A COVID-19 vaccine developed by Sanofi SA and GSK PLC to target the beta strain of the virus produced a stronger antibody response against variants of omicron when given as a booster compared with certain first-generation shots, two studies have found.

The results are the latest indication that tweaking vaccines can nudge antibody responses in the direction of new variants, possibly helping to shore up immunity as the virus mutates. The study results may also provide an opportunity for Sanofi SAN, -1.03% SNY, -1.94% and GSK GSK, GSK, -2.97%, two vaccine giants that were late to develop COVID-19 immunizations, to play a role in providing booster shots.

In the studies, the beta-targeted vaccine induced a stronger antibody response to certain omicron variants than first-generation vaccines, according to Sanofi. One study compared the beta-targeted vaccine to the original vaccine produced by Pfizer Inc. PFE, -4.12% and BioNTech SE BNTX, -7.11%. Neither study has yet been peer-reviewed.

In a study comparing a booster of the Sanofi-GSK Beta-targeted vaccine with the companies’ original shot, the tweaked vaccine induced double the number of neutralizing antibodies against omicron BA.1 and BA.2 than the older version, Sanofi said Monday. The study, run by the companies, involved around 1,500 people who had received either the Pfizer or Moderna Inc. MRNA, -7.86% vaccines as their primary course of vaccination.

A separate, smaller study run by French researchers compared the Beta-variant Sanofi-GSK vaccine to either the older Sanofi-GSK shot or the Pfizer vaccine as a booster in people who had received two doses of the Pfizer shot. It found that a booster of the beta-variant shot produced higher levels of neutralizing antibodies against the omicron BA.1 variant than either of the other two. That study, which involved 247 people, was funded by the French government and Sanofi.

An expanded version of this report appears on WSJ.com.

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