COVID-19: Vaccination Experiment in a Brazilian Town Reveals Surprising Results

Brazil is among the hardest hit countries by COVID-19, with over four lakh deaths. In order to control the pandemic, an unusual experiment with vaccination was conducted in a small town, named Serrana, situated in the southeastern part of the country. The experiment showed that even a vaccine showing low efficacy in some prior clinical trials can have a dramatic effect in controlling the COVID-19 virus.

As part of the experiment, the vaccine known as CoronaVac, made by a Chinese company, was administered to almost all adult residents of Serrana. All of them received the two doses of the vaccine between February and April, long before most of those vaccinated would have become eligible for vaccination.

The results of the unusual vaccination experiment were surprising. The research team in charge of conducting the experiment declared in a press conference recently that symptomatic COVID-19 cases have dropped by 80% since the mass vaccination started, hospitalisation dropped by 86% and deaths fell by 95%.

However, the rest of the country is nowhere near controlling the spread of the disease, 15 other cities nearby Serrana reported to have new cases rising out of control. Ricardo Palacios, an epidemiologist associated with Butantan Institute, the state owned research institute that produced the vaccine in Brazil said in a statement, “Serrana is now an oasis, and it has shown us that it is surely possible to control the epidemic through vaccination.”

There were concerns over the success of CoronaVac as it showed varied efficacy values in different countries. Notably, the clinical trials conducted in Brazil showed the lowest efficacy level of 50%. This efficacy level is the threshold set up by the World Health Organisation (WHO) to be considered for emergency use as a COVID-19 vaccine.

The results are encouraging for the scientists in Brazil for two reasons. First, despite the low efficacy level, the CoronaVac vaccine makes up almost 80% of all the vaccine doses administered. Secondly, the mutant variant known as the P1 variant, which originally emerged in Brazil itself is the most prevalent one in Serrana and also in the country. Some previous studies had suggested that the P1 variant can evade protection from vaccine.

On June 1, WHO granted CoronaVac, made by the Chinese company Sinovac, for emergency use listing. This is indeed a welcome step as it would speed up the use of the vaccine in many low-income countries. 

The mass vaccination programme in Serrana was named as ‘Project S’, where S stands for secret. The plan was initially not highlighted as Brazilian authorities feared a mass migration to Serrana. The team which conducted the experiment comprised of 15 researchers and they were supported by local authorities and health workers.

The team divided Serrana into 25 sections and each of it represented a small sample of people who interacted with each other, for example, people living in same residential complex or shop in the same stores. The researchers then chose four groups of residents from among the clusters and vaccinated each group one week apart. So, each group would receive the second dose after four weeks of getting the first one. The vaccines were available for those above 18 years of age. Proceeding in this fashion, after eight weeks, 96% of the eligible residents received two doses of the vaccine and the vaccination showed no severe side effects. The town has a population of about 45,000.

During the process of vaccination, Serrana was never closed or isolated from its neighbouring cities.

While, the results of the study have not yet been published in a peer reviewed journal, the researchers involved in it have said that it will soon be published.