Pfizer, Moderna boosters both effective against severe COVID-19 outcomes

January 12, 2023 – Third doses of both the Moderna and Pfizer COVID-19 mRNA vaccines were found to be effective in protecting against SARS-CoV-2 infection and severe COVID-19 outcomes, according to a large study from Harvard T.H. Chan School of Public Health’s CAUSALab and the Veterans Affairs (VA) Boston Healthcare System (VA-CAUSAL collaboration).

The study was published January 2 in the journal Nature Microbiology.

The study looked at two matched groups of 65,196 veterans—one that received the Pfizer vaccine and one that received the Moderna vaccine between October 20, 2021, and February 8, 2022, during which the Delta and Omicron variants of the coronavirus were circulating. Researchers evaluated a range of outcomes, including documented infection, symptomatic COVID-19, hospitalizations, ICU admissions, and deaths. The difference in estimated risk of COVID-19 death over 16 weeks between the two groups was only two-thousandths of one percent.

Researchers got similar results in a further analysis of two matched groups of 7,894 veterans who received third doses of either the Pfizer or Moderna vaccines during a nine-week period when the Omicron variant was predominant.

Given the extremely small differences found in the study, “Individuals interested in getting boosted should be confident in seeking whichever of the two vaccines is first available,” said Barbra Dickerman, assistant professor of global cancer prevention, who was co-first author along with Hanna Gerlovin of the Massachusetts Veterans Epidemiology Research and Information Center, VA Boston.

People receiving the Moderna vaccine had slightly lower risks of the studied COVID-19 outcomes, Dickerman noted. “While small for any individual, these differences may help inform larger decision-making bodies when considering population-level vaccination efforts,” she said.

Other Harvard Chan School co-authors of the study included Arin Madenci and Miguel Hernán.

Read a VA Boston press release: Comparative effectiveness of third-dose mRNA COVID vaccines