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Risk of Covid plummets 21 days after first vaccine dose, analysis suggests
The chance of getting Covid-19 after being vaccinated drops sharply 21 days following a first dose, new analysis suggests.
People who become infected post-vaccination are also less likely to have symptoms than those who test positive for the virus but who have not been jabbed.
The findings come as Health Secretary Matt Hancock announced that everyone over the age of 18 in England would be able to book a Covid-19 vaccine from Friday.
Speaking at the NHS Confed Conference, Mr Hancock also said a first dose of vaccine had now been given to four out of five adults.
The new analysis on infections has been published by the Office for National Statistics (ONS) and is based on a sample of adults who had received the vaccine up to May 31.
It suggests the risk of infection increases following a first dose, peaking at around 16 days.
There is then a “strong decrease” in risk up to around one month after the first dose, and the risk then declines slowly but steadily.
Rates of infection post-vaccination are likely to be very low, however.
Out of a sample of 297,493 people vaccinated, 1,477 (0.5%) were subsequently found to have a new positive infection of Covid-19.
There was a very slight difference between whether the person had received the Pfizer/BioNTech vaccine (0.8% of the total) and Oxford/AstraZeneca (0.3%).
From a sample of 210,918 adults who had received both doses of vaccine, just 0.1% were subsequently found to have a new positive infection.
Possible explanations for infection shortly after getting the vaccine include someone catching Covid-19 before they had received a jab, or exposure to Covid-19 at a vaccination centre, the ONS said.
The analysis comes as separate figures suggest cases of Covid-19 are “rising exponentially” across England, driven by younger and mostly unvaccinated age groups.
A study commissioned by the Government found infections increased 50% between May 3 and June 7, coinciding with the rise of the Delta coronavirus variant which was first detected in India and is now dominant in the UK.