The mass experiment where nearly every adult in a single town was vaccinated against Covid

As countries around the world battle against coronavirus, one town in Brazil has shown how important the vaccine is to fight it.

Serrana, a city in the southeastern Brazilian state of Sao Paulo, became the subject of a study that saw almost all its adult population vaccinated.

Between 17 February and April, around 27,000 Serrana residents – approximately 95% of the adult population – received two doses of the Sinovac vaccine.

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The city has since seen a 95% drop in Covid-19 deaths and an 80% drop in cases, according to the Instituto Butantan, which ran the study.

The institute, which produces the Coronavac vaccine developed by China's Sinovac Biotech in Brazil, said the experiment has created a collective “immunological belt” against coronavirus in Serrana.

China has also sent the Sinovac vaccine to be used in many developing countries.

It comes while the rest of Brazil, which has the world's second-deadliest outbreak with more than 461,000 deaths so far, has had a very slow immunisation pace due to the lack of vaccines.

The study leaders say the results show the vaccination protects not only the adults that received the two doses of the immunisation, but also the children and teenagers under 18 who were not vaccinated.

The scientists also found cases remained low in Serrana despite thousands of its residents travelling to work in neighbouring cities where Covid cases are still high.

Serrana initially saw an increase in Covid cases when vaccinations began in February.

But the spread of the virus was contained once 75% of the population was immunised, scientists found.

They divided the city into four areas and found that the virus was controlled after three had received the second dose.

Study leader Ricardo Palacios, medical director of clinical research at Butantan Institute, said: “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.”

He added: “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.”

The researchers said Serrana was chosen for the experiment due to the high level of prevalent infections by Covid-19 and because it has a regional hospital.

Researcher Dimas Covas said: “The important conclusions of this study can support the strategies of immunisation 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.”

A similar experiment is underway in Botucatu, another city in Sao Paulo, which expects to immunise most of its 148,000 inhabitants with the AstraZeneca vaccine.