Does the FDA think these data justify the first full approval of a covid-19 vaccine?
August 23, 2021
The FDA should demand adequate, controlled studies with long term follow up, and make data publicly available, before granting full approval to covid-19 vaccines, says Peter Doshi On 28 July 2021, Pfizer and BioNTech posted updated results for their ongoing phase 3 covid-19 vaccine trial. The preprint came almost a year to the day after the historical trial commenced, and nearly four months since the companies announced vaccine efficacy estimates “up to six months.”
But you won’t find 10 month follow-up data here. While the preprint is new, the results it contains aren’t particularly up to date. In fact, the paper is based on the same data cut-off date (13 March 2021) as the 1 April press release, and its topline efficacy result is identical: 91.3% (95% CI 89.0 to 93.2) vaccine efficacy against symptomatic covid-19 through “up to six months of follow-up.”
The 20 page preprint matters because it represents the most detailed public account of the pivotal trial data Pfizer submitted in pursuit of the world’s first “full approval” of a coronavirus vaccine from the Food and Drug Administration. It deserves careful scrutiny.
The elephant named “waning immunity”
Since late last year, we’ve heard that Pfizer and Moderna’s vaccines are “95% effective” with even greater efficacy against severe disease (“100% effective,” Moderna said).
Whatever one thinks about the “95% effective” claims (my thoughts are here), even the most enthusiastic commentators have acknowledged that measuring vaccine efficacy two months after dosing says little about just how long vaccine-induced immunity will last. “We’re going to be looking very intently at the durability of protection,” Pfizer senior vice president William Gruber, an author on the recent preprint, told the FDA’s advisory committee last December.
The concern, of course, was decreased efficacy over time. “Waning immunity” is a known problem for influenza vaccines, with some studies showing near zero effectiveness after just three months, meaning a vaccine taken early may ultimately provide no protection by the time “flu season” arrives some months later. If vaccine efficacy wanes over time, the crucial question becomes what level of effectiveness will the vaccine provide when a person is actually exposed to the virus? Unlike covid vaccines, influenza vaccine performance has always been judged over a full season, not a couple months.
And so the recent reports from Israel’s Ministry of Health caught my eye. In early July, they reported that efficacy against infection and symptomatic disease “fell to 64%.” By late July it had fallen to 39% where Delta is the dominant strain. This is very low. For context, the FDA’s expectation is of “at least 50%” efficacy for any approvable vaccine.
Now Israel, which almost exclusively used Pfizer vaccine, has begun administering a third “booster” dose to all adults over 40. And starting 20 September 2021, the US plans to follow suit for all “fully vaccinated” adults eight months past their second dose.
Delta may not be responsible.