Early signs suggest the UK strategy of delaying the second Covid-19 jab was the right decision, a top Government vaccine adviser has said.
Professor Anthony Harnden, deputy chairman of the Joint Committee on Vaccination and Immunisation (JCVI), said he is "absolutely convinced" that it will turn out to have been the right move.
Other medical professionals have criticised the delay, and the World Health Organisation (WHO) has said the second dose of the Pfizer/BioNTech jab should only be delayed for up to six weeks.
But experts in the UK said that the second jab can be delayed for up to 12 weeks in a bid to get more people vaccinated sooner.
Prof Harnden, who is also professor of primary care at the University of Oxford, said that delaying the second dose means that a greater number of people will receive a first dose and therefore more lives could be saved.
Speaking on a Royal Society of Medicine webinar, he said: "By our calculations, assuming 80-90% of vaccine effectiveness in the over 80s, we calculated that we could save between 3,000 and 4,000 extra lives for every million first doses that we gave.
"And so given the dire situation around the country at the moment with, you know, having exceeded the 100,000 grim deaths statistic, (we) really felt that we could save many, many more thousands of elderly people's lives by this strategy.
"And interesting enough, I've just come off JCVI and we're looking at these real time vaccine effectiveness figures, it's really early stages yet, but it does look like our first dose strategy is proving to be a good one.
"And the early signs are very promising from the data that we've made the right decision on this."
Prof Harnden said the JCVI has acted "nimbly, quickly and promptly" to make a "bold decision" based on the data they have seen.
He said he predicts that the WHO will come round to the UK's delayed second dose strategy.
"I think that won't be too long before that happens.
"And so the more that we see that data reassuring us that we're making the right decision the more likely it is that WHO will come into line," he said.
Prof Harnden said the decision has been taken on a "really clear" basis of the data and a population perspective, adding: "I think it will turn out to be the right decision.
"I'm absolutely convinced it will turn out to be the right decision.
"But we are reviewing this every single week."
Eleanor Riley, professor of immunology and infectious disease at the University of Edinburgh, said she wanted to warmly congratulate the JCVI on what she described as a "very bold" decision and spoke of the importance of people getting the second dose.
"As an immunologist, the data suggests that the second dose is really important.
"The boost you get to your immune system after the second dose is huge," she said, adding: "The first dose will get them through 12 weeks, I'm fairly confident about that, but in order to get that long-lasting protection people do have to come back.
"So I would plead with the people rolling out the vaccine not to delay it past 12 weeks."
Prof Riley said there is data from other vaccines where a delayed second dose was "hugely beneficial", adding: "I think there's theoretical reasons to think that a delayed dose is better.
"I think there is also practical evidence that a delayed dose is no worse, and may be better.
"And I think the data that we've seen so far from the pre-clinical studies looking in detail at the T-cell and antibody responses suggests that there's no dropping off a cliff of the response in the first few weeks after vaccination that would give us cause for concern," she said.
