Researchers have identified that a single dose of the AstraZeneca (AZ)/Oxford University or the Pfizer/BioNTech vaccines can ‘significantly’ reduce the risk of COVID-19 infection.
Across two studies, published on the pre-print server medRxiv last week, researchers analysed over 1.6 million test results taken from over 370,000 study participants between 1 December 2020 and 3 April 2021 in the UK.
In one study, researchers found that a single dose of either the AZ/Oxford or Pfizer/BioNTech vaccine cut the risk of all new COVID-19 infections by 65%, also reducing symptomatic infections by 72% and infections without reported symptoms by 57%.
In addition, individuals who had received a second dose of the Pfizer/BioNTech vaccine saw their risk of infection cut by 90%.
The researchers also reported that the vaccines were effective against variants comparable to the UK variant – B.1.1.7 – with similar benefits from the vaccines in reducing new infections in both older individuals (aged 75 years and older) and those under the age of 75 years old.
A second study compared the changes in antibody levels following a single dose of either the AZ/Oxford or Pfizer/BioNTech vaccines, or two doses of the Pfizer/BioNTech vaccine.
In this study, researchers identified a lower antibody response to a single dose of either vaccine in older individuals who had not had COVID-19 previously.
However, antibody responses to two doses of the Pfizer/BioNTech vaccine were ‘high’ across all age groups, with increasing responses in older adults reaching similar levels to those receiving a single dose after prior COVID-19 infection.
The researchers also discovered that antibody levels increased more slowly and to a lower level with one dose of the AZ/Oxford vaccine, although they decreased at a faster rate after a single Pfizer/BioNTech dose, particularly in older adults.
The studies were based on data from the COVID-19 Infection Survey, which is a partnership between Oxford University, the Office of National Statistics (ONS) and the Department for Health and Social Care (DHSC).
“Without large community surveys such as ours, it is impossible to estimate the impact of vaccination on infections without symptoms – these have the potential to keep the epidemic going, particularly if people who have been vaccinated mistakenly think they cannot catch COVID-19,” said Sarah Walker, chief investigator and academic lead for the COVID-19 Infection Survey.
“However, these studies show that vaccination and previous infection both protect against getting infected again. We don’t yet know exactly how much of an antibody response is needed, and for how long, to protect people against getting COVID-19 in the long term – but over the next year, information from the survey should help us to answer these questions,” she added.