Pharmaceutical and biotechnology companies Pfizer and BioNTech announced Saturday that updated versions of their vaccines that were adapted to the omicron variant of COVID-19 deliver a “substantially higher immune response” against the strain.

Studies “found that a booster dose of both Omicron-adapted vaccine candidates elicited a substantially higher immune response against Omicron BA.1 as compared to the companies’ current COVID-19 vaccine,” according to a press release from the companies, referring to the original omicron variant.

One of the updated vaccines is monovalent, targeting omicron alone, and the other is bivalent, combining the monovalent one with the companies’ vaccine targeting the initial COVID-19 strain.

Both vaccines, when taken as a fourth booster shot, were found to significantly increase neutralization against omicron. The companies said that after the shots were administered, each in two different dosage amounts, the monovalent booster increased that neutralization 13.5- and 19.6-fold and the bivalent increased it 9.1- and 10.9-fold.

The studies were conducted with 1,234 adults aged 56 or older.

The vaccines also “demonstrated a favorable safety and tolerability profile similar to the Pfizer-BioNTech COVID-19 Vaccine,” the companies said.

They added that preliminary laboratory studies showed the updated vaccines performing well against the BA.4 and BA.5 omicron subvariants, though not as well as they were found to against the original omicron variant.

“Omicron has newly evolving sublineages that have outcompeted BA.1 and exhibit a trend of increasing potential for immune escape,” said BioNTech CEO and Cofounder Ugur Sahin. “We will therefore remain vigilant and are prepared to rapidly adapt our Omicron-adapted vaccine candidates to emerging sublineages if epidemiological and laboratory data suggest.”

Pfizer and BioNTech have shared these results with the U.S. Food and Drug Administration (FDA) and European Medicines Agency.

The companies will discuss the data with regulators with the goal of “rapidly introducing [an] adapted booster to address current and future variants,” the press release said.

Discussions with the FDA Vaccines and Related Biological Products Advisory Committee will take place on Tuesday and with the International Coalition of Medicines Regulatory Authorities on Thursday.