One dose of Pfizer/BioNTech Covid-19 vaccine gives ‘90% immunity’ after 21 days

New analysis shows that the first dose of the Pfizer/Biontech vaccine provides more protection from Covid-19 than initially thought. Data analysis of Israel's mass vaccination programme, carried out by researchers from the University of East Anglia with UK government funding, shows that one jab gives people as high as 90 per cent immunity from the virus. These new findings contradict Pfizer's initial prediction that one dose would not give people people higher than 52 per cent protection. But UEA professors Paul Hunter and Dr Julii Brainard now say reevaluation of the data shows the Pfizer vaccine gives a high level of protection on the 21st day after the first jab. They also warn the risk of infection doubled in the first eight days following the first jab, but this is more likely to be a result of people becoming less cautious in the first week after receiving the jab. In the UK, the government have decided to leave a three month gap between the first and second doses of the Pfizer vaccine as well as the AstraZeneca vaccine. This prompted criticism amid fears the first dose would not provide sufficient protection for long enough, but a recent study shows the AstraZeneca jab gives 76 per cent protection for the full 12 week time frame. But Hunter, of UEA's medical school, said: "A recent non peer-reviewed pre-print paper based on Israel’s experience looked at data from 500,000 people who had been given the Pfizer vaccine. It reported that a single dose may not provide adequate protection.

"But we saw a number of flaws in how they looked at the data including the fact that they did not attempt to estimate the effectiveness of the vaccine from day 18 onwards. This would have given a better indication of how effective a single dose of the vaccine could be if the second dose was delayed by up to 12 weeks."

"Surprisingly, the daily incidence of cases increased strongly after vaccination till about day eight – approximately doubling. We don’t know why there was this initial surge in infection risk but it may be related to people being less cautious about maintaining protective behaviours as soon as they have the injection," said Hunter.

"We found that the vaccine effectiveness was still pretty much zero until about 14 days after people were vaccinated. But then after day 14 immunity rose gradually day by day to about 90% at day 21 and then didn’t improve any further. All the observed improvement was before any second injection.

"This shows that a single dose of vaccine is highly protective, although it can take up to 21 days to achieve this."