Study: Boosters Protect Against Severe COVID For About 4 Months

Even if you are fully vaccinated against COVID-19, getting a booster shot is still recommended because it will help protect you against severe illness and poor outcomes if you do get sick.

A large study published in the BMJ that involved over 893,000 adults recently found that the monovalent, or original, mRNA boosters protect against moderate and severe COVID for about four to five months before it starts to wane.

“This study resoundingly reinforces what we have seen in every other study in terms of the short- and longer-term health benefits and overall safety of staying up to date with COVID vaccination,” Mark Loafman, MD, MPH, a family physician and chair of the Family and Community Medicine Department at Cook County Health, told Verywell.

The study’s findings present strong evidence about the effectiveness of booster shots and the need to administer additional boosters to maintain a high level of immunity against COVID.

What Boosters Can and Cannot Do

Loafman said that the study expanded on the original vaccine research trials and provided more details on the effectiveness of the third and fourth COVID vaccine shots in various subgroups.

For example, the study showed that the effectiveness of the Pfizer or Moderna boosters both waned in adults, regardless of how old they were. Vaccine effectiveness also tended to be lower for people who were immunocompromised, and its waning was more evident.

Interestingly, booster vaccines appeared to be particularly good at preventing severe outcomes. The study reported that the protection against moderate disease waned more than that against severe disease.

“First, it’s a very large study which means it has a lot of statistical power to base conclusions on,” Andy Pekosz, PhD, a virologist and the vice-chair of the Department of Molecular Microbiology and Immunology at the Johns Hopkins Bloomberg School of Public Health, told Verywell. “Second, while vaccine efficacy against hospitalization waned, it was still at a pretty good level.”

However, much like the primary vaccine doses, booster shots cannot completely prevent people from getting infected with COVID.

“Omicron, in particular, evaded a good portion of vaccine-induced immunity, which makes the vaccine efficacy numbers get lower faster,” said Pekosz. “If a variant more closely related to the vaccine had been circulating at the time of the study, I expect we could have seen a higher vaccine efficacy.”

How Effective Are Bivalent Boosters?

The study authors analyzed data from January 2021 to July 2022, which covered the periods when the Delta and Omicron variants of the COVID virus were dominant.

Pekosz said that the current bivalent boosters are a better match to the currently circulating variants, so “the protection should be stronger than what is seen in this study.”

A recent study published in the New England Journal of Medicine reported that a bivalent vaccine with the Omicron BA.1 spike protein provided protection against COVID for at least a month. The shot also prompted a higher antibody response against earlier COVID variants, including Alpha, Beta, Gamma, and Delta.

It’s important to keep in mind that these results are from clinical research that’s ongoing, and more data will come out over the long term. That said, the authors of the current study do believe that the findings show the benefit of bivalent boosters.

It’s likely that the protection from bivalent boosters may last as long as the monovalent boosters, but Loafman said that “we need a few more months of large-scale observation following bivalent booster administration to know for sure.”

For now, take note of whether you’re up to date with your COVID boosters. If it’s been at least two months since your last COVID vaccine dose, it’s recommended that you get the updated bivalent booster to have better protection against the Omicron variants BA.4 and BA.5.

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.