A new study estimates that nearly a third of the U.S. population — 103 million Americans — may have received COVID-19 by the end of 2020, with only a fraction of these cases correctly reported in public health reports.
Columbia University Mailman School of Public Health researchers found that people with mild or no symptoms were unlikely to report their infections and exacerbated the spread of the virus in a new study published Thursday in the journal Nature.
“The vast majority of infections were not accounted for by the number of confirmed cases,” Jeffrey Shaman, a professor of environmental health at Columbia University’s Mailman School of Public Health, said in a news release. “It is these undocumented cases, which are often mild or asymptomatic infectious, that allow the virus to spread rapidly through the wider population.”
The rate at which probable cases were confirmed – the “detection rate” – increased from 11 percent to 25 percent from March to December, as testing for availability and accuracy increased.
At the same time, mortality fell from 0.8 percent to 0.3 percent.
The study found that certain parts of the country experienced increased infection rates: Over 60 percent of the population in the Upper Midwest and Mississippi Valley, including North and South Dakota, Minnesota, Wisconsin and Iowa, became infected by the end of the year, it found.
Researchers analyzed five major metropolitan areas, finding that 52 percent of Los Angeles residents, 48 percent of Chicago, 44 percent of New York City, 44 percent of Miami and 27 percent of Phoenix had contracted the virus by the end of 2020.
The study found seasonal increases in the virus in each city, with strong increases in the spring and fall / winter in New York and Chicago, while calming down in the summer. Alternatively, LA and Phoenix underwent summer and fall / winter waves. Miami experienced all three, the student found.
“Although the landscape has changed with the availability of vaccines and the spread of new varieties, it is important to recognize how dangerous the pandemic was in its first year,” said Sen Pei, PhD, assistant professor of environmental health sciences at Columbia University Mailman School of Public Health, in the publication.
Admissions this week reached levels not seen since January, with over 100,000 COVID-19 admissions reported Thursday.
The wave comes amid the fourth wave of the virus and its highly contagious Delta variant, which killed 1,456 Americans Wednesday, according to Johns Hopkins data. The daily record high of 4,460 was set on January 12th.