The chances of becoming infected by Covid fell sharply after a first dose of either the AstraZeneca or Pfizer vaccines, a UK study has found.

The vaccines worked just as well in the over-75s and those with underlying health conditions, as other people.

The Office for National Statistics (ONS) and University of Oxford research also found a strong antibody response in all age groups from both jabs.

Everyone showed some response to both vaccines, they said.

The research, contained in two studies which have not yet been peer-reviewed or published, is based on virus tests from 370,000 people in the general UK population - one of the largest to date.

It provides further real-world evidence that the vaccines being used in the UK to protect against Covid-19 are effective at protecting people against coronavirus infections.

In the first study, people who had been vaccinated with a single dose of either the Oxford-AstraZeneca or Pfizer-BioNTech vaccines were 65% less likely to get a new Covid infection.

Three weeks after their jab, given between December 2020 and early April 2021, infections with symptoms fell by 74%, while infections with no reported symptoms fell by 57%.

Those who had received a second vaccine dose of Pfizer were 90% less likely to be infected. The same calculation could not be made for AZ, because too few people in the study had received a second dose as its rollout started later.