The drug-making company says their shot was also 100 percent effective in preventing illness among trial participants in South Africa, where a new variant called B1351 is dominant, though the number of those participants was relatively small at 800.
Pfizer Inc and BioNTech’s Covid-19 vaccine has shown around 91 percent efficacy at preventing the disease in recently released updated trial data that included participants inoculated for up to six months.
The shot was also 100 percent effective in preventing illness among trial participants in South Africa, where a new variant called B1351 is dominant, though the number of those participants was relatively small at 800.
While the new overall efficacy rate of 91.3 percent is lower than the 95 percent originally reported in November for its 44,000-person trial, a number of variants have become more prevalent around the world since then.
Pfizer Chief Executive Albert Bourla said the updated results, which include 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.
High percentage effectiveness
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,” BioNTech Chief Executive Ugur Sahin said in a statement.
Experts fear that new variants of Covid-19 from South Africa and Brazil could 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, federal data shows.
The vaccine was 100 percent effective in preventing severe disease as defined by the US Centers for Disease Control and Prevention and 95.3 percent 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.
"These data reinforce our view that we have some really potent vaccines," said Danny Altmann, a professor of immunology at Britain's Imperial College London, who was not involved in the Pfizer trial.
He said the effectiveness against the South African variant was "especially noteworthy," since it showed the vaccine is likely to offer effective protection in real-world settings where several different coronavirus variants could be circulating.
The trial reviewed more than 900 confirmed cases of Covid-19, most of which were among participants who received a placebo.
Jabs for under-16s
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.
Israel also hopes to administer the Pfizer-BioNTech coronavirus vaccine to children aged 12 to 15 from May, after a study showed its efficacy for the age group, health officials said.
Israel has already given the two recommended shots of the Pfizer-BioNTech vaccine to more than half of its 9.3 million residents, the world's leading pace per capita.
It has offered inoculations to all residents 16 and above, the group currently approved to get the vaccine.
Speaking to Israel's army radio on Thursday, Health Ministry Director General Hezi Levy said the ministry wanted to begin inoculating under-16s as early as May.
"We are seeing a rise in the number of children who are hospitalised, and we are seeing children without symptoms but who suffer from complications," Levy said.
"The risk from the vaccine is much lower."
The head of Israel's pandemic response task-force, Nachman Ash, told Kan radio that health officials wanted the US Food and Drug Administration to extend its approval to the lower age group.
After FDA approval, it would be then discussed by Israel's vaccination team before the vaccinating of adolescents begins, Ash said.
"I think it will take a few more weeks," he said.