Brazilian town experiment shows mass vaccination can wipe out COVID-19



A small commuter town surrounded by sugarcane fields in southeastern Brazil, one of the countries hardest hit by COVID-19, has shown that even a vaccine that had low efficacy in some clinical trials can dramatically control the pandemic virus.

As part of an unusual experiment to track the real-world effectiveness of CoronaVac, a COVID-19 vaccine made by a Chinese company, almost all adult residents of Serrana, in the state of São Paulo, received the required two shots between February and April, long before most would otherwise have become eligible for the vaccine. The results were dramatic. Symptomatic cases of COVID-19 have dropped by 80% since the start of mass vaccination, related hospitalizations fell 86%, and deaths plummeted 95%, the research team in charge of the experiment reported during a press conference yesterday.

Meanwhile, cases have risen out of control in 15 other cities nearby. “Serrana is now an oasis,” says Ricardo Palacios, an epidemiologist at the Butantan Institute, a state-owned research center that produces the vaccine in Brazil. “And it has shown us that it is surely possible to control the epidemic through vaccination.”

Some other COVID-19 vaccines have demonstrated greater than 90% real-world effectiveness at preventing serious disease, and they have helped countries bring cases down to very low levels. But there has been concern about CoronaVac, which uses an inactivated copy of SARS-CoV-2 to stimulate immunity. Clinical trials conducted in several countries came up with different efficacy values for the vaccine, the lowest being 50% in Brazil—right at the threshold established by the World Health Organization (WHO) for emergency use of a COVID-19 vaccine. Later studies in Brazil that tried to assess the vaccine’s real-world effectiveness have indicated similar levels of protection.



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