A single dose of vaccine reduces infection rate by 65%, study finds

April 26, 2021: – A single dose of Oxford-AstraZeneca or Pfizer-BioNTech’s Covid-19 vaccine reduces the risk of infection in adults of all ages drastically, British researchers have found.

Two studies released on Friday analyzed over 1.6 million nose and throat swabs were 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 Office of National Statistics, and the Department for Health and Social Care of the U.K.

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, fell 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.

Vaccines had a similar effect in adults of all ages when it came to reducing infection rates; the study found their ability to reduce infections also identical regardless of whether participants had long-term health conditions.

Scientists also examined the impact Covid vaccinations had on participants’ antibody levels.  They found that older adults significantly above 60 who had never contracted Covid had a lower immune response to a single vaccine dose than those infected with the virus before.

Antibody responses to two doses of the Pfizer-BioNTech vaccine were high across all age groups. Data showed that older adults could reach similar antibody levels to those who had received one vaccine dose after a previous Covid infection.

Antibody levels rose more slowly following a single dose of the Oxford-AstraZeneca vaccine than the Pfizer-BioNTech alternative. However, antibody levels dropped more quickly following an amount of the latter, particularly in older adults, so that patients reached similar levels of antibodies to those seen after a first shot of the Oxford-AstraZeneca vaccine.