Has Manaus reached herd immunity? Well, it’s complicated

Back in April, Manaus — the biggest city in the Amazon basin — became Brazil’s textbook coronavirus worst-case scenario. With insufficient measures to control the outbreak, infection curves exploded — leading the city’s fragile healthcare network to a full-scale collapse. At one point, morgues were simply unable to handle the sheer amount of bodies showing up at their door, literally left to pile up. Cemeteries ran out of coffins and space, with corpses buried in mass graves known as “trenches.”

Months later, things seem to have improved significantly in Manaus. New daily deaths dropped from 56 during the pandemic’s peak to 3.9 as of September 29. The few social distancing rules in place were lifted, and in-person classes returned at schools around the state of Amazonas. 

The spread of the virus slowed down so significantly that a group of researchers, led by scientists from the University of São Paulo, went as far as suggesting that Manaus might have reached a so-called “herd immunity,” which would have made it the first place in the world to obtain this desired mark.

By analyzing blood samples, the study claimed to have found coronavirus antibodies in as much as 66 percent of the population. This would suggest that, as more people gain immunity, it would become harder for the virus to infect new people and continue its spread.

“Though nonpharmaceutical interventions — as well as a change in population behavior — may have helped to limit SARS-CoV-2 transmission in Manaus,...