Pfizer Inc and BioNTech announced on Thursday that their coronavirus vaccine is almost 91% effective at preventing the disease, citing updated trial data that included participants vaccinated for up to 6 months.

The dose was also 100% effective in preventing illness among trial participants in South Africa, where a new variant called B1351 is prevalent, although the number of those participants was relatively small at 800.

While the new overall efficacy rate of 91.3% is lower than the 95% originally reported in November for its 44,000-person trial, a number of variants have become more dominant around the world since then.

The updated results, which include data on over 12,000 people fully inoculated for at least 6 months, position the drugmakers to submit for full U.S. regulatory approval, Pfizer’s Chief Executive Officer Albert Bourla said.

The vaccine is currently authorized on an emergency basis by the U.S. Food and Drug Administration (FDA).

The trial data “provide the first clinical results that a vaccine can effectively protect against currently circulating variants, a critical factor to reach herd immunity and end this pandemic for the global population,” Ugur Sahin, chief executive officer at BioNTech, said in a statement.

Experts fear new variants of the coronavirus from Brazil and South Africa may be resistant to existing vaccines and treatment. According to federal data, more than 300 infections of the South African variant have been detected in over 25 U.S. states and jurisdictions.

The vaccine was 100% effective in preventing severe disease as defined by the U.S. Centers for Disease Control and Prevention and 95.3% effective in preventing severe disease as defined by the U.S. Food and Drug Administration.

There were also no serious safety concerns observed in trial participants up to 6 months after the second shot, the companies said.

They added that it was generally equally effective irrespective of age, gender, race or ethnicity, and among participants with a variety of existing medical conditions.

The trial reviewed more than 900 confirmed cases of the coronavirus, most of which were among participants who received a placebo.

The release of updated results comes on the heels of separate data that revealed the vaccine is safe and effective in 12- to 15-year olds, paving the way for the drugmakers to seek U.S. and European approval to use the dose in this age group within weeks.