Moderna hopes to offer updated COVID-19 boosters in the fall that combine the original vaccine with protection against the latest variant.
Now it's reporting a hint that such an approach might work.
Currently, all COVID-19 vaccines are designed to tackle the original coronavirus strain.
But before omicron struck, Moderna began testing a shot combining the original vaccine with protection against an earlier variant named beta.
The company says people who were administered that test combo shot developed more antibodies capable of fighting newer variants — including omicron — than today's regular booster.
Researchers said protection continued six months after the shot was administered.
Studies are underway to see if a combination shot that adds omicron-specific and 31 other mutations protection works better.
Studies of the two boosters are underway.
Results are expected by the end of June.