FDA not yet sold on Covid-19 booster jabs, as Pfizer & Moderna share data showing their vaccines lose efficacy over time

US regulators at the FDA say it’s too early to throw support behind Covid-19 booster shots, noting that more data is needed before the agency takes a position, even after President Joe Biden set a hard date for a booster campaign.

A Food and Drug Administration (FDA) briefing document published on Wednesday said the agency still hasn’t independently reviewed or verified the underlying data from the relevant studies on Covid-19 boosters, so it’s not prepared to take a position on whether additional doses should be allowed. The regulator noted that an advisory committee will review data from some of the studies, including the booster program in Israel, on Friday, when it considers Pfizer-BioNTech’s request to allow additional doses.

The statement came after Pfizer-BioNTech and Moderna released data that seemed to suggest that because their vaccines lose effectiveness over time, the US government should buy more to administer booster shots. Pfizer and its German partner BioNTech said a third dose of their vaccine given six months after the second jab restores protection from Covid-19 infection back up to 95%.

Moderna made much the same argument on Wednesday, saying so-called “breakthrough” infections in vaccinated people show that booster shots should be authorized. The company said those who were vaccinated during its clinical trials in July-October 2020 were far more likely to catch the virus than those who got their two shots between December 2020 and March 2021 due to waning vaccine-induced immunity.

There were 162 breakthrough infections in the first group in a study done earlier this summer, compared with 88 cases among those who were vaccinated more recently. The rate of infections per person was 57% higher in the early inoculation group.

“The increased risk of breakthrough in this analysis quantifies the impact of waning immunity...,” Moderna said. “The company believes this adds to evidence of potential benefit of a booster dose.”

However, FDA staffers expressed skepticism about the new data, saying “there are known and unknown biases” that can affect the reliability of such observational studies, as opposed to formal clinical trials. The agency also cited mixed results from observational studies on the durability of protection amid spread of Covid-19’s Delta variant.

“Overall, data indicate that currently US-licensed or authorized Covid-19 vaccines still afford protection against severe Covid-19 disease and death in the US,” the FDA said.

Two FDA vaccine researchers resigned last month, reportedly at least in part because the Biden administration announced plans for a booster roll-out, set to begin on September 20, despite not having secured regulatory approval. While the announcement was backed by US health agencies publicly, it reportedly sparked concerns in private among higher-ups, with the heads of both the FDA and CDC voicing reservations to the White House that Biden’s announcement was premature, according to Axios and the New York Times. 

Israel’s Health Ministry is scheduled to brief the FDA advisory committee on its booster-shot data, though its results also are observational. Israel began administering third doses on August 1 and has begun lining up more supplies in case a fourth jab is needed, despite the World Health Organization’s call in August for a moratorium on booster shots in rich nations because of vaccine shortages around the world.

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