A single dose of Oxford-AstraZeneca or Pfizer-BioNTech’s Covid-19 vaccine drastically reduces the risk of infection in adults of all ages, British researchers have found.
Two studies released on Friday analyzed more than 1.6 million nose and throat swabs taken from 373,402 people between December and April. The data was collected as part of the ongoing Covid-19 Infection Survey, carried out by the University of Oxford, the U.K.‘s Office of National Statistics and the U.K.’s Department for Health and Social Care.
Researchers found that 21 days after a single dose of either the Oxford-AstraZeneca or the Pfizer-BioNTech vaccine, new Covid infections — both symptomatic and asymptomatic — had fallen by 65%.
Symptomatic infections fell by 74% three weeks after a single dose of either vaccine, while asymptomatic cases were down by 57%, the data showed.
A second vaccine dose reduced the overall infection rate by 70%, with symptomatic Covid infections down by 90% and asymptomatic cases of the virus cut by 49%.
Researchers likened these effects to the natural immunity gained from being infected with the virus.
However, they warned that the fact that vaccinated individuals could still be infected — even if those infections were predominantly asymptomatic — meant “onward transmission remained a possibility.”
Vaccines had a similar effect on adults of all ages when it came to reducing infection rates, the study found, with their ability to reduce infections also similar regardless of whether or not participants had long-term health conditions.