Did Florida statistics show that the Pfizer COVID vaccine "likely KILLED over 470,000 Americans" and "increased your risk of death by at least 36%"? No, that's not true: A draft research paper found only that those who got the Pfizer vaccine had a higher rate of death from all causes than did those who received the Moderna vaccine. The research paper did not conclude that Pfizer's COVID-19 vaccine caused more deaths than it prevented.
The claim originated in an April 30, 2025, item (archived here) on Steve Kirsch's Substack blog under the title "New Florida brand differential study shows the Pfizer vaccine likely KILLED over 470,000 Americans" and copies of the claim appeared in posts like this (archived here) and in a meme (archived here). It opened:
This stunning brand comparison study shows the Pfizer shots increased your risk of death by at least 36%. Vaccines are NEVER supposed to INCREASE your risk of death.
This is what the newsletter item looked like on Substack at the time this fact check was written:
(Source: Kirschsubstack.com screenshot taken by Lead Stories.)
Research paper only compared the two vaccines
The lead author of the draft research paper is Florida Surgeon General Joseph Ladapo. Ladapo's co-authors include two of his employees at the Florida Department of Health and Retsef Levi, a professor of operations management at the MIT business school. The draft paper aimed to compare outcomes among Florida patients who took either Pfizer or Moderna COVID vaccines during the early months of the pandemic. Here is the study design, as summarized by the authors:
Objective: To examine the relative impact of the initial series of the messenger RNA (mRNA) BNT162b2 (Pfizer) and mRNA-1273 (Moderna) on all-cause and non-COVID-19 mortality among Florida residents.
It is a so-called "preprint" paper, not yet reviewed by experts in the field, but shared in order to generate discussion and review. The server that hosted the paper, MedRxiv, allows writers to post draft papers but warns readers (archived here) not to use any preprint for making clinical decisions:
... We also urge journalists and other individuals who report on medical research to the general public to consider this when discussing work that appears on medRxiv preprints and emphasize it has yet to be evaluated by the medical community and the information presented may be erroneous.
The authors of the preprint paper analyzed the death certificate data of about 1.4 million of the 9 million Floridians vaccinated in the first nine months after vaccines were approved. Ladapo and Levi found a difference in the number of deaths from all causes of those who received the Pfizer vaccine, on one hand, and those who received the Moderna vaccine, on the other. Those who got the Pfizer shot also had a higher death rate, according to the paper.
The paper did not state that vaccination increased the risk of death from all causes, and it did not calculate the risk of death of those who were not vaccinated during the same period of time. The paper only noted "potential concerning adverse effects on all-cause and cardiovascular mortality" (archived here).
Expert says Kirsch's blog post ignores absence of unvaccinated control group
Lead Stories sent the paper and blog post to vaccinologist Helen Petousis-Harris at the New Zealand-based Global Vaccine Data Network, who provided the following assessment in a May 8, 2025 email to Lead Stories: "It (the Florida data) compares Pfizer to Moderna, not to no vaccine. That's "Epidemiology 101."
And, she wrote, the "increases your risk of death" claim ignores evidence from the real world:
If Pfizer were deadly, countries with high Pfizer coverage (like Israel and New Zealand) would have shown surging excess deaths, but they didn't. NZ had negative excess mortality ... In reality, countries with high Pfizer uptake had lower death rates, and vaccinated people of all brands consistently have better survival than the unvaccinated. That's the real data.
Kirsch made another math error, she said, in his attempt to prove an increased risk from taking the Pfizer vaccine:
Kirsch calculates excess deaths by assuming Moderna has zero risk and Pfizer has all the risk. This is an absurd assumption without evidence. No vaccine is risk-free -- the only fair comparison is vaccinated vs. unvaccinated, not brand vs. brand in isolation.
That error is compounded when Kirsch uses it to claim the Pfizer vaccine killed hundreds of thousands of Americans, she wrote:
He extrapolates a relative difference in death rates in Florida to all of America using crude population-level multipliers. This is mathematical malpractice: you can't project relative risk without adjusting for age, health status, or real-world vaccine uptake patterns across demographics.
The vaccines had the opposite effect to what Kirsch claims, she wrote:
Large-scale studies around the world have repeatedly shown that vaccinated people have lower death rates than unvaccinated individuals, even after adjusting for health status and age. Suggesting that the Pfizer vaccine increases overall mortality, while ignoring the broader evidence that vaccination saves lives, is not just misleading -- it completely disregards the overwhelming body of real-world data.
Petousis-Harris offered as examples a pair of studies published by The Lancet and the New England Journal of Medicine, which found Moderna was slightly more effective than Pfizer.
For other Lead Stories fact checks about Kirsch's claims, start here.
