Story at a glance:
- Researchers estimate that nearly one-third of the U.S. population, or 103 million Americans, got COVID-19 last year.
- Nearly half the residents of Chicago, Los Angeles, Miami and New York City were likely infected in 2020, according to a new analysis.
- In a year to year comparison, starting from spring 2020 to spring 2021, the percentage of people who died from COVID-19 dropped from 0.8 to 0.3 nationwide.
While official numbers report nearly 20 million confirmed cases of COVID-19 last year, according to The COVID Tracking Project, researchers estimate that nearly one-third of the U.S. population, 31 percent or 103 million Americans, had COVID-19 at some point last year.
Columbia University Mailman School of Public Health researchers determined that fewer than one-quarter, 22 percent, confirmed their positive diagnosis for public health reports through testing, according to a news release by the American Association for the Advancement of Science (AAAS).
In the upper Midwest and Mississippi valley, including the Dakotas, Minnesota, Wisconsin and Iowa, nearly two-thirds, 60 percent, of the population was estimated to have had COVID-19 in 2020. Meanwhile, nearly half the residents of Chicago, Los Angeles, Miami and New York City (48 percent, 52 percent, 42 percent and 44 percent, respectively) were likely infected in 2020, according to the study published in the journal Nature.
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Of course, the timing of each city’s peak of contagion varied, and some experienced several spikes. During the spring and winter months, the study found, New York City and Chicago were dealt a heavy blow, but little activity occurred during the summer. Los Angeles, Miami and Phoenix, meanwhile, experienced all three seasonal waves. Los Angeles County, the largest county in the U.S. with a population of more than 10 million people, was hit particularly hard with an infection rate of 2.4 percent at the end of 2020.
Considering these numbers, in a year to year comparison starting from last spring, the percentage of people who died from COVID-19 dropped from 0.8 to 0.3 nationwide. That number was much worse in metropolitan areas due to the city delays in testing availability, overwhelmed hospitals and a lack of effective treatments. Throughout the year, however, increased numbers of confirmed cases reflected improved testing capacity, "a relaxation of initial restrictions on test usage and increasing recognition, concern, and care-seeking among the public."
From March to December, the ascertainment rate — or the amount of likely cases that were confirmed — more than doubled from 11 percent to 25 percent, but still fell short as individuals with mild or asymptomatic infections could still spread the virus without knowing.
“The vast majority of infections were not accounted for by the number of confirmed cases,” said Jeffrey Shaman, a professor of environmental health sciences at Mailman School of Public Health, in the release. “It is these undocumented cases, which are often mild or asymptomatic infectious, that allow the virus to spread quickly through the broader population.”
The findings suggest that the virus will continue to spread and those who have not yet been vaccinated will likely suffer the most.
“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 Sen Pei, an assistant professor of environmental health sciences at Mailman School of Public Health, in the release.
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