The rate of positive CRP tests decreased by about half after two doses, according to preliminary results from Oxford University researchers who have not yet been evaluated by peers.
The study did not measure transmission directly – for example, by tracking contacts that were infected by study volunteers. But the researchers collected 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 just one dose, the rate of positive tests dropped 67%.
“Although the transmission studies themselves were not included in the analysis, swabs were obtained from volunteers every week in the UK study, regardless of symptoms, to allow an assessment of the overall impact of the vaccine on the risk of infection and therefore , a substitute for potential future transmission “, write the authors.
If the vaccine were simply making infections milder, PCR positivity would not change, the authors argued in the prepress analysis. “A measure of the overall positivity of CRP is appropriate to assess whether there is a reduction in the burden of infection.”
Coronavirus vaccine trials have primarily looked at the prevention of symptomatic cases of Covid-19. Previously, there were few other public data suggesting that vaccines could prevent people from passing the infection on to others.
Speaking to the UK’s Science Media Center (SMC), Helen Fletcher, professor of immunology at the London School of Hygiene and Tropical Medicine, said the study’s data “suggests a possibility that the vaccine could have an impact on transmission, but further on – it would be necessary to confirm this. “
Dr Doug Brown, chief executive of the British Society for Immunology, told the SMC that the study “suggests that the Oxford / AstraZeneca vaccine may be effective in preventing people from transmitting the virus”.
He added: “While this is extremely welcome news, we need more data before it can be confirmed and it is therefore important that we all continue to follow the social detachment orientation after we have been vaccinated.”
Dose spacing
The vaccine showed 66.7% effectiveness against symptomatic diseases starting two weeks after the second injection, researchers at Oxford University said.
The new analysis adds new test sites and a month of new data to the mix, based on previous results announced by AstraZeneca that its vaccine had shown an estimated 70.4% effectiveness.
However, the latest research also suggests that the vaccine may offer substantial protection after a single injection.
The study estimates 76% effectiveness up to three months after a dose. This is based on a subset of 88 symptomatic infections, divided unevenly 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 minimal decrease on day 90”.
In addition, the authors suggest that there may be greater efficacy with more widely spaced doses. Among adults 18 to 55, the vaccine’s effectiveness appeared to increase when the time between vaccines was spaced from less than six weeks to more than 12. However, more information is needed to know how statistically different this finding is.
Together, the findings may support the UK’s decision to recommend doses spaced up to 12 weeks apart, according to a statement by the Oxford Vaccine Trial lead investigator and co-author of the article, Andrew Pollard.
“This is positive news, as it shows that just one dose of this vaccine generates good levels of immunity and that this protection does not appear to decrease 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 doses are more widely distributed. Although more information is needed to confirm these findings for older age groups, in general, this new research should provide assurances around the UK’s decision to offer two doses of this vaccine 12 weeks apart. “
Similar data are not yet available on the postponement of the second dose of the Pfizer / BioNTech vaccine for 12 weeks after the first dose, said Dr. Gillies O’Bryan-Tear, former president of policy and communications for the Faculty of Pharmaceutical Medicine in comments to SMC. But, he added, “most commentators agree that it is likely to be the same with that vaccine, and indeed, other two-dose vaccines.”
The authors caution that the trials were not initially designed to assess effectiveness at dose intervals, but the data “emerged due to the logistics of conducting large-scale clinical trials in a pandemic scenario”.
The primary analysis is based on 332 symptomatic infections that occurred among more than 17,000 study volunteers in the United Kingdom, Brazil and South Africa, more than two weeks after the second dose.
AstraZeneca announced last month that it has completed enrollment for its Phase 3 test in the United States, which will serve as “the main foundation” for the company’s eventual application to the US Food and Drug Administration.
The vaccine has already been authorized in several countries, such as the United Kingdom and India, but the authorization may not reach the United States before the end of March, according to Operation Warp Speed’s Moncef Slaoui.