Moderna is considering offering updated COVID-19 boosters in the fall that combine its original vaccine with protection against the Omicron variant.

It reported on Tuesday an early hint that such an approach might succeed.

All COVID-19 vaccines today are based on the original version of the virus.

But this virus continues to mutate, with the latest threat being the highly contagious Omicron variant and its resulting subvariants.

Before Omicron emerged, Moderna was studying multivalent vaccines that added protection against the previous variant called Beta.

On Tuesday, the company said that people given the original Beta-formulated vaccine produced more antibodies capable of fighting many variants including Omicron.

While the increase in antibodies was modest, Moderna’s goal is to produce a combined dose that specifically targets Omicron.

Dr. Jacqueline Miller, Vice President of Moderna, said: “These results really give us hope” that the next step will work better.

Tuesday's data was reported online and has not been reviewed by independent experts.

COVID-19 vaccines still provide strong protection against severe illness, hospitalization, and death, even against Omicron.

This variant is so different from the original virus that it easily bypasses immune defenses, although studies in the US and elsewhere show that an original booster dose enhances protection.

Some countries offer a second booster to people at particularly high risk; in the US, anyone aged 50 or older or those with severe immune deficiency.

Health officials have explained that giving boosters every few months is not the solution for the mutating virus.

They have begun discussing how to determine whether and when the vaccine formula should change.

Simply switching to a vaccine targeting the latest version is risky, because the virus can mutate again.

So, both Moderna and its competitor Pfizer are testing what scientists call “bivalent” shots – a mix of each company’s original vaccine and a version targeting Omicron.

Moderna is now testing a bivalent shot that better targets Omicron, incorporating 32 mutations of this kind.

Studies of two booster doses are underway in the US and Britain; results are expected by late June.