(CNN) Two Pfizer and BioNTech Covid-19 vaccine boosters updated to target the Omicron variant show a substantially higher immune response than the current Covid-19 vaccine, the companies said Saturday.
The companies tested a vaccine that targets Omicron BA.1 subvariant and bivalent booster -- which targets two strains -- that includes the current Pfizer/BioNTech Covid-19 vaccine and a vaccine candidate that targets Omicron.
The study looked at two different dose levels -- 30 micrograms and 60 micrograms -- in more than 1,200 adults age 56 and older. The current primary and booster dosage for this age group is 30 micrograms.
The study showed that, across both dose levels, a fourth booster with the Omicron-modified vaccine candidates resulted in a substantially higher immune response against the variant. One month after the shot, the monovalent vaccine showed a 13.5- and 19.6-fold increase in Omicron-fighting antibodies, depending on the dose. The bivalent vaccine showed a 9.1 and 10.9-fold increase in antibodies.
Preliminary results from studies in the lab also suggest the vaccines could neutralize the Omicron BA.4 and BA.5, the companies said. The BA.4 and BA. 5 subvariants are increasingly circulating in the United States.
Both vaccine candidates appeared to be safe and well-tolerated.
The results were shared in a news release and have not yet been peer-reviewed or published.
"Based on these data, we believe we have two very strong Omicron-modified candidates that elicit a substantially higher immune response against Omicron than we've seen to date," Pfizer Chairman and Chief Executive Officer Albert Bourla said in a news release.
Earlier this month, Moderna reported its bivalent Covid-19 vaccine booster that contained a vaccine targeting Omicron showed a stronger immune response against the variant. The company said its updated booster also showed a "potent" response against the BA.4 and BA.5 subvariants.
The companies will present their data on Tuesday, when the US Food and Drug Administration's Vaccines and Related Biological Products Advisory Committee meets to vote on updated coronavirus vaccines for the fall.