James Shaw, 82, receives the University of Oxford / AstraZeneca COVID-19 vaccine from specialist nurse Justine Williams, at the Lochee Health Center in Dundee, Scotland, Great Britain on January 4, 2021.
Andy Buchanan | Reuters
LONDON – A single dose of Covid-19 vaccine from Oxford-AstraZeneca or Pfizer-BioNTech drastically reduces the risk of infection in adults of all ages, British researchers have found.
Two studies published Friday analyzed more than 1.6 million nasal 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 conducted by the University of Oxford, the UK’s Office of National Statistics and the UK’s Department for Health and Social Care.
The researchers found that 21 days after a single dose of the Oxford-AstraZeneca or Pfizer-BioNTech vaccine, new Covid infections, both symptomatic and asymptomatic, had decreased by 65%.
The data showed that symptomatic infections decreased by 74% three weeks after a single dose of either vaccine, while asymptomatic cases decreased by 57%.
A second dose of the vaccine reduced the overall infection rate by 70%, with symptomatic Covid infections by 90% and asymptomatic cases of the virus reduced by 49%.
The researchers compared these effects to the natural immunity obtained 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 that “continued transmission remained a possibility.”
Vaccines had a similar effect in 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 participants had health conditions or not. long-term.
What about antibody resistance?
Scientists also looked at the impact of Covid vaccinations on participants’ antibody levels.
They found that older adults, particularly those over the age of 60, who had never contracted Covid had a lower immune response to a single dose of the vaccine than those who had previously been infected with the virus.
The data showed that antibody responses to two doses of the Pfizer-BioNTech vaccine were high across all age groups, which means that the elderly were able to achieve similar antibody levels to those who had received a vaccine dose after a previous Covid infection.
Too few people had received two doses of the Oxford-AstraZeneca vaccine in the UK for researchers to assess its impact on the antibody response. However, immune responses to a first dose were noted to differ between the Oxford-AstraZeneca vaccine and the Pfizer-BioNTech vaccine.
Antibody levels rose more slowly after a single dose of the Oxford-AstraZeneca vaccine than the Pfizer-BioNTech alternative – however, antibody levels fell more rapidly after a dose of the latter, particularly in the elderly, so that patients achieved levels of antibodies similar to those seen after a first shot of the Oxford-AstraZeneca vaccine.
Although immune responses differed between the age groups, the scientists pointed out that there was no group that did not respond to either vaccine. However, a small number of people – less than 5% – had a low immune response to both vaccines.
It is important to receive the second dose
The Oxford-AstraZeneca vaccine has been approved for use in the UK, India and several other countries, but has undergone temporary suspensions in some markets for concerns that it could be linked to rare blood clots. Global health officials said the benefits of administering the vaccine continue to outweigh the risks.
WHO recommends an interval of eight to 12 weeks between the first and second dose of the Oxford-AstraZeneca vaccine.
The Pfizer-BioNTech vaccine is also administered in multiple countries, including the United States. The U.S. Centers for Disease Control and Prevention recommend receiving a second dose of the vaccine three weeks after the first.
In February, the UK launched a trial to see if the mixed doses of the Oxford-AstraZeneca and Pfizer-BioNTech vaccines could be effective.
Sarah Walker, a professor of medical statistics and epidemiology at Oxford University and chief investigator and academic director of the Covid-19 Infection Survey, said on Friday that scientists were still unsure how much of the antibody response and for how long it was needed for long-term protection against Covid.
David Eyre, an associate professor at the Big Data Institute at the University of Oxford, added that the results published on Friday highlighted the importance of receiving a second dose of the vaccine for added protection.