DUBLIN — Almost one-third of Americans could have been infected by the coronavirus in 2020, according to Columbia University estimates.
Published in the journal Nature, the research by the Ivy League university’s Mailman School of Public Health suggests 103 million people, or 31 per cent of the population, caught the virus last year, far more than the official year-end tally of just over 20 million, of which 351,998 had died by December 31.
“The vast majority of infectious were not accounted for by the number of confirmed cases,” said Jeffrey Shaman, professor of environmental health sciences at Columbia.
Official numbers were accounting for only 10 per cent total estimated infections at the outset of the pandemic in March, when testing was not widely accessible, but rose to 25 per cent by December, according to the researchers.
At first, “individuals with mild or asymptomatic infections, who could still spread the virus, were less likely to be tested,” they said.
Testing and treatments improved over time, meaning “the percentage of people with infections who died from Covid-19 fell from 0.8 per cent during the spring wave to 0.3 per cent by year’s end,” when official counts were likely capturing around a quarter of real infections.
The National Academy of Sciences last month published estimates by the University of Washington suggesting around one-fifth of Americans had caught the virus by March this year, before the spread of the “Delta” variant, which the Harvard’s Mailman School last week estimated to be 60 per cent more infectious than the early strains.
The World Health Organization (WHO) last year estimated that 10 per cent of the world’s population, or around 700 million people, could have already been infected by the virus by September 2020.
Almost one year on, the official global case count on August 25 was around 200 million worldwide, of which around 38 million had been reported in the US.
An undercount of infections would mean the virus is less deadly than confirmed numbers suggest, widening the infection-fatality rate substantially beyond the official case-fatality rate, and meaning far more people could have naturally-derived immunity to the virus than is officially acknowledged.
Over 630,000 people have died in America after testing positive for the virus. The cumulative case-fatality rate for the US was 1.6 per cent on August 25, based on official death numbers collated by the University of Oxford’s Our World in Data.Show