.@ShabirMadh, principal investigator of the SA arm of the #astrazenecavaccine: This slide explains who participated in the SA arm of the study: Adults between 18 and 65, everyone got 2 doses, 2000 participants. To show protection we need 60% protection, Madhi says. 
The Oxford/AstraZeneca study wasn't designed to determine whether the vaccine protects against severe #COVID19 disease or not. Rather, it looked at mild to moderate disease.
Those who develop severe disease are the ones who will end up in hospital or die - it's important that vaccines protect against severe disease. But our study only looked at if the vaccine protects against mild and moderate #COVID19 disease.
The enrolment started when the first wave was peaking. But then there was a rapid decline in infections. So by the end of the wave only a quarter of participants had received their vaccines.
A new variant #501YV2, also known as #B1351 emerged late last year. How well the #AstraZeneca worked until end of October, before the new variant became dominant.
Until the end of October 2020 (before the variant emerged), the protection conferred by the #AstraZeneca vaccine provided similar levels of protection in the UK, SA and Brazil.
In SA, where 25%-30% were infected during the first wave, there was a lot of immune pressure built up against the virus, and the virus therefore had to evolve and change to better survive.
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