Pfizer Inc and BioNTech said on Thursday, April 1, their COVID-19 vaccine is around 91% effective at preventing the disease, citing updated trial data that included participants inoculated for up to six months.

The shot was also 100% effective in preventing illness among trial participants in South Africa, where a new variant called B1351 is dominant, although that rate was derived from a relatively small number of nine infections observed there, which were all in the placebo group, Pfizer said.

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 prevalent around the world since then.

Pfizer’s Chief Executive Officer Albert Bourla said the updated result, which includes data on more than 12,000 people fully inoculated for at least six months, positions the drugmakers to submit for full US regulatory approval.

The vaccine is currently authorized on an emergency basis by the US Food and Drug Administration.

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 COVID-19 from South Africa and Brazil may be resistant to existing vaccines and treatment. More than 300 cases of the South African variant have been detected in more than 25 US states and jurisdictions, according to federal data.

Lab tests have previously indicated that BioNTech’s vaccine was less potent but still offered a robust defense against the B1351 variant that first emerged in South Africa.

Still, BioNTech reiterated this week there would likely be a future need for booster shots that specifically address new variants and that the group was preparing to upgrade its vaccine when needed.

BioNTech has said that it started testing a modified vaccine version against the South African mutant in March for early indications on safety and efficacy but a product for later market launch would require yet another redesign and more tests.

The updated trial data would not prompt the company to change that development strategy, a BioNTech spokeswoman said.

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

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

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

The trial reviewed more than 900 confirmed cases of COVID-19, most of which were among participants who received a placebo.

The release of updated results comes on the heels of separate data that showed the vaccine is safe and effective in 12- to 15-year olds, paving the way for the drugmakers to seek US and European approval to use the shot in this age group within weeks. – Rappler.com