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Posts misrepresent Pfizer data on vaccine efficacy

August 4, 2021 GMT

CLAIM: Because 14 people in Pfizer’s placebo group died and 15 people in the vaccinated group also died, Pfizer’s data shows its COVID-19 vaccine does not reduce the risk of dying from the disease.

AP’S ASSESSMENT: False. Those figures reflect deaths from all causes during Pfizer’s ongoing study of its vaccine. Pfizer’s data shows that the vaccine is highly effective at preventing serious illness. Data from countries that have used the vaccine widely shows it is also effective at preventing death from COVID-19.

THE FACTS: Last week, Pfizer released updated data from its vaccine study showing that as of mid-March, the shots were 97% effective in preventing severe disease from COVID-19 up to six months later. The data also showed the shots’ efficacy against COVID-19 symptoms dropped slightly with time: it peaked at 96% efficacy 2 months after the shots were administered and fell to 84% after 6 months.

The Food and Drug Administration granted emergency use authorization for the company’s vaccine in December 2020 after reviewing earlier data from Pfizer’s ongoing study, which includes 44,000 participants. The data Pfizer released on July 28 includes six months of follow-up data that is required to get full FDA approval.

It is expected that in any long-term study, some participants will die. Clinical trials have to monitor deaths that occur during the study as a way to watch for any potential red flags.

Pfizer’s study states that fourteen people in the placebo group and 15 people in the vaccinated group died before January 2021. The vast majority of the deaths were unrelated to COVID-19. Only two people in the placebo group died of COVID-19 and one person in the vaccinated group died of COVID-19 pneumonia, according to additional Pfizer data obtained by The Associated Press. The rest of the deaths were due to other factors, including heart disease and heart attacks.

The report states that none of the deaths were related to the vaccine.

A widely shared Twitter post misrepresented the significance of the death numbers to falsely suggest those deaths meant the Pfizer’s vaccine doesn’t reduce a person’s chance of dying from the virus: “The pivotal clinical trial for the @pfizer #Covid vaccine shows it does nothing to reduce the overall risk of death. ZERO. 15 patients who received the vaccine died; 14 who received placebo died,” the tweet reads.

But those death figures, which include everyone in the study who died before January 2021, are irrelevant to the question of how efficient the vaccine is at preventing COVID-19 deaths.

The claim made in the Twitter post “is not supportable by these data,” said Dr. David J. Cennimo, an infectious disease expert at the Rutgers New Jersey Medical School.

The fact that both the vaccinated group and the control group had a similar number of deaths from causes other than COVID-19 is to be expected, Cennimo said.

“To exaggerate the example for learning, the Pfizer vaccine doesn’t protect you from lightning strikes so equal numbers of people in the vaccine and the placebo control group should get hit by lightning,” Cennimo said.

In fact, the tweet’s assertion that the Pfizer study aimed to measure efficacy against death is also wrong, Cennimo said. Rather, the study was designed to look at how effective the vaccine is at protecting against symptomatic illness.

Since death from COVID-19 is a much rarer event than a COVID-19 infection, Cennimo said a much larger study sample is needed to answer that question. Real-world data from hundreds of millions of Pfizer vaccine doses administered in the United States, the United Kingdom and Israel, show that the vaccine is exceedingly effective at protecting against death.

Cennimo said it would be concerning if the study showed a significant increase in deaths from a specific cause in the vaccinated group, as that would signal a possible adverse vaccine effect. Instead, the data showed the vaccinated deaths were distributed among a number of causes between both groups.

A spokesperson for Pfizer told the AP the company could not comment on specific cases, but said, “No deaths were considered by the investigators to be related to the vaccine or placebo.”


This is part of AP’s effort to address widely shared misinformation, including work with outside companies and organizations to add factual context to misleading content that is circulating online. Learn more about fact-checking at AP.