SAO PAULO | Residents of the Brazilian city of Manaus, heavily infected with the coronavirus, now benefit from a level of collective immunity to control viral circulation, according to a preliminary study published on Wednesday.
According to the mathematical model used by this study, published on the medRxiv site, 66% of the inhabitants of Manaus, where the pandemic has made a passage as fast as brutal, would have antibodies against the coronavirus.
This rate would be high enough so that the disease can no longer spread effectively, said the group of 34 Brazilian and international researchers, authors of this study which has not yet been the subject of a peer review.
Located in the Amazon rainforest, Manaus was the scene of images of overwhelmed hospitals, corpses piled into refrigerated trucks and mass graves when the epidemic was at its peak there in May.
Manaus has recorded 2,462 deaths from COVID-19. If it were a country, it would have the second highest death rate in the world, with 100.7 deaths per 100,000 population.
But the death toll in the city of 2.2 million people has dropped dramatically in recent weeks, to an average of 3.6 per day in the past 14 days.
“It appears that exposure to the virus itself has led to a drop in the number of new cases and deaths in Manaus,” said study coordinator, University of Sao Paulo medical professor Ester. Sabino, at the Sao Paulo State Research Support Foundation (FAPESP) which helped fund the study.
Manaus is one of the fastest declining cities in Brazil, for its schools, businesses, bars and its famous opera house.
However, for health experts, seeking to achieve herd immunity would be a dangerous path for policy makers.
“Collective immunity by natural infection is not a strategy, it is a sign that a government has failed to control an epidemic and that it is paying the price in lives lost”, tweeted Florian Krammer , professor of microbiology at the Icahn School of Medicine at Mount Sinai Hospital in New York.
Other experts have also warned that immunity could be short-lived after infection.
Brazil is the second most bereaved country in the world by the pandemic, behind the United States, with more than 138,000 dead.