Thread by @hildabast

Preprint on Brazilian trial by @butantanoficial of Sinovac's CoronaVac, 2 weeks apart. Data for 9,823 people who had 2 doses, 12,396 after 1 dose.The P1 ("Brazilian") variant of concern was not circulating in the areas the trial ran...1/n papers.ssrn.com/sol3/papers.cf… HT @josegallucci

...14-day interval seems too close, & immunity may increase over time: they recommend 28 days. Their primary efficacy, unlike other vax trials, includes people who had previous SARS-CoV-2 infection. But this table provides the comparable number: 50.5% (CI 34-63)..2/n

...Their primary efficacy analysis was based on 85 vs 168 people with symptomatic Covid-19. Unfortunately, they don't provide detailed data on symptoms so can't try to see whether this was milder disease than other trials... 3/n

...Primary efficacy after 2 doses
- Any Covid-19: 50.7% (CI 36-62)
- Covid-19 requiring medical care: 83.7% (CI 58-94)
- Moderate/severe Covid-19: 0 vs 6, 100% (CI 56-100)
- With interval of 21 days or more, 62.3% (CI 14-84) (high degree of uncertainty, not many people)...4/n

...Efficacy was similar for the 5% of the group that were aged 60 or older. Efficacy 14 days after the 1st dose was 57·9% (CI 46-67)...5/n

...Very low rate of adverse events other than injection pain. No serious event judged related to vax. Rate of severe (grade 3) wasn't higher in the vaccinated group, systemic events were similar...6/n

...They took samples for 109 people before vax & 2 weeks after 2nd dose, 6 of whom showed signs of previous infection. For the other 103, 45 became infected. The rate of people testing positive for P1 was high, if I'm understanding correctly...7/n

...All up, very low rate of adverse events & good protection against severe disease. Not a very big trial, so fair amount of uncertainty. Efficacy seems reduced by variants & too short an interval between doses, but not enough data to be sure. /8

...PS: @butantanoficial's other critical trial of CoronaVac is the whole-of-town stepped-wedge trial in Serrana. 2nd dose completed on Sunday 👏 - but we don't know yet what the final percent. (Meanwhile though, severe disease has been dropping there 🤞🤞 while surges in Brazil)

...Correction to tweet 7: @Hepta7bi2 points out this is likely testing for ability to neutralize variants, not being infected with them, which makes more sense.