One dose of the Pfizer / BioNTech vaccine gives people about 90% protection against Covid for 21 days, according to an analysis by Israel’s mass vaccination program.
The data analysis, conducted by researchers from the University of East Anglia with UK government funding, contradicts an earlier study from Israel which suggested that one dose may not provide adequate protection.
Prof Nachman Ash, head of the Israeli vaccination effort, said last month that a single dose “seems less effective than we thought”, and that it is also lower than what Pfizer suggested. Pfizer said the effectiveness is 52% after a single dose.
Prof Paul Hunter and dr. However, Julii Brainard says that their re-analysis of the data, which was not assessed by peer, shows a high level of protection just before the second dose was given at 21 days. However, they warn that the risk of infection doubled in the first eight days after vaccination – possibly because people became less careful.
The UK has decided to give the second dose of both the Pfizer / BioNTech and Oxford / AstraZeneca vaccines up to 12 weeks after the first dose to maximize the number of protected individuals.
“But this decision has drawn criticism from some quarters, in part because of the belief that a single injection cannot provide adequate immunity,” said Hunter, of the UEA’s medical school in Norwich.
” A recent, non-peer-reviewed preprinted paper, based on Israel’s experience, looked at data from 500,000 people who received the Pfizer vaccine. It reported that a single dose may not provide adequate protection.
‘But we did see a number of flaws in the way they looked at the data, including the fact that from day 18 they were not trying to estimate the effectiveness of the vaccine. This would have given a better indication of how effective a single dose of the vaccine can be if the second dose is delayed by up to 12 weeks. ”
The number of people in Israel increased among those who gave an initial dose, according to them, up to eight days after vaccination, and then decreased.
“Surprisingly, the daily incidence of cases increased sharply after vaccination to about day eight – about doubled. “We do not know why there was this initial increase in the risk of infection, but it may be related to people who are less careful to maintain protective behavior as soon as they receive the injection,” Hunter said.
‘We found that the effectiveness of the vaccine was still around zero until about 14 days after humans were vaccinated. But after day 14, the immunity gradually increased from day to day to about 90% on day 21 and then it did not improve further. All observed improvement was before any second injection.
“It shows that a single dose of vaccine is very protective, although it can take up to 21 days to reach it.”
He believes it should be reassuring for the UK. The researchers do not know how long protection will last after a single shot, he said, but “we are unlikely to see a major decline during the next nine weeks”.