Residents of the Brazilian city of Manaus, heavily infected with the coronavirus, would now benefit from a level of collective immunity to control viral circulation, according to a preliminary study published Wednesday on the medRxiv site.
Some 66% of residents have antibodies against the coronavirus, a rate high enough that the disease can no longer spread effectively, said the group of 34 Brazilian and international researchers, authors of the study.
Their research, however, has not yet been peer reviewed.
Dramatic drop in the number of deaths
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 there was at its peak 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 fourteen 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 São Paulo medical professor Ester Sabino, at the São Paulo State Research Support Foundation (FAPESP) which helped fund the study.
"Collective immunity by natural infection is not a strategy"
Manaus is one of the fastest declining cities in Brazil.
But 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.
Since I already see it going this way: I did not endorse community immunity as a strategy.
Community immunity via natural infection is not a strategy, its a sign that a government failed to control an outbreak and is paying for that in lives lost.
- Florian Krammer (@florian_krammer) September 22, 2020
Other experts have also warned that immunity may 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 deaths.
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