London (CNN) – The Oxford / AstraZeneca vaccine would reduce the transmission of the virus, rather than simply reduce the severity of the disease, British researchers suggested.
The number of positive PCR tests decreased by about half after two doses, according to preliminary results from Oxford University researchers who have not yet been peer-reviewed.
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Their analysis, published in advance on Tuesday, also supports dose spacing and estimates good efficacy after a single injection of the Oxford AstraZeneca vaccine.
This is what is known about how the Oxford / AstraZeneca vaccine would reduce transmission
In the study, transmission was not measured directly, for example, by tracking contacts infected by study volunteers. But the researchers regularly collected nasal swabs from some participants who received the Oxford / AstraZeneca vaccine and found that the percentage of positive PCR tests was cut in half after two doses of the vaccine. After a single dose, the percentage of positive tests was reduced by 67%.
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Although transmission studies were not included in the analysis per se, in the UK study, swabs were obtained from volunteers every week, regardless of symptoms, to assess the overall impact of the vaccine on infection risk and thus a surrogate for potential future transmission, ” write the authors.
If the vaccine simply made infections milder, the PCR positivity wouldn’t change, the authors reasoned in the pre-publication analysis. “A measure of overall PCR positivity is useful for assessing whether there is a reduction in infection pressure.”
Vaccine trials with the coronavirus were mainly aimed at preventing symptomatic cases of Covid-19. Previously, there was little public data indicating that vaccines could prevent people from passing the infection on to others.
Data are needed to confirm that the Oxford / AstraZeneca vaccine would reduce transmission
Helen Fletcher, professor of immunology at the London School of Hygiene and Tropical Medicine, told the UK Science Media Center (SMC) that the research data “ suggests that the vaccine may affect transmission, but that this needs to be confirmed later. ».
Dr. Doug Brown, executive chairman of the British Society for Immunology, told SMC the study “indicates that the Oxford / AstraZeneca vaccine may be effective in preventing people from transmitting the virus.”
He added, “While this would be very welcome news, we need more data,” says Brown of whether the Oxford / AstraZeneca vaccine would reduce transmission, “and so it’s important that we all follow the guidelines for continue to monitor social distancing after we get vaccinated ».
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Spread out the vaccine doses
The Oxford / AstraZeneca vaccine was 66.7% effective against symptomatic illnesses that started two weeks after the second injection, according to researchers at the University of Oxford.
The new analysis adds new test sites and a month of new data to the mix, based on previous results announced by AstraZeneca that the vaccine had shown an estimated efficacy of 70.4%.
However, the latest research also suggests that the vaccine can provide significant protection after just one injection.
The study estimates an efficacy of 76% up to three months after a dose. This is based on a subgroup of 88 symptomatic infections, unevenly distributed between the vaccine and placebo groups between 22 and 90 days after vaccination. The study also found relatively stable levels of antibodies during this time period, “with minimal decline at day 90.”
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There may be greater efficacy when the doses are divided
Additionally, the authors suggest there may be greater efficacy with larger doses. In adults aged 18 to 55 years, the efficacy of the vaccine seemed to be increased when the time between injections was delayed from less than six weeks to more than 12. However, more information is needed to understand the statistical significance of that finding.
Taken together, the findings may bolster the UK’s decision to recommend dosages spaced up to 12 weeks apart, according to a statement by Oxford Vaccine Trial lead investigator and paper co-author Andrew Pollard.
“This is positive news as it shows that a single dose of this vaccine generates good immunity and that this protection does not appear to diminish in the short term,” said Brown of the British Society for Immunology.
In terms of immunology, this finding is not unexpected, as we know that some other vaccines confer better immunity when the doses are more divided. While more information is needed to confirm these findings for older age groups, this new research should generally provide reassurance for the UK’s decision to offer the two doses of this vaccine 12 weeks apart.
Comparable data is not yet available on delaying the second dose of the Pfizer / BioNTech vaccine until 12 weeks after the first dose, said Dr. Gillies O’Bryan-Tear, former chair of policy and communications at the College of Pharmaceutical Medicine in a commentary on the SMC. But, he added, “most commentators agree that the same is likely to be true for that vaccine and indeed other two-dose vaccines.”
The authors caution that the studies were not initially designed to assess efficacy by dose intervals, but the data “emerged from the logistics of conducting large-scale clinical trials in a pandemic setting.”
The main analysis is based on 332 symptomatic infections that occurred more than two weeks after their second dose in more than 17,000 trial volunteers in the UK, Brazil and South Africa.
AstraZeneca announced last month that it had completed enrollment for its Phase 3 study in the United States, which will serve as the “primary basis” for the company’s eventual filing with the US Food and Drug Administration.
The vaccine has already been approved in several countries, such as the UK and India, but according to Operation Warp Speed’s Moncef Slaoui, approval will not reach the US until late March at the earliest.