Instituto Butantan

Immunization of Serrana´s population with Butantan´s vaccine has a high decrease of 80% cases and 95% in deaths by COVID-19

Publicado em 31 maio 2021

The Coronavac, applied in 27,1 thousand residents of the municipality, localized in the region of Ribeirão Preto protected vaccinated and non vaccinated, creating a collective “immunological belt” against the virus, reducing drastically its transmission, as revealed by the unprecedented study in the world. 

The immunization of all the adult population of the municipality of Serrana, in the countryside of São Paulo, with the Butantan´s CoronaVac caused a great reduction of 80% of the symptomatic cases and 95% of deaths after the second vaccination of the last group of the city (please see the trust gap in the end of the text). 

This is the main conclusion of the clinical study of effectiveness - named “Project S” - an unprecedented study in the world, coordinated by the Institute that is related to the Government of São Paulo. 

The reduction was stated by the comparison of the data from the beginning of the project until the vaccination of all the groups was completed - with all the trimester evaluated (february, march and april of 2021). 

The results also showed that the vaccination protects not only the adults that received the two doses of the immunization but also the children and teenagers with less than 18 years old who were not vaccinated. 

This proves that the intervention made in the city by Butantan created in it a true “immunological belt” with a collective barrier against the virus, drastically reducing the transmission in the municipality. 

Another important conclusion of the research is the incidence of the disease in Serrana in comparison with the nearby cities. Serrana has around 10 thousand residents that works  in Ribeirão Preto daily. However, while Ribeirão Preto and others cities in the region are presenting high levels of COVID-19 cases, Serrana maintained low taxes if compared to the cities with similar profile, due to the vaccination. 

In other words, the success of the vaccination was confirmed not only by the decrease in the number of infected people but also showed that the residents of Serrana that goes daily from one city to another did not bring a relevant increase in the number of cases. 

Between February 17 and April of this year, during 8 weeks, around 27 thousand residents of the municipality received the completed vaccination scheme: two doses of the Coronavac with a gap of 28 days between the first and second doses. This represents a coverage of approximately 95% of the adult population of residents, according to the health census made previously by Butantan. 

The research, conducted by Butantan Institute and approved by the ethical and sanitary authorities, counted with the partnership of the Medical School of USP in Ribeirão Preto and with the Municipal Government of Serrana. 

The method used for the clinical trial is called stepped-wedge trial. The city was split in 25 sub areas forming four populacional groups, named clusters and identified by colors - green, yellow, gray and blue - which received the immunizing following this order. The vaccine was offered to all residents aged over 18 years eligible to the study in these areas, sequentially and in four degrees. 

The study also concluded that the two last populacional groups participating on the vaccination were already benefiting from the reduction of the transmission of the virus generated by the immunization of the residents of the two first groups. 

The medical director of the clinical research of Butantan Institute, Ricardo Palacios, who also directed the study, explains that the sequential scheduling permits the evaluation of the four vaccinated areas. 

“We understood that the phenomena observed did not happen randomly, but it repeats in the four groups in different moments' ' explains. “The most important result was understanding that we can control the pandemics even without vaccinating all the population. When reaching the coverture of 70 to 75%, the degree in the incidence was detected even in the group that had not completed the vaccination scheme already” completes. 

According to Palacios, the clinical trial also confirmed the indirect effect of the vaccination, since it was possible to prove the protection of populations that were not vaccinated, such as the children. “ The reduction of the cases in people who did not receive the vaccine indicates the degree of the virus circulation. This enforces vaccination as a public health measure and not only an individual action” says the director of the study. 

The municipality of Serrana was chosen to host the project and presents, by the time, a high level of prevalent infections by COVID-19 and by the fact that it has a regional hospital. The goal was to study the epidemiological impact of the vaccination on the adult population group, regarding the contention of the pandemic. 

The vaccine was applied upon the volunteering participation of the residents. People attended to receive the immunizing in previously scheduled dates. 

“The important conclusions of this study can support the strategies of immunization not only in Brazil but throughout the world, and it offers hope in the control of the pandemic with vaccines as the Coronavac, which was developed in partnership of the chinese pharmaceutical Sinovac with Butantan” states the president of the Institute, Dimas Covas. 

According to the scientist and professor, the study of phase 4 proves the efficiency of the vaccine as a collective health strategy. The clinical trials of the phase 3, made between july and december of 2020, had already assured the efficacy of the immunizing, with varying levels between 50,7% to 62,3% to symptomatic cases and from 83,7% to 100% in occurences that demands any medical assistance. 

“The vaccine is secure, effective, efficient, has a high level of quality and contributes to prevent the development of the disease, complications and deaths between the infected. We also know now that it causes beneficial effects in a whole population, protecting the vaccinated, the non vaccinated and significantly reducing the virus circulation.” concludes the president of Butantan. 

Trust Gaps in the reduction levels mentioned in the first paragraph

Symptomatic cases 

- Decrease of 80%  (IC95 76,9% - 82,7%) 


- Decrease of (IC95 74,1% - 92,3%)


- Decrease of (IC95 62,7% - 99,3%)

Get to know more about Project S

Access the website (

Follow on Instagram (@projetoserrana)

Listen to the podcast on Spotify

Watch the documentary on Youtube

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