Single dose of Pfizer-BioNTech or Oxford-AstraZenca vaccine reduces infection rate by 65%, study finds

A study by British researchers has found that the risk of Covid-19 infection in adults of all ages is drastically reduced by a single dose of Oxford-AstraZeneca or Pfizer-BioNTech’s Covid-19 vaccine.

More than 1.6 million nose and throat swabs taken from 373,402 people between December and April were analysed in two studies released on Friday. These studies were a part of the ongoing Covid-19 Infection Survey that is being carried out by University of Oxford, the UK’s Office of National Statistics and the UK’s Department for Health and Social Care.

There was a drop of 65 per cent in new Covid infections — both symptomatic and asymptomatic, after 21 days of a single dose of either the Oxford-AstraZeneca or the Pfizer-BioNTech vaccine, researchers found.

The data also showed that there was a 57 per cent drop in asymptomatic cases, and 74 per cent drop in symptomatic infections three weeks after a single dose of either of the vaccines.

The overall infection rate was reduced by 70 per cent while symptomatic and asymptomatic Covid-19 infections were down by 90 per cent and 49% respectively after a second vaccine dose.

The natural immunity gained from being infected with the virus was identified as the reason for this by the researchers.

But “onward transmission remained a possibility” because those people who have been vaccinated could still be infected, even if such infection were mostly asymptomatic, the researchers warned.

The study also found that with respect to reducing infection rates, there was a similar effect of the vaccines in adults of all ages. Also the ability of both the vaccines was also similar with respect to reducing infections irrespective of whether or not the inoculated individuals had a history of long-term health conditions.

The impact of the Covid-19 vaccines on participants’ antibody levels were also examined by the researchers and scientists.

The studies found that there was a lower immune response to a single vaccine dose for those older adults who had never contracted Covid-19 – particularly those who were more than 60 years of age, compared to those who had been infected by the virus.

Data showed that irrespective of age, there were high antibody responses to two doses of the Pfizer-BioNTech vaccine which means that similar antibody levels could be reached by older adults compared to those who had received one vaccine dose after previous Covid-19 infection.

Researchers also could not assess the impact on antibody response for the Oxford-AstraZeneca vaccine because too few people had received two doses of the vaccine in the UK.  The researchers however noted that the immune responses to a first dose were different for the Oxford-AstraZeneca and the Pfizer-BioNTech vaccines.

There was no group that did not respond to either of the vaccines even though there were differences to the immune responses depending on the age groups. The study also found a small section of the people – less than 5 per cent, showed low immune responses to both the vaccines.

(Adapted from


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s