Here’s Why Experts Believe the New Omicron Booster Will Work

A study published Sept. 16 in the New England Journal of Medicine (NEJM) makes a strong case for an Omicron-based COVID-19 booster shot.

But first, a caveat: There are no data available yet demonstrating the effectiveness of the new Omicron booster authorized on Aug. 31, which protects against BA.4 and BA.5. The new study, conducted by Moderna, involves the company’s first combined vaccine that never came to market; it targets both the original SARS-CoV-2 virus and an earlier version of the Omicron variant, BA.1. It’s data that the U.S. Food and Drug Administration (FDA) and U.S. Centers for Disease Control and Prevention (CDC) relied on heavily in deciding whether to authorize the combination booster that targets the original virus and the latest Omicron variants, BA.4 and BA.5. Human studies involving the new authorized boosters from Moderna and Pfizer-BioNTech have just begun and won’t be completed for another few months.

The data provided by Moderna in the NEJM study are the best proxy we have right now for how well the new boosters work, and the results are promising. In the study, more than 800 volunteers received either a booster dose of Moderna’s original shot against SARS-CoV-2 or a booster dose of the bivalent booster against both the original and Omicron BA.1 strains. All people in the study had been vaccinated with the primary series of two Moderna doses and boosted once before beginning the study.

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About a month after their shot, people who received the bivalent booster showed higher levels of virus-fighting antibodies than people who got the original booster. The antibodies generated were also able to better bind to and neutralize not just the original and BA.1 viruses, but nearly all of the other known variants as well, including Alpha, Beta, Gamma, Delta, and Omicron BA.4 and BA.5.

Pfizer-BioNTech—which also made a bivalent BA.1 vaccine that didn’t come to market—reported similarly encouraging results of its bivalent BA.1 booster to the FDA’s vaccine expert committee last June, but has not yet published those results in a scientific journal. At the FDA meeting (at which Moderna had also presented its BA.1 bivalent data), Pfizer-BioNTech showed data from a study involving more than 300 people ages 55 and older who received the bivalent booster. People who got it generated significantly higher levels of antibodies against BA.1, as well as BA.4 and BA.5, compared to those receiving the original booster. The level of antibodies was lower against BA.4 and BA.5, however, than the level produced against BA.1. The study also showed that the side effects associated with the Omicron BA.1 bivalent vaccine were similar to those of the original vaccine.

As more people roll up their sleeves to get the new Omicron booster, data on how well the vaccine protects people not just from serious illness, but also from infection, will become clear. Researchers will also be looking at how long that protection lasts. The hope is that better matching the vaccine booster to the circulating strain will afford people more durable protection and lead to yearly, rather than more frequent, shots.