It seems that the different vaccines trials did not test all those during the trials for covid-19 and so may have over estimated some vaccines effectiveness - how much does this effect the differences between the Astra-Z trials and other vaccines
The researchers at the University of Oxford
conducted weekly coronavirus tests of participants in the U.K. enrolled in a vaccine trial and found that the rate of positive results declined by about 67% after participants received one dose.
Other vaccine studies, by contrast, have
mainly tested people who showed symptoms of COVID-19, not everyone enrolled in the trial, which means they couldn't tell how many vaccinated people were asymptomatic, but still infectious to others.
Testing negative means no virus is present and makes it less likely a person is infected, even asymptomatically. People without detectable virus in their respiratory tract can't spread the virus. The work has not yet been peer-reviewed but was published as a preprint with the Journal The Lancet.
You have likely heard that Pfizer's COVID-19 vaccine efficacy is 95%, Moderna's is 94% and Johnson & Johnson's is 66%. But what do these numbers actually mean? COVID-19 vaccines: What does 95% efficacy actually mean? : Read more
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