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Brazil has been hit hard by the pandemic, suffering more than 460,000 deaths. A shortage of jabs has resulted in a painfully slow vaccination campaign and the number of new infections and deaths remain high. The Instituto Butantan, which produces China's CoronaVac vaccine in Brazil, carried out an interesting experiment between February and April. This involved vaccinating practically the entire population of the town of Serrano in S茫o Paulo state which is surrounded by cities experiencing high rates of infection.

, 95 percent of Serrano's 45,000 inhabitants were fully vaccinated with CoronaVac during the above period. When that process was completed, symptomatic Covid-19 cases fell 80 percent, hospitalizations declined 86 percent and deaths plunged 95 percent. Ricardo Palacios, research director at Butantan, said that 75 percent was the crucial figure in the study. Once three quarters of Serrano's population was fully vaccinated, all three of the above metrics tumbled, suggesting 75 percent is the threshold required to contain and control the pandemic.