AstraZeneca Vaccine Appears to Reduce COVID-19 Transmission, Study Shows.br The analysis was conducted by researchers br at the University of Oxford in the U.K.br Though the study did not directly measure transmission, researchers collected regular nasal swabs from participants.br After one dose of the vaccine, the rate br of positive PCR tests fell by 67.br After two doses, the rate of positive br tests declined by about half.br A measure of overall PCR positivity is appropriate to assess whether there is a reduction in the burden of infection, Study authors, via CNN.br Most vaccine trials have only been able to observe br the prevention of symptomatic COVID-19 cases.br Dr. Doug Brown, chief executive of the br British Society for Immunology, .br says the study "hints that the OxfordAstraZeneca br vaccine may be effective in stopping people br being able to transmit the virus.".br While this would be extremely welcome news, we do need more data before this can be confirmed and so it's important that we all still continue to follow social distancing guidance after we have been vaccinated, Dr.