An unexpectedly positive turn for Brazilian cities once plagued by the coronavirus pandemic raises fresh questions about immunity.
A new report in the Washington Post described how the impoverished city of Manaus saw hospitalizations decline, although it had never imposed a lockdown or taken other drastic austerity measures in Asia and Europe. It also tests far more residents than ever before.
Initially, medical experts believed that between 60 percent and 70 percent of the population needed antibodies to achieve collective immunity, but Manaus never passed 20 percent. And the Amazon city of 2 million suffered three times as many deaths in the spring as normal.
There are too many unknown variables to be sure, however, in the broader debate about virus transmission and the level that needs to be crossed before the number of infections begins to tap into it – especially in large cities like the Amazon capital.
Many researchers believe that collective immunity works differently in a live outbreak like coronavirus than in something like the mice. The virus does not disappear at a specific point, but the transmission slows down until it is eradicated.
They report that, although strict restrictions are effective, once the virus infects a critical mass, a resurgence in cases is unlikely.
While the concept of herd immunity has long been used to explain the purpose of mass vaccination campaigns, the answer now seems to be more complex.
Scientists have studied the possibility that individual variants in vulnerability reduce the ratio of infection by which herd immunity can be achieved. Some, research data from European cities, theorize that immunity could be achieved with rates lower than 20 percent.
Many other cities around the world that were once devastated by coronavirus have begun to open up without second waves, with some speculating that collective immunity has been achieved.
Harvard epidemiologists have hypothesized that parts of London and New York have already reached “substantial immunity”. The same is said by health officials in very close areas like India’s Mumbai, although the first recorded COVID-19 reinfection was just confirmed in Hong Kong.
Swedish health experts claimed that they had also achieved herd immunity, while refraining from recommended procedures such as wearing masks and hard shots.
Residents of Manaus meanwhile hope infections remain at bay.
Mayor Arthur Virgílio Neto – who had the virus himself – has indicated that if a second wave hits, the city’s capabilities would be “overwhelmed” again.
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