Around one third of Americans had been infected with Covid-19 by the end of 2020, according to new research published in the journal Nature Thursday, suggesting a much wider spread of the coronavirus than what official testing detected and highlighting the early failures of the U.S. testing program.
Around 103 million Americans—31% of the population—had been infected with Covid-19 by the end of 2020, according to models designed by Columbia University built on population data, recorded case numbers and the number of people testing positive for coronavirus antibodies.
The number of cases is far higher than what confirmed testing accounted for—CDC data puts this at around 20.5 million—the researchers said, making up just 22% of infections.
Jeffrey Shaman, a professor of environmental health sciences at Columbia University and one of the paper’s authors, said it is these undocumented cases, which are “often mild or asymptomatic infectious, that allow the virus to spread quickly through the broader population.”
The models show some parts of the country had far more infections than others, estimating more than 60% of people in areas including the Mississippi valley, Minnesota, Wisconsin, the Dakotas and Iowa to have caught Covid-19 by the end of 2020.
Several metropolitan areas studied by the researchers also showed very high proportions of people infected, including Los Angeles (52%), Chicago (48%), New York City (44%) and Miami (42%).
One of the most important tools needed to track and control the spread of any disease is a means of detecting it. The U.S., despite being in one of the best positions to do so, failed in this regard and its testing program was beset by a litany of logistical, technical and leadership issues. The model suggests 90% of cases were not identified by confirmed testing in March of last year and fewer than a quarter were by the end of the year. As cases across the U.S. rise with the spread of the highly infectious delta variant, officials are eager to boost testing capacity and the number of tests done each day are far below the levels carried out a year ago.
1 in 130. That’s how many Americans were contagious with Covid-19 on December 31, according to the researchers’ model. A similar proportion were likely infected but not yet contagious, the researchers wrote.
“While the landscape has changed with the availability of vaccines and the spread of new variants, it is important to recognize just how dangerous the pandemic was in its first year,” said researcher and co-author Sen Pei, an assistant professor of environmental health sciences at Columbia University.
What We Don’t Know
The model did not account for the possibility of people being infected with Covid-19 more than once, the possibility of waning immunity and of contagious new variants. All these factors will contribute towards the virus’ spread. Its findings are also, by their nature, retrospective estimates and cannot be completely confirmed.
What went wrong with coronavirus testing in the U.S. (Washington Post)
How The Pandemic Defeated America (Atlantic)