Study links Pfizer COVID-19 vaccine to higher death rates than Moderna shot

A new peer-reviewed study involving nearly two million adults in Florida has reported higher mortality rates among recipients of Pfizer’s original mRNA COVID-19 vaccine compared with those who received Moderna’s vaccine.

The study, published in the journal Global Epidemiology, found statistically significant associations between Pfizer vaccination and higher rates of all-cause mortality, cardiovascular deaths and COVID-19-related deaths during the year following vaccination.

However, the researchers cautioned that the findings do not establish that Pfizer’s vaccine caused the additional deaths.

The study analysed vaccination and death records involving 1,962,822 Florida adults who received their first Pfizer or Moderna COVID-19 vaccine dose between December 2020 and August 2021.

To improve the reliability of the comparison, researchers matched nearly one million Pfizer recipients with an equal number of Moderna recipients based on factors including age, sex and vaccination dates.

The analysis recorded 784 deaths from all causes among Pfizer recipients, compared with 562 among those who received Moderna.

According to the researchers, the difference represented approximately 221 additional deaths per 100,000 people in the Pfizer group during the study period.

The mortality differences were particularly pronounced among adults aged 60 and above, although higher overall death rates were reported among Pfizer recipients across the age groups examined.

Florida Surgeon General Joseph Ladapo and Retsef Levi, a professor of operations management at the MIT Sloan School of Management and member of the now-suspended Advisory Committee on Immunization Practices (ACIP), were among the study’s co-authors.

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Reacting to the findings, Ladapo described the research as an example of the type of investigation that public health departments should undertake to examine vaccine safety.

He argued that the findings highlighted weaknesses in the existing system for evaluating vaccine safety and called for reforms.

In a post on X, Ladapo said the findings supported his decision to stop recommending mRNA COVID-19 vaccines, arguing that the results raised serious concerns about their safety.

He also suggested that the difference in mortality rates, if extrapolated nationally and globally, could represent a substantial number of deaths.

However, Ladapo cautioned against interpreting the findings as proof that Moderna’s vaccine is safe.

He cited previous research, including a 2022 study published in Vaccine, which raised concerns about serious adverse events following Moderna vaccination.

Levi also emphasised that the study was not designed to establish causation but added that it contributed to growing evidence suggesting that Pfizer and Moderna vaccines could have different effects beyond their intended protection against COVID-19.

The researchers identified several possible explanations for the mortality differences.

One possibility is that Moderna’s vaccine provided stronger protection against COVID-19 infection and its complications.

Another is that differences in the vaccines’ formulations could have produced different biological effects.

The two vaccines differ in their ingredients, mRNA doses, manufacturing processes and delivery systems. However, the researchers said the precise biological reasons behind the observed mortality differences remain unknown.

To strengthen their analysis, the researchers examined deaths resulting from cancer, suicide and homicide, which they considered unlikely to be influenced by the type of vaccine received.

They found no statistically significant differences in these outcomes between the two groups.

The findings also showed similarities with two earlier studies involving recipients of Pfizer and Moderna vaccines in the United States.

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A nationwide study published in 2022, involving 433,672 veterans, reported higher risks of stroke, myocarditis, blood clots and kidney injury among Pfizer recipients compared with Moderna recipients.

Another study involving 902,235 people within the US Veterans Affairs healthcare system found higher risks of COVID-19 infection and hospitalisation among Pfizer recipients, with the differences becoming more pronounced with increasing age.

Ladapo said the Florida study expanded on previous research through its larger sample size, matching procedures and analytical methods.

Despite the findings, some researchers have raised concerns about possible limitations in the study.

Karl Jablonowski, senior research scientist at Children’s Health Defense, noted that Pfizer’s vaccine became available before Moderna’s, potentially influencing which categories of people received each vaccine first.

According to him, the early availability of Pfizer’s vaccine may have resulted in more vulnerable individuals receiving it, creating a possible confounding factor in the mortality comparison.

He also pointed to a supplementary analysis showing an inverse relationship among adults aged 18 to 59, in which Moderna vaccination was associated with a higher all-cause mortality hazard.

Jablonowski said this discrepancy deserved further examination.

Levi, however, maintained that the researchers’ negative-control analysis did not show evidence of significant unobserved confounding.

The researchers also acknowledged that their observational study had limitations, including the absence of detailed medical records that could have provided information about participants’ underlying health conditions.

They further noted that some causes of death might have been incorrectly classified because of errors in death certificates.

Another limitation was the absence of an unvaccinated comparison group, meaning the study could not establish how mortality among Pfizer and Moderna recipients compared with people who received neither vaccine.

Despite these limitations, the researchers argued that the large sample size, extensive matching process and consistency with previous studies supported the relevance of their findings.

They stressed that COVID-19-related and non-COVID-19 health outcomes should both be considered when assessing vaccine safety.

The findings are expected to add to ongoing scientific discussions about differences between COVID-19 vaccines, their long-term safety profiles and the need for stronger post-vaccination monitoring.