The rate of positive PCR tests decreased by about half after two doses, according to preliminary results by researchers at Oxford University who have not yet been evaluated by peers.
The study did not directly measure the transmission – for example, by locating contact persons who were infected by study volunteers. However, the researchers did collect regular nasal swabs from some participants and found that the rate of positive PCR tests dropped by half after two doses of the vaccine. After only one dose, the percentage of positive tests decreased by 67%.
“While transmission studies per se were not included in the analysis, swabs in the UK study were obtained weekly from volunteers, regardless of the symptoms, to further the overall impact of the vaccine on the risk of infection and thus a substitute for the potential. to determine “transfer,” the authors write.
If the vaccine merely alleviates infections, PCR positivity will not change, the authors argued in the pre-pressure analysis. “A measure of overall PCR positivity is appropriate to determine if there is a reduction in the burden of infection.”
Vaccination trials with the Coronavirus looked primarily at the prevention of symptomatic cases of Covid-19. Previously, there was little other public data suggesting that vaccines can prevent people from transmitting the infection to others.
Helen Fletcher, professor of immunology at the London School of Hygiene and Tropical Medicine, told the UK’s Science Media Center (SMC) that the data in the study ‘suggested a possibility that the vaccine could have an impact on transmission. , but further may follow: up would be necessary to confirm this. “
Dr. Doug Brown, chief executive of the British Society for Immunology, told the SMC that 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 information before it can be confirmed, and therefore it is important that we all continue to take social distance after we have been vaccinated.”
Dose spacing
Researchers at Oxford University said the vaccine had shown 66.7% effectiveness against symptomatic diseases, two weeks after the second shot.
The new analysis adds new trial plots and a month of new data to the blend, building on earlier results that AstraZeneca announced that the vaccine showed an estimated efficacy of 70.4%.
However, the latest research also suggests that the vaccine can provide significant protection after a single shot.
The study estimates 76% efficacy up to three months after one dose. It is based on a subset of 88 symptomatic infections, unequally 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 period, “with a minimal decrease by day 90.”
Furthermore, the authors suggest that higher efficiencies may be associated with higher doses. Among adults aged 18 to 55 years, it appears that the effectiveness of the vaccine increases when the time between shots is spread from less than six weeks to more than 12. However, more information is needed to know how statistically different the finding is.
Taken together, the findings could bolster the UK’s decision to keep doses up to 12 weeks apart, according to a statement from the Oxford Vaccine Trial’s lead investigator and co-author of the article, Andrew Pollard.
“This is positive news, as it shows that just one dose of this vaccine produces good levels of immunity and that protection in the short term does not seem to decrease,” said Brown of the British Society for Immunology.
“In immunological terms, this finding is not unexpected, as we know that some other vaccines confer better immunity when the doses are more widely distributed. Although further information is needed to confirm these findings for older age groups, this new research should generally reassure ‘around the UK’s decision to offer the two doses of this vaccine 12 weeks apart.’
Similar data are not yet available on the postponement of the second dose of Pfizer / BioNTech vaccine until 12 weeks after the first dose, said Dr. Gillies O’Bryan-Tear, former chair of policy and communications at the Faculty of Pharmaceutical Medicine, told the SMC. But, he added, “most commenters agree that it will probably be the same with the vaccine, and indeed with other two doses of vaccinations.”
The authors warn that the trials were initially not designed to evaluate efficacy at dose intervals, but the data “arose from the logistics of conducting large-scale clinical trials in a pandemic environment.”
The primary analysis is based on 332 symptomatic infections that occurred more than two weeks after their second dose among more than 17,000 trial volunteers in the United Kingdom, Brazil and South Africa.
AstraZeneca announced last month that it is enrolling for its Phase 3 trial in the United States, which will serve as “the primary basis” for the company’s eventual application to the U.S. Food and Drug Administration.
The vaccine has already been approved in a number of countries, such as the UK and India, but according to Moncef Slaoui of Operation Warp Speed, the authorization will only come to the US in early March.