Moderna Is Developing Two Different Omicron-Targeting Booster Shots

In these countries, Moderna is seeking authorization for the use of mRNA-1273.214, a vaccine that targets both the ancestral strain of the coronavirus and the BA.1 subvariant of Omicron. The BA.1 subvariant was predominant earlier in the year but has been largely displaced by other Omicron subvariants in many countries.

In the U.S., however, Moderna will develop a different dual-target booster, mRNA-1273.222, which goes after both the ancestral strain and the BA.4 and BA.5 subvariants of Omicron. These subvariants, which are nearly identical to each other for the purposes of a vaccine, now account for most new cases of Covid-19 in the U.S.

The subvariants have been spreading rapidly around the U.S. and have been able to partly elude even shots modified to target the original Omicron subvariant that Moderna and other drugmakers have been working on.

Public-health specialists are particularly concerned about BA.5 due to evidence indicating it is highly contagious and carries a high risk of reinfections.

In late June, the U.S. Food and Drug Administration recommended that Moderna and other vaccine makers including

Pfizer Inc.

pursue new booster shots specifically targeting the BA.4 and BA.5 subvariants, as well as the ancestral coronavirus strain.

The FDA may authorize these shots before learning results of any clinical trials of them, instead basing its decision on studies of the booster shots that target the original Omicron strain.

These BA.4/5-targeted shots could be rolled out for a booster campaign in the U.S. starting in early to mid-fall, the FDA said. It would mark the first changes in the composition of the Covid-19 vaccines since they began rolling out in late 2020, designed to target the original strain of the coronavirus.

Moderna said it is following the FDA’s advice by developing the BA.4/5-targeted booster shot.

Yet Moderna had argued that its original Omicron-targeting booster would be sufficient to provide some boost to people’s immunity against the BA.4/5 strains, and that it could make those shots available sooner—later in July or August—than BA.4/5-targeted shots.

Moderna continued to talk up the benefits of the Omicron-targeted booster shot that it started working on earlier this year. The company said that its Omicron-targeted booster shot, mRNA-1273.214, increased people’s immune-system antibodies against BA.4/5 to higher levels than its currently authorized booster shot in a study.

Write to Peter Loftus at peter.loftus@wsj.com