Brazil's experiment with the Chinese CoronaVac: secretly vaccinating an entire city

Brazil's experiment with the Chinese CoronaVac

Clinical studies have found that Sinovac's Chinese CoronaVac vaccine is not effective in preventing symptomatic cases of Covid-19. But research on mass vaccination in the city of Serrana in Brazil instead shows very favorable data

(photo: MIGUEL SCHINCARIOL / AFP via Getty Images) The CoronaVac vaccine from Chinese pharmaceutical Sinovac also proved very useful in a clinical study conducted in Brazil, in the city of Serrana. In some clinical studies, Sinovac's vaccine appears to have a rather limited efficacy equal to 51% in preventing symptomatic cases of Covid-19, and up to 100% in avoiding hospitalizations and deaths.

But an experiment conducted today in Brazil shows somewhat different preliminary data. The experiment, called Project-S, concerns the mass vaccination of the entire population of the city of Serrana, in the State of Sao Paulo, with Sinovac's CoronaVac vaccine. The survey highlights that in the period immediately following the administration of the second dose, the vaccine was able to reduce symptomatic cases by 80%, hospitalizations by 86% and deaths by 95%. The data, limited to the city of Serrana, seem to rehabilitate this vaccine (at least in a specific situation) which has so far been little considered. The results, to be confirmed and not yet published, were presented at a press conference of the government of the state of São Paulo. CoronaVac, currently being evaluated by the EMA, has just been approved by the World Health Organization, which indicates that the vaccine complies with safety, efficacy and production standards.

Project-S, the experiment and mass vaccination

In Brazil the vaccination campaign is still proceeding quite slowly and according to the data the adults who have received at least one dose are about 22% (in Italy we are about 39% as of June 3). The study involved the 45 thousand inhabitants of the city of Serrana, a municipality in the State of Sao Paulo. The project, in which the Butantan institute took part, is called Project-S, where the S does not stand for Serrana but for secret, since at the beginning the news of the ongoing investigation was kept confidential so as not to recall in the small city ​​non-resident groups. The goal was to vaccinate all eligible individuals with CoronaVac, a vaccine which is also widespread in Brazil and used in 80% of cases. It is a real experiment to observe what results would have been obtained with the mass vaccination of a population.

All people over 18 years of age, without chronic diseases and not pregnant, have received the CoronaVac vaccine, for a total of about 27 thousand residents who received two doses, about 95% of the population.

CoronaVac, how Project-S took place

At the time of departure of the study one in 20 inhabitants were positive for coronavirus and 2 5% of the local population had already been exposed to Covid-19. From February to April 2021, scientists administered the two doses in a mass vaccination campaign within the municipality. The researchers divided the city into 4 areas of risk of contagion, a division not only geographic but also of population that identifies microcosms of people most in contact. When 3 of the 4 population groups corresponding to the 4 identified areas had received the vaccination, the epidemic in the city was finally under control. The decrease in symptomatic cases was significant and much higher than 51%. This percentage, estimated in some clinical trials, represents the effectiveness of the CoronaVac vaccine in preventing Covid-19 symptoms in the vaccinated population, while from the evidence already collected the effectiveness against severe forms and hospitalizations would be much higher, up to 100% .

How to interpret the data, not yet published

The data are not yet reported in a publication and therefore it is advisable to wait and keep all precautions before interpreting them in any way. Researcher Ricardo Gazzinelli, president of the Brazilian Society of Immunology, points out that two months of observation (March and April) are few to draw conclusions and that research and monitoring will continue. At first glance, the result might strike attention, considering the previous estimate of effectiveness of 51%. However, the real life and circumstances of each country or city are very different and can also change the outcome of the vaccination campaign, as this study shows. The hypothesis, clearly explained in an article in Science, is that mass vaccination combined with the previous exposure to the virus of a good portion of the local population may have favored the achievement of the coveted herd immunity.


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