A single shot of the Pfizer/BioNTech vaccine could be more potent in protecting against Covid-19 than first thought, Israeli scientists said.
Statistics showed more than 90 per cent of people who received the first does had a major response in building up immunity to the coronavirus.
The discovery could help with the struggle to supply second doses of the vaccine, with global supplies running short, the Financial Times reported on Friday.
The Pfizer/BioNTech vaccine requires two injections for people to obtain the full benefit.
The first shot helps the immune system to create a response to Covid-19. This is followed up by a second injection at a later date to boost the immune system and provide long-term protection.
More than 90 per cent of the 1,800 doctors and nurses who received the two dose vaccine, at the Rambam Health Care Campus in Israel, showed major levels of antibodies 21 days after the first shot and before they received their second injection.
“If 93 per cent had a major response three weeks after the first injection, this raises a good question, that you might rather be using the first injection on more people,” said Dr Michael Halberthal, chief executive of the hospital.
Another hospital in Israel, the Sheba Medical Centre, showed at least 50 per cent of staff had a level of antibodies "above the cut-off point" two weeks after the first dose.
These findings could provide encouragement to scientists arguing to extend the time between the first and second doses of the vaccine, to give more people some form of protection before beginning the second phase of inoculations.
Pfizer/BioNTech hopes two doses of its vaccine will give up to 95 per cent protection against Covid-19. But a less effective one could be the difference between survival and death.
Experts pointed to the flu shot, which is about 40 to 60 per cent effective but has proven crucial in saving lives and taking pressure off healthcare services.
It comes as governments eager to increase vaccinations against Covid-19 have been faced with delayed deliveries of crucial shots. Pfizer/BioNTech has already given a warning about an immediate slowdown in deliveries as it makes adjustments to production plants.