I reiterate our call: “slow down and get the science right”
- “…the FDA’s expectation is of “at least 50%” efficacy for any approvable vaccine.”
- “…it is notable that evidence of waning immunity was already visible in the data by the 13 March 2021 data cut-off.”
- “But although this additional information was available to Pfizer in April, it was not published until the end of July.”
- “Until new clinical trials demonstrate that boosters increase efficacy above 50%, without increasing serious adverse events, it is unclear whether the 2-dose series would even meet the FDA’s approval standard at six or nine months.”
- “So despite this preprint appearing a year after the trial began, it provides no data on vaccine efficacy past six months”
- “It is hard to imagine that the <10% of trial participants who remained blinded at six months (which presumably further dwindled after 13 March 2021) could constitute a reliable or valid sample to produce further findings”
- “…no reported data past 13 March 2021, unclear efficacy after six months due to unblinding, evidence of waning protection irrespective of the Delta variant, and limited reporting of safety data”
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.