On 14th August, I posted an interview from Professor Sunetra Gupta from the University of Oxford, who first expounded the theory that the UK has already reached herd immunity. Click for full post. A recent article in The Times this week provides a separate example of this hypothesis that herd immunity has been reached in a City of 2 million people in Brazil, where only 20% of the population of have been infected by covid-19. This exactly confirms Professor Gupta’s theory that populations have a degree of “natural” immunity, that She first propounded back in March.
An unexplained sharp fall in Covid-19 cases and deaths in the Brazilian city of Manaus has led experts to consider whether a form of herd immunity has been achieved in the Amazonian capital.
Manaus was once a symbol of the threat that the virus might pose to the developing world. Drone images of mass graves caused alarm around the world four months ago as Covid-19 ravaged the city and burials were running at five times their normal rate.
Yet last week, despite no formal lockdown having been imposed, and tests suggesting only 20 per cent of its population has been infected by the disease, “excess deaths” were listed at close to zero. The city’s field hospital has been closed for a lack of patients.
“Manaus is an interesting case indeed,” Jarbas Barbosa da Silva, assistant director of the Pan American Health Organisation, told The Washington Post. “The hypothesis — and this is just a hypothesis — is that the peak we had in Manaus was very strong, and there was such widespread community transmission that it may have produced some kind of collective immunity.”
Mr Barbosa said that the decline in cases was gradual enough to suggest “a natural dynamic” rather than the effect of public health initiatives. He insisted, however, that Manaus had “paid a very large price”. The city of two million people has recorded more than 3,300 deaths from Covid-19. “It was a tragedy,” he said.
The concept of herd immunity has proved highly contentious. In the early stages of the pandemic, the assumption among many leading epidemiologists was that more than 70 per cent of people would need to be infected for the disease to waste away naturally.
That policy was deemed unacceptable by almost all governments around the world as it was feared it would lead to hospitals being overwhelmed with tens of millions of deaths. More recent research suggests that herd immunity may be achieved with far fewer infections. One explanation could be that populations have a degree of “natural” immunity.
In Manaus, despite the high death toll when the disease first struck in the city, calls for the wearing of masks were largely ignored. Private schools reopened last month. Yet cases continued to fall. “There isn’t a concrete explanation,” Henrique dos Santos Pereira, a scientist at the Federal University of Amazonas, said. “The problem is that we don’t know how many people are susceptible.”