Covid risk ‘plummets 21 days after first dose’

LONDON: 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 have been published by the Office for National Statistics (ONS) and are based on a sample of adults who had received the vaccine up to May 31.

They suggest 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 per cent) 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 per cent of the total) or Oxford/AstraZeneca (0.3 per cent).

From a sample of 210,918 adults who had received both doses of vaccine, just 0.1 per cent 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 per cent 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.

Data from nearly 110,000 swab tests carried out across England between May 20 and June 7 suggests Covid-19 cases are doubling every 11 days, with the highest prevalence in north-west England and one in 670 people infected.

Coronavirus restrictions in England have now been formally extended until July 19, following a vote in the House of Commons on Wednesday.