Mass Vaccination Success in This Small Brazil City Shows Promise of Low-Efficacy Vaccines

In Serrana, 95 percent of adults received the CoronaVac vaccine, which has a 50% efficacy rate. Now, the city is ready to reopen

On February 17, 2021, residents line up to receive the Coronavac vaccine against COVID-19, in Serrana, about 323 km from Sao Paulo, Brazil.
Part of a clinical study called Project S, a small town in Brazil set out to vaccinate its entire adult population. With 95% of adults vaccinated, the city has seen a steep decline in Covid-19 cases, hospitalizations and deaths. Photo by NELSON ALMEIDA/AFP via Getty Images

Between February and April this year, about 95 percent of adults in Serrana, a small city in Brazil, received two doses of the CoronaVac Covid-19 vaccine. Now, Serrana is reopening as other cities in the region are seeing a rise in Covid-19 cases, Mauricio Savarese reports for the Associated Press.

The vaccination program allowed researchers to track the real-world effects of mass vaccinations. The preliminary results of the vaccination program showed an 80 percent drop in symptomatic Covid-19 cases, an 86 percent drop in hospitalizations and a 95 percent drop in deaths caused by Covid-19, Sofia Moutinho reports for Science magazine. The initial findings, which have not been peer-reviewed, were announced in a press conference on May 31.

The researchers found the local outbreak of Covid-19 was brought under control after just 75 percent of adults in Serrana received the CoronaVac vaccine.

“The most important result was understanding that we can control the pandemic even without vaccinating the entire population,” says Ricardo Palacios, a director at the Butantan Institute in Sao Paulo and a coordinator of the study, to the Associated Press.

The CoronaVac vaccine uses an inactivated form of the pandemic coronavirus to teach the immune system how to fight off a live infection. The vaccine, produced by a Chinese company, was just approved for emergency use by the World Health Organization, Smriti Mallapaty reports for Nature. The CoronaVac vaccine has an efficacy rate of just over 50 percent, which raised concerns about whether it could make a significant impact.

“This project is important because it shows that even a vaccine with relatively low efficacy can have high efficiency and significantly decrease death rates in real-life settings,” says Mellanie Fontes-Dutra, the coordinator of Brazil’s Covid-19 Analysis Network and who was not involved in the study, to Meghie Rodrigues at Science News.

Serrana was chosen for the vaccination program because of its moderate size of about 45,000 residents. The town also had a high rate of Covid-19: one in 20 residents were infected with the virus, and about a quarter of residents had been exposed to it. The program was called “Project S” because it was kept secret to avoid people migrating to the town for access to the vaccine, reports Science magazine.

A team of 15 researchers organized the city’s residents into four groups. Each group was received a dose of the vaccine one week apart and received a second dose four weeks after the first. The vaccine was offered to all adults 18 years old and older who did not have chronic health conditions and who were not pregnant. After eight weeks, about 27,000 people were vaccinated through the program.

Now Serrana is reopening churches and planning a music festival, per the Associated Press. Elsewhere in Brazil, vaccine rollout is still focused on elderly people and those at highest risk of severe disease, per Science.

Experts tell Science magazine that more data, gathered over a longer period of time, is needed to confidently determine the effectiveness of the vaccine. “Project S” will continue to monitor Serrana for a year to measure the effectiveness of the CoronaVac vaccine, and to determine whether recipients of the vaccine will need booster shots. The researchers also plan to submit their results to a peer-reviewed journal and may publish a pre-print before then.

“But these preliminary numbers show we have an effective vaccine,” says Fontes-Dutra to Science News. “And the most important thing to do is expand vaccination coverage as much as we can to have as many immunized people as possible.”