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The results were shared in a news release and have not yet been peer-reviewed or published.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.