FDA scientists skeptical of COVID-19 booster evidence ahead of key meeting

Food and Drug Administration (FDA) scientists on Wednesday did not immediately endorse the evidence that a booster dose of the Pfizer-BioNTech COVID-19 vaccine was necessary for all Americans who received the shot.

In documents posted online ahead of a key FDA vaccine advisory committee meeting Friday, agency staff sounded skeptical of the evidence presented by the drug company and noted that all available data has not been submitted or reviewed yet.

“Overall, data indicate that currently US-licensed or authorized COVID-19 vaccines still afford protection against severe COVID-19 disease and death in the United States,” scientists said in a briefing document. 

The FDA’s independent panel of experts on Friday will review the evidence from Pfizer and will likely vote on whether there’s enough evidence to show boosters are necessary.

The FDA does not have to follow the agency’s advice, but if the agency breaks with the panel’s recommendation it would likely stoke public confusion and raise major questions about political interference.

If the FDA panel recommends a booster dose, the agency will formally accept the decision, and then a separate advisory committee convened by the Centers for Disease Control and Prevention (CDC) will vote on whether to administer them broadly.

In an unusual move last month, President Biden and top health officials publicly announced a booster shot program would begin the week of Sept. 20, well before the FDA and CDC examined the evidence.

While officials have been careful to say the booster program is contingent on the FDA and CDC giving the green light, they have been criticized by some public health experts for speaking as if the approval was a given.

In making its case for a third dose, Pfizer argued that protection against COVID-19 infection wanes primarily because of time, rather than because of the delta variant.

Pfizer cited evidence from lab studies as well as real-world data from Israel, which has been administering boosters to people over 60 since the end of July. The country recently expanded boosters to people over age 30.

“The totality of the available data supports the public heath need for a booster [third] dose … at approximately 6 months after the second dose” for individuals 16 years of age and older, Pfizer wrote.

Pfizer is seeking FDA licensure for boosters in Americans over the age of 16. The FDA said the company met predefined criteria for success.

The third vaccine dose was “well-tolerated” among study participants, Pfizer said, with no serious adverse events or deaths reported. Mild to moderate injection site pain, fatigue, chills and muscle soreness were commonly reported side effects.

Citing the Israeli data, Pfizer said that a third dose restores protection from infection to 95 percent in a real-world setting, the same level of protection at the end of the initial dosing regimen. The data was collected from July 1 through Aug. 30, a period when the delta variant was spreading.

But the FDA staff said the evidence presented to the agency is mixed and they could rely on data from the U.S., rather than Israel.

“There are many potentially relevant studies, but FDA has not independently reviewed or verified the underlying data or their conclusions,” the staff report said.

The FDA said some of those studies, including the Israeli data, will be discussed Friday.

Still, FDA reviewers wrote U.S.-based studies of post-authorization effectiveness “may most accurately represent vaccine effectiveness in the US population.”

The Biden administration has cited Israeli data showing waning immunity as the primary reason for pushing boosters, despite disagreement among experts and some agency staff.

Among those who have challenged the need for a booster dose are two senior FDA scientists in the office that reviews vaccines. Marion Gruber and Philip Krause recently decided to retire this fall, seemingly over disagreement about boosters.

The U.S. already offers a third dose of the Pfizer or Moderna vaccines to people with severely weakened immune systems, though there is no requirement for people to show proof.