Single Pfizer fired 90 percent effectively after 21 days: study

A single dose of the Pfizer vaccine provides ‘very high’ protection against COVID-19 after 21 days – without a ‘supplemental’ dose within the recommended time frame, according to a new study from the University of East Anglia.

Researchers looked at data from Israel, where the vaccine was rolled out.

They found that the Pfizer vaccine becomes 90 percent effective after 21 days, which supports UK plans to delay the timing of a second injection.

But they warn that people’s risk of infection has doubled in the first eight days after vaccination – possibly because people become less careful.

Due to the rapid response of this research, it has not yet been judged by peers.

Principal researcher and COVID-19 expert, prof. Paul Hunter, from UEA Norwich Medical School, said: ‘A second dose of the Pfizer vaccine is usually given 21 days or more after the first to increase the effect of the first dose.

‘But here in the UK, the decision has been made to postpone the timing of the second injection to 12 weeks after the first.

‘The logic behind this is to protect more people sooner and thus reduce the total number of serious infections, hospitalizations and deaths.

‘But this decision has drawn criticism from some quarters, in part because of the belief that a single injection cannot provide adequate immunity.

“A recent, non-peer-reviewed, predetermined paper, based on Israel’s experience, looked at data from 500,000 people who received the Pfizer vaccine. It is reported that a single dose may not provide adequate protection.

“But we saw a number of errors in how they looked at the data, including the fact that from day 18 they did not try to estimate the efficacy of the vaccine. This would have given a better indication of how effective a single dose of the vaccine was. Vaccination may be if the second dose is delayed by up to 12 weeks. ‘

The research team tried to estimate the effectiveness of the Pfizer vaccine after a single dose – by re-analyzing the actual results from Israel.

They use the data to see how the Israeli vaccination program affects the numbers on the effects, and continue to estimate the effectiveness of the vaccine over time.

They found that the numbers increased after eight days after the initial vaccination before dropping to low levels by day 21.

Prof Hunter said: “Surprisingly, the daily incidence of cases increased sharply after vaccination to about day eight – about doubling. We do not know why this initial increase was in risk of infection, but it may be related to the fact that people are less careful with maintenance is protective behavior as soon as the injection takes place.

“We found that the effectiveness of the vaccine was still about zero until about 14 days after people were vaccinated. But after day 14, the immunity gradually increased from day to day to about 90 percent on day 21 and then it did not improve further. All the 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.

‘And it supports UK policy to widen the gap between doses by showing that a single dose can provide a high level of protection.

“Although we do not know how long this immunity will last longer than 21 days without a second stimulation, we are unlikely to see any deterioration during the next nine weeks,” he added.

Prof Hunter and dr. Brainard was funded by the National Institute for Health Research Health Protection Research Unit (NIHR HPRU) in emergency preparedness and response at King’s College London in collaboration with Public Health England (PHE) in collaboration with the University of East Anglia.

“Estimating the effectiveness of the Pfizer COVID-19 BNT162b2 vaccine after a single dose. A re-analysis of a study of ‘actual’ vaccination outcomes from Israel is published on the medRxiv preprinted server: www.medrxiv.org/content/10.110… 021.02.01.21250957v1