Ross Clark Ross Clark

Has this Brazilian city reached herd immunity without lockdown?

A nurse performs a coronavirus test on a resident near Manaus, Picture: Getty

Throughout the Covid crisis, the international response to the disease has rested on a simple assumption: that none of us have any resistance to it, being caused by a novel virus. Therefore, if allowed to let rip through the population, the virus would exponentially spread until around 60 – 70 per cent of us had been infected and herd immunity was reached. This was the assumption behind Neil Ferguson’s paper in March, claiming that Covid-19 would kill 500,000 Britons if nothing was done and 250,000 of us if the government carried on with the limited mitigation polices it was then following.

Yet real world data has challenged this assumption. First came the accidental human experiment of the Diamond Princess cruise ship, where in January the disease spread unnoticed among 3,711 passengers and crew in the closed environment of a ship. But when all those people were tested for the disease, only 19 per cent turned out to have been infected. Similarly, as reported in the Spectator in March, a study of 1,286 people in the southern Chinese city of Shenzen revealed that only 14.9 per cent of people who shared an apartment with someone later found to be suffering from Covid-19, had picked up the infection themselves.

Perhaps it is time the government starts looking at real world evidence, rather than just models

In New York City, a runaway epidemic seems to have left after antibody tests on a sample of the population revealed 21 per cent of the population had been infected. In London, the epidemic appears to have retreated after 17 per cent were infected.

There is now another piece of powerful evidence suggesting that the assumption we are all susceptible to Covid-19 could be wrong. The Amazonian city of Manaus has witnessed a remarkable retreat in what had seemingly been an uncontrolled epidemic among its 2 million population.

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