observed in other COVID-19 vaccines, such as BNT162b1 and Convidecia. Variability in results In early January 2021, Brazilian health officials announced that the vaccine had an efficacy of 78%. One week later, they revised this figure to 50.4%, stating that the revised figure now included "very mild" cases of COVID-19 among trial participants which were omitted in the earlier analysis. Ricardo Palácios, medical director of Brazil's Instituto Butantan, said Sinovac's relatively low efficacy rate of 50% was due to more rigorous standards for what counted as an infection among trial participants. The Institute split cases in six categories: asymptomatic, very mild, mild, two levels of moderate, and severe; the first two didn't require medical assistance. Possible explanations for lower efficacy rate included: trial was largely made up of frontline health care workers who were more exposed to the virus; two vaccine doses were given at shorter intervals (2 weeks); counting very mild cases; and the Gamma variant (lineage P.1), more transmissible and perhaps evaded immunity better, was circulating. According to Instituto Butantan director Dimas Covas, the Brazilian group was considered more vulnerable to infection and exposure to higher viral loads. In Turkish and Indonesian Phase III trials, the composition of volunteers was similar to that of the general population. Variants On 10 March, Instituto Butantan Director Dimas Covas said CoronaVac was efficacious against three variants of COVID-19 in the country; Alpha (lineage B.1.1.7), Beta (lineage B.1.351), and lineage B.1.1.28 (identified in Brazil), from which Gamma and Zeta (lineages P.1 and P.2) descend. Preliminary results from a large study of health care workers suggest one dose of CoronaVac is still about 50% effective against symptomatic COVID-19 in Manaus. In April 2021, it was reported that over 75% of new cases were being caused by the highly transmissible Gamma variant. In June, Thailand's Public Health Ministry stated the vaccine had 71%-91% efficacy against infection by the Alpha strain. In June 2021, Reuters reported that more than 350 Indonesian doctors and medical workers out of 5,000 in Kudus contracted the Delta strain despite being vaccinated with the CoronaVac, an infection rate of 7%. In response, Griffith University epidemiologist Dicky Budiman questioned the efficacy of CoronaVac against the variant but overall still recommended that people take the vaccine, expressing "confidence that to a certain degree Sinovac has effectiveness against the new variant". He stated that the situation was due to various factors, including a