Coronavirus: Herd immunity

90% of Americans still susceptible to Covid-19: Experts

Data shows herd immunity is still very far off, countering belief that pandemic is all but over

Commuters in the New York borough of Brooklyn, where cases are on the rise again. The experts' findings run counter to a theory promoted by some that the US has achieved herd immunity or is close to doing so. PHOTO: AGENCE FRANCE-PRESSE
Commuters in the New York borough of Brooklyn, where cases are on the rise again. The experts' findings run counter to a theory promoted by some that the US has achieved herd immunity or is close to doing so. PHOTO: AGENCE FRANCE-PRESSE

WASHINGTON • In the last week, leading epidemiologists from respected institutions have, through different methods, reached the same conclusion: About 85 per cent to 90 per cent of the American population is still susceptible to Sars-CoV-2, the virus causing the current pandemic.

The number is important because it means that "herd immunity" - the point at which a disease stops spreading because nearly everyone in a population has contracted it - is still very far off.

The evidence came from antibody testing and from epidemiological modelling.

At the request of The New York Times, three epidemiological teams last week calculated the percentage of the country that is infected.

What they found runs strongly counter to a theory being promoted in influential circles that the United States has either already achieved herd immunity or is close to doing so, and that the pandemic is all but over.

That conclusion would imply that businesses, schools and restaurants could safely reopen, and that masks and other social distancing measures could be abandoned.

"The idea that herd immunity will happen at 10 per cent or 20 per cent is just nonsense," said Dr Christopher Murray, director of the University of Washington's Institute for Health Metrics and Evaluation, which produced the epidemic model frequently cited during White House news briefings as the epidemic hit hard in the spring.

That belief began circulating months ago on conservative news programmes like those of Mr Rush Limbaugh and Ms Laura Ingraham.

It has been cited several times by Dr Scott Atlas, US President Donald Trump's new pandemic adviser. It appears to be behind Mr Trump's recent remarks that the pandemic is "rounding the corner" and "would go away even without the vaccine".

Its most vocal adherents are calling for mask wearing and social distancing to end just as cold weather is shifting social activity indoors, where the risk of transmission is higher.

Even in places where the pandemic hit especially hard - a French aircraft carrier, the Brazilian city of Manaus, the slums of Mumbai in India and a neighbourhood in Queens, New York - infections did not noticeably slow down until almost 60 per cent of the inhabitants were infected.

And even those levels may not suffice, given that cases are increasing again in Brazil and in areas in the New York borough of Brooklyn that had seen cases spike and then drop off.

The chief proponents of the idea that herd immunity is somehow close at hand contend that most people in the world are immune to the virus, thanks to "T cell immunity" derived from having contracted common colds that were caused by the four relatively benign coronaviruses that have circulated for years.

But this theory is unfounded.

Dr Thomas Frieden, a former director of the Centres for Disease Control and Prevention, said: "Immunity in 2020 is no closer to being just around the corner than prosperity was in 1930."

More than 200,000 Americans have already died, and models estimate that if people return to old habits, more than 300,000 and possibly 400,000 could die before a vaccine is widely available.

NYTIMES

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A version of this article appeared in the print edition of The Straits Times on October 01, 2020, with the headline 90% of Americans still susceptible to Covid-19: Experts. Subscribe