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Moderna says Omicron antibodies from its booster fall sharply from initial peak, but are still present after six months

The study findings, published in New England Journal of Medicine, are in line with earlier Pfizer results.

A health care worker prepares a dose of Moderna's COVID-19 vaccine booster in Taiwan earlier this month.I-Hwa Cheng/Bloomberg

Virus-fighting antibodies that protect against the Omicron variant of COVID-19 persist six months after a booster of Moderna’s coronavirus vaccine, but decline from peak levels soon after the third shot, the Cambridge biotech said Wednesday.

A laboratory study found that the third shot of Moderna’s messenger RNA vaccine caused antibody levels to climb 20-fold within four weeks, according to a study published in the New England Journal of Medicine. Five months later, antibody levels had fallen 6.3-fold, but were still detectable.

The laboratory study used blood samples from people who had received the booster shot and tested the antibodies against the Omicron variant. The research took place at the National Institute of Allergy and Infectious Diseases, the federal agency that helped Moderna develop its vaccine, and at Duke University Medical Center.


Moderna’s chief executive, Stephane Bancel, said company executives were “reassured by the antibody persistence against Omicron at six months” after a shot of the 50-microgram booster. But because of the “long-term threat” posed by falling levels, the biotech had begun to test an Omicron-specific booster shot in a clinical trial.

About 600 volunteers who are 18 and older are expected to participate in the trial, which will be undertaken at as many as 24 sites in the US. Half of the volunteers will have received the two primary doses of the original Moderna vaccine. The other half will have also received the original booster.

Both groups will receive a mRNA booster dose that Moderna has tailored to Omicron. Researchers vaccinated the first volunteer on Wednesday.

The results of the lab study of Moderna’s original booster in the face of Omicron resembled those published last weekend on a preprint server about antibody levels stimulated by a third Pfizer-BioNTech shot against the variant. That study, which had not been peer-reviewed, indicated that antibodies persisted four months after the Pfizer booster although they, too, had declined.


Multiple lab studies have indicated that the Omicron variant causes antibody levels to fall more rapidly than they did against the original SARS-CoV-2 virus. Antibodies fell only 2.3-fold in the six months after people received two Moderna shots when the original virus was circulating.

Antibodies, however, are only one component of the immune response to diseases. Researchers have repeatedly said that people who are fully vaccinated against COVID-19 and have received boosters appear to remain well-protected from severe disease and hospitalization even if antibody protection wanes.

Another arm of the immune system, T cells, or the white blood cells that fight infection, also appears to be stimulated by the vaccines and protect inoculated people even when antibody levels fall.

Jonathan Saltzman can be reached at jonathan.saltzman@globe.com.