A THIRD of Americans were infected with COVID-19 by the end of 2020, research shows

A THIRD of Americans were infected with COVID-19 by the end of 2020, research shows

  • About 100 million Americans, nearly a third of the population, will have contracted COVID-19 sometime in 2020, a new study finds
  • With 34.4 million officially recorded cases, infections were undercounted by more than 60%
  • At one point in early December, about 1% of the population was simultaneously Covid-positive
  • In some areas, more than 60% of people contracted the virus last year


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COVID-19 may have infected more Americans by 2020 than previously believed, a new study finds.

Researchers from the Columbia University Mailman School of Public Health simulated transmission of the virus across the country and found that 31 percent of the country’s population had contracted the virus sometime last year.

This means there could have been about 100 million cases in the US last year, compared to the official count of 34.4 million — an undercount of nearly 66 percent.

In some areas, more than 60 percent of the population was infected.

The team says the simulation also showed that nearly 80 percent of cases may have gone undetected.

A study shows that the number of COVID-19 cases in the US may have been underestimated by 66 million last year and that nearly a third of the population was infected last year. At the beginning of last year, things were significantly undervalued. The blue bars in the chart represent the estimated “true” number of cases in 2020, with numbers on the x-axis corresponding to the month of the year from which the data was collected (“3” represents March). The orange bars represent the official number of cases

At some point in late 2020, more than 1% of Americans had COVID-19 at the same time.  The orange line in the chart shows the proportion of US residents who are expected to have the virus.  The blue line represents the official number of confirmed cases

At some point in late 2020, more than 1% of Americans had COVID-19 at the same time.  The orange line in the chart shows the proportion of US residents who are expected to have the virus.  The blue line represents the official number of confirmed cases

At some point in late 2020, more than 1% of Americans had COVID-19 at the same time. The orange line in the chart shows the proportion of US residents who are expected to have the virus. The blue line represents the official number of confirmed cases

For the study, published in Nature, researchers built a model that spanned all 3,142 counties in the US

Using population, case data and mobility between provinces, they estimate how the virus would spread across the country.

In Midwestern and Mississippi Valley areas — states around the Mississippi River that include Kentucky, Missouri and Tennessee — more than 60 percent of residents were infected with COVID-19.

Los Angeles was also hit particularly hard, according to the simulation, with more than 52 percent of people contracting the virus.

In other major cities, a large percentage of residents became ill, including 42 percent of Chicago residents, 42 percent in Miami and 44 percent in New York City.

Cases that went undetected were often early in the pandemic, when testing was limited and some were less alert to symptoms.

Tests also became less scarce.

In March 2020, when the pandemic first began, researchers estimated that only 11 percent of cases were detected.

In December, about 25 percent of cases were detected.

“The vast majority of infectious diseases were not explained by the number of confirmed cases,” said Dr. Jeffrey Shaman, a professor of environmental health sciences at Columbia University Mailman School of Public Health.

“It is these undocumented cases, which are often mildly or asymptomatically contagious, that allow the virus to spread rapidly through the wider population.”

At its highest point in early December last year, more than one percent of Americans were simultaneously infected with the virus.

Researchers also found that different cities were also affected by the pandemic at different times.

For example, New York City and Chicago were hit during the first spring wave of the pandemic, but dodged the bigger wave of summer 2020.

Los Angeles and Phoenix didn’t suffer too much at the start of the pandemic, but were inundated with cases in the summer of 2020 and during the winter wave late in the year.

Miami, along with much of the rest of Florida, experienced business spikes during all three waves.

This isn’t the first time researchers have found cases in the US were undervalued last year.

A University of Washington study last month found that the number of cases was understated by 60 percent and that the true number could rise to 86 million.

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