Moderna said early Monday that a third dose of its COVID-19 vaccine significantly increased immune responses against the Omicron coronavirus variant in lab tests, adding more preliminary evidence that booster shots restore protections eroded by the new variant. 

Moderna said in a press release that the half-dose it has been using as a booster increases neutralizing antibody levels 37-fold that pre-booster levels. Neutralizing antibodies, The Wall Street Journal explains, “are among the first soldiers that the immune system deploys to battle invaders like the coronavirus.” Pfizer reported earlier that its third dose boosted neutralizing antibodies against Omicron more than 25-fold.

“What we showed is when you boost, you get a good brisk increase in antibody levels and they would be correlated with protection,” Moderna Chief Medical Officer Paul Burton told the Journal. Using a full 100-microgram does for the booster pumped up neutralizing antibody levels 83-fold, and Burton said regulators should consider using full doses for people at higher risk of more severe COVID-19. Moderna decided on a half dose for the third shot to reduce adverse effects, usually fevers, fatigue, and muscle aches.  

Dr. Eric Topol, founder and director of the Scripps Research Translational Institute, said a half dose should prove sufficient, if Moderna’s lab research is borne out in the real world. “I think it’s pretty encouraging,” he told USA Today. “We’ll take any positive we can get.”

Omicron has shown itself to evade previous infections and inoculations, though even two doses of the Pfizer and Moderna vaccine (and one dose of the Johnson & Johnson shot plus a Pfizer or Moderna booster) are effective at preventing serious illness and hospitalization. The hope is that a booster shot will also prevent infection and curb the spread of the highly transmissible variant. 

Moderna said it is also testing an Omicron-specific vaccine, but given the time needed to roll out a new vaccine, it is focusing its efforts on producing more of its original formula so people can get boosted.