaccine were much less likely to become infected soon after. According to Pfizer, this translates into “approximately 95% efficacy” in spreading delta, comparable to the protection seen shortly after the introduction of the vaccine earlier in the year.

Israeli figures, also published Wednesday in the New England Journal of Medicine, cannot say how long the enhanced protection will last.

The FDA reviewers, however, suggested that they would be focusing on studies of how vaccines work among Americans, stating that “may most accurately reflect the vaccine’s effectiveness in the US population.”

Overall, the data shows that Pfizer and other US-sanctioned COVID-19 vaccines “continue to provide protection against severe COVID-19 illness and death in the United States,” the agency said, summarizing the evidence.

The FDA is not required to follow the advice of its independent advisory panel. But if the agency rejects its own experts, it could cause public confusion. Earlier this week, two of the FDA’s top vaccine regulators joined a group of international scientists who have ditched boosters for healthy people, citing strong, ongoing protection against serious illness.

Dr Anna Durbin of the Johns Hopkins School of Public Health said it’s important to understand that the FDA’s decision is simply about whether the extra dose is safe and does what it says it does – boosts immunity.

If the FDA decides that the extra shot does those two things, the Centers for Disease Control and Prevention will have to decide who should get the extra dose. The CDC has scheduled a meeting of its own advisers for next week and made it clear that it is considering increasing the dose for certain people, such as the elderly, nursing home residents, and frontline healthcare professionals, rather than the general population.

The broader question is: “What will really control the delta option is vaccination of unvaccinated people, not boosters,” Durbin said. More than one-third of Americans who can be vaccinated are not yet fully vaccinated, according to the CDC.

The US is already offering an additional dose of Pfizer or Moderna vaccines to people with severely weakened immune systems.

What indicates a weakening of immunity for an ordinary person? The CDC says real-world data show that protection against serious illness, hospitalization, and death remains strong. But in one recent study, protection against infection declined as the delta variant emerged: it was 91% in the spring, but 78% in June and July. The CDC also noticed a hint that for people 75 and older, hospital admissions protection dropped slightly in the summer.

Moderna also asked the FDA to authorize revaccination of its vaccine, and on Wednesday published its own study of weakening the immune system.

Researchers compared about 14,000 people in the 2020 Moderna vaccine study who received their first dose about a year ago, with another 11,000 vaccinated last winter, roughly eight months ago. As the delta rose sharply in July and August, Moderna concluded that the recently vaccinated group had 36% lower rates of breakthrough infections than the older group.

It is unclear how soon the FDA will consider a Moderna booster or a vaccine for people who receive a single dose of Johnson & Johnson’s vaccine.