Advisors to the U.S. Food and Drug Administration are scheduled to meet on Tuesday to discuss whether to update COVID-19 vaccines for the fall. The updated shots are likely to be redesigned to combat the Omicron variant of the coronavirus, experts say.

Pfizer and BioNTech said that 30 and 60 microgram doses of a shot targeting just the BA.1 Omicron subvariant that was circulating last winter elicited a 13.5 and 19.6-fold increase in neutralizing geometric titers against that subvariant. A version of the shot that contained both the redesigned vaccine and their original vaccine elicited a 9.1 and 10.9-fold increase, they said.

The results were from a trial of 1,234 people aged 56 or older. The shots were well-tolerated in participants, the companies said.

They said that early laboratory studies suggest that both Omicron-modified candidates neutralize the Omicron BA.4 and BA.5 subvariants that have been circulating more recently, though to a lesser extent than they do for BA.1, with titers approximately 3-fold lower. The companies say they are continuing to collect data on how well the boosters perform versus the more recently circulating strains.

Moderna Inc MRNA.O has also made a redesigned vaccine targeting the BA.1 Omicron subvariant. The company said its updated vaccine worked well against more recent Omicron subvariants, and that it was moving forward with plans to ask regulators for approval. 

By Michael Erman

(Reporting by Michael ErmanEditing by Nick Zieminski)