A booster dose of Moderna’s COVID-19 vaccine bolsters the body’s immune response to the omicron variant, the company said, encouraging news that comes as the country appears to enter a holiday surge.

Moderna scientists reported Monday that a dose of 50 micrograms, half of a full dose of the vaccine, increased antibody levels against the omicron variant 37-fold in lab tests. A full 100-microgram dose, meanwhile, was even more effective, boosting antibody levels 83-fold compared to pre-boost levels. The increased antibodies were observed in people 29 days after getting boosted.


“The dramatic increase in COVID-19 cases from the Omicron variant is concerning to all. However, these data showing that the currently authorized Moderna COVID-19 booster can boost neutralizing antibody levels 37-fold higher than pre-boost levels are reassuring,” said Moderna CEO Stephane Bancel.

Adverse reactions to the booster shots were similar to those after the first two shots. Some of the most common reactions to the Moderna vaccine include soreness at the injection site, chills, and fatigue. Often, the side effects experienced after receiving a vaccine signal that the immune system is responding and the vaccine is working. People who received the higher, 100-microgram dose were more likely to experience adverse reactions than those who took the half dose.

The company said it will continue working on variant-specific boosters, which include mutations from former variants of concern, such as delta and beta. Moderna is developing an omicron-specific booster and expects to begin testing early next year.

“To respond to this highly transmissible variant, Moderna will continue to rapidly advance an Omicron-specific booster candidate into clinical testing in case it becomes necessary in the future,” Bancel said. “We will also continue to generate and share data across our booster strategies with public health authorities to help them make evidence-based decisions on the best vaccination strategies against SARS-CoV-2.”

Pfizer, another COVID-19 vaccine-maker, announced earlier this month that its booster shots also significantly increased the body's antibody response to thwart the omicron variant. Currently, all adults 18 and older who were fully vaccinated with either Pfizer's or Moderna’s vaccine at least six months ago can get a booster.


The Biden administration has stepped up calls for eligible people to get their booster shots as soon as possible, especially ahead of the holidays, when many will travel to see relatives and gather indoors, increasing the risk of transmission.

“We really do want people to be able to gather and gather safely,” Centers for Disease Control and Prevention Director Rochelle Walensky said last week. “Use the next week to make sure you're practicing those safe prevention mitigation strategies so that when you come together for the holidays, that people have not been exposed to the virus because, in fact, they've been vaccinated, boosted, and masked.”