In Head-to-Head Comparison, Moderna Bests Pfizer by a Nose

Although the value of comparing the efficacy of two extraordinarily effective vaccines is questionable, a recent study published in the New England Journal of Medicine (NEJM) did exactly that. Researchers from Harvard University and the U.S. Department of Veterans Affairs (VA) found that the Moderna mRNA vaccine was slightly better than the PfizerBioNTech vaccine.

The researchers analyzed electronic health records of veterans across the U.S. Almost all had received two doses of either the Pfizer-BioNTech or Moderna vaccines from January 4 to May 14, 2021.

“Both vaccines are incredibly effective, with only rare breakthrough cases,” said Juan Casas, M.D., Ph.D., an epidemiologist at Brigham and Women’s Hospital in Boston and a Harvard associate professor. “But regardless of the predominant strain—Alpha earlier and then Delta later—Moderna was shown to be slightly more effective.”

The data looked at two groups of 219,842 veterans who received a single dose of either vaccine. In the 24 weeks of follow-up, the estimated risk of COVID-19 was 5.75 events per 1,000 people in people who received the Pfizer-BioNTech vaccine and 4.52 events per 1,000 people with Moderna.

Throughout the study, 2,016 people tested positive for COVID-19, with 559 of them symptomatic. Of all testing positive, 411 (20.4%) were hospitalized, 125 (6.2%) were admitted to an intensive care unit (ICU), and 81 (4.0%) died.

The matched population during the part of the study period where the Delta variant was most dominant was typically younger on average. There was also a more significant percentage of African American participants, current smokers, and those who had not received a flu vaccine in the previous five years. However, there was a lower percentage of people with underlying chronic health conditions.

This is the first study to compare the two mRNA vaccines directly. The differences in their efficacy were negligible and, for an individual getting the vaccines, unlikely to make any difference. When considering vaccinating millions or even billions of people, then from an epidemiological perspective, the numbers might matter.

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First author Barbra A. Dickerman, epidemiology instructor with the Harvard T. H. Chan School of Public Health, noted, “Given the high effectiveness of both the Moderna and Pfizer vaccines, confirmed by our study, either one is recommended to any individual offered a choice between the two. However, while the estimated differences in effectiveness were small on an absolute scale, they may be meaningful when considering the large population scale at which these vaccines are deployed. This information may be helpful for larger decision-making bodies.”

In an accompanying editorial by Eric Rubin, editor-in-chief of NEJM, and Dan Longo, both of Brigham and Women’s Hospital, they said that both vaccines and others will be needed to help vaccinate the developing world.

“Even if they are less able to protect against infection, many of the other available vaccines do a very good job of protecting against severe disease,” they wrote. “Moreover, the study by Dickerman et al. gives us no idea how the vaccines will compare after an additional booster dose. So the lesson we take away is not about differences—it’s about similarities.”

The researchers wrote, “In many countries, the availability of vaccines has marked a turning point in the COVID-19 pandemic. Although the vaccines are imperfect, breakthrough infections in fully vaccinated people remain rare, even with recently emerging variants. Countries with high vaccination rates have largely been able to reopen, and rates of severe illness and death have dropped dramatically.”

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