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BOSTON -- A yearly booster with an mRNA-based COVID vaccine may provide the best protection against catching the pandemic disease, a new analysis of the phase III COVE trial suggested.

"Interestingly, we found that the longer duration between boosting actually provides better protection against COVID-19," Dean Follmann, PhD, of the National Institute of Allergy and Infectious Diseases in Bethesda, Maryland, said here at the . There was a 24% reduced risk of catching Omicron if the time between the original vaccination and booster was 12.9 months compared with 8.2 months, he reported.

Follmann explained that in the -- the study that led to emergency use authorization of Moderna's mRNA vaccine -- it became apparent that the effectiveness of the vaccine waned after a period of months, and the trial protocol was amended to allow for boosters. However, because the amendment occurred during the trial, participants were given boosters at different times. This gave researchers a chance to employ statistical methods to calculate when the best times for giving boosters would be.

"We knew that the original two-dose regimen of mRNA-1273 was highly efficacious and resulted in an emergency use authorization in December of 2020," Follmann said. "Later data through the blinded phase of that trial showed that this durability worked for months, but since then, we've learned that immunity wanes over time, but if it's boosted or increased with a third dose of mRNA-1273 it shows increases in both binding and neutralization assays. We also know that adults older than 50 are at increased risk of severe COVID-19 outcomes."

He noted that among people age 65 and older, there was an initial vaccine efficacy of 86% against the Omicron strain, which waned to 28% after about 4 months. For people under 65, the initial vaccine efficacy against Omicron was 50%, and that protection waned to around 6% after 4 months, he said.

Annual Booster 'Makes Sense to Me'

Session moderator Rajesh Gandhi, MD, of Massachusetts General Hospital/Harvard Medical School in Boston, called the data "important," and told MedPage Today: "What I am telling colleagues and patients is that an annual COVID-19 vaccine makes sense to me. I will be getting my annual vaccine in the next few weeks."

"People who have not had a vaccine for a year or more would be well served in getting one, particularly if they are at high risk for severe disease," Gandhi continued. "We have seen over and over again during the SARS CoV-2 Omicron era that there is benefit from the vaccine, but it is not an indefinite benefit. I think it shows that you can't rely on a vaccine from a year ago, or especially 2 years ago, to be fully protective today. We probably should be getting an annual COVID-19 vaccine going forward."

Study Details

The analysis assessed protection coverage of the original monovalent mRNA-1273 vaccine, Follmann said. Boosting efficacy was evaluated against Delta and BA.1 Omicron, the strains circulating during the boosting period in the study (September 2021 to April 2022).

For the current analysis, Follmann and colleagues evaluated the effectiveness of the mRNA-1273 50 μg booster -- the so-called third dose of the Moderna vaccine -- in 17,025 adult participants (48% women, more than 77% white) who previously received two doses of 100 µg mRNA-1273 during the randomized placebo-controlled phase or in the open-label phase in 2020-2021. A total of 8,298 participants (mean age 54.5) were in the early-boosted group and 8,727 participants (mean age of 51.8) were in the late/never-boosted group.

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