The UN health agency says there is no causal link between the AstraZeneca vaccine and blood clots.
Pfizer Inc and BioNTech said new clinical trial data signalled that their COVID-19 vaccine could protect against the new coronavirus variant first discovered in South Africa.
The shot was 100 percent effective in preventing illness among trial participants in South Africa, where the new B1351 coronavirus variant is dominant, the companies said. The South Africa trial was relatively small, with 800 participants.
Pfizer said the rate was derived from a relatively small number of nine infections observed, all in the placebo group.
Separately, the companies said their vaccine is approximately 91 percent effective at preventing COVID-19, citing updated trial data that included participants inoculated for up to six months.
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’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 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 have feared new variants of COVID-19 from South Africa and Brazil may be resistant to existing vaccines and treatment.
Lab tests have previously indicated that BioNTech’s vaccine was less potent but still offered a robust defence 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 a later market release 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 updated trial data showed that of 927 confirmed COVID-19 cases detected through March 13, 77 were among people who received the vaccine and 850 were among people who got dummy shots.
The vaccine is currently authorised on an emergency basis by the US Food and Drug Administration.
“Initially, people thought the vaccine was good for 90 days, so the fact that Pfizer came out and said, ‘No, you’ll get 91 percent protection after six months’ is very good news,” said Al Jazeera’s Alan Fisher, speaking from Washington, DC.
“It extends the period that people can get vaccinated and who then may need a booster jab.”
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.
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.
‘Vaccinations highly likely to protect us’
Sterghios Moschos, an associate professor at Northumbria University, said the latest development regarding the ability of the vaccine to protect people is “really good news”.
“The fact that it is working for six months is fantastic because that means it gives us a longer window to look into these new variants,” he told Al Jazeera.
The way that efficacy is calculated, he explained, is that people come out of these test programmes showing symptoms. They then get tested and try to find out whether they received the vaccine or the placebo.
“What’s happened in this case is that six months after the study has started, the evidence showed that the people who have developed symptoms of COVID-19 are actually people that have not received the vaccine in the vast majority,” he said.
“It means in society, out of 10 people who get the disease, nine would be individuals who have not been vaccinated, and therefore, vaccinations are highly likely to protect us.”