The Pfizer vaccine for Covid-19 in older people is nearly 95 per cent effective, the pharmaceutical company announced as it released more data from its clinical trials.
The news paves the way for the company to apply for emergency authorisation of the vaccine in the US within days.
Pfizer and its partner BioNTech said their vaccine protected people of all ages and ethnicities, with no significant safety problems so far in a trial with almost 44,000 participants.
The update is the latest in a string of promising developments on the vaccine front in recent days. Moderna's rival vaccine appears equally effective, judging from data published earlier this week, and a third contender, from Oxford University and AstraZeneca, is expected to release trial results in the coming days.
The Pfizer data shows 170 trial participants caught Covid-19 overall.
Eight participants who received the vaccine fell ill, while 162 cases were seen among those who had the placebo.
The shot helped to prevent severe disease, according to the analysis, with nine of 10 severe cases in the trial occurring in the placebo group.
The vaccine’s efficacy in people older than 65 was more than 94 per cent, the companies said.
The figure is slightly higher than initial results showing the Pfizer vaccine was 90 per cent effective.
Most people who received the shot tolerated it well.
Severe fatigue was seen in 3.7 per cent of volunteers after the second dose in the two-shot regimen, but that was the only severe side effect that occurred in more than 2 per cent of people, according to the analysis.
The companies said that the safety milestone required by the US Food and Drug Administration for emergency authorisation had been achieved.
“The study results mark an important step in this historic eight-month journey to bring forward a vaccine capable of helping to end this devastating pandemic. We continue to move at the speed of science to compile all the data collected thus far and share with regulators around the world,” said Pfizer's chief executive, Dr Albert Bourla.
“With hundreds of thousands of people around the globe infected every day, we urgently need to get a safe and effective vaccine to the world.”
Meanwhile, the companies tried to address concerns over the deep-freezer conditions needed for the vaccine.
Most GP clinics do not have the capacity to store the vaccine at -70C.
Pfizer and BioNTech said they had developed "specially designed, temperature-controlled thermal shippers utilising dry ice to maintain temperature conditions" which can be used for up to 15 days by refilling with dry case.
Each container would have a GPS thermal sensor to track location and temperature as it makes its way across the world.