One in three Americans had COVID-19 by the end of 2020, study estimates
Undocumented infections accounted for estimated three-quarters of
infections last year

Date:
August 26, 2021
Source:
Columbia University's Mailman School of Public Health
Summary:
A new study estimates that 103 million Americans, or 31 percent
of the U.S. population, had been infected with SARS-CoV-2 by the
end of 2020.

Researchers modeled the spread of the coronavirus, finding that
fewer than one-quarter of infections (22 percent) were accounted for
in cases confirmed through public health reports based on testing.



FULL STORY ==========================================================================
A new study published in the journal Nature estimates that 103 million Americans, or 31 percent of the U.S. population, had been infected with
SARS- CoV-2 by the end of 2020. Columbia University Mailman School of
Public Health researchers modeled the spread of the coronavirus, finding
that fewer than one- quarter of infections (22%) were accounted for in
cases confirmed through public health reports based on testing.


==========================================================================
The study is the first to comprehensively quantify the overall burden
and characteristics of COVID-19 in the U.S. during 2020. The researchers simulated the transmission of SARS-CoV-2 within and between all 3,142
U.S. counties using population, mobility, and confirmed case data.

Infections were more widespread in some areas of the country In areas
of the upper Midwest and Mississippi valley, including the Dakotas,
Minnesota, Wisconsin and Iowa, more than 60 percent of the population is estimated to have been infected by the end of 2020. In five metropolitan
areas the researchers examined, 48 percent of residents of Chicago,
52 percent of Los Angeles, 42 percent of Miami, 44 percent of New York
City, and 27 percent of people in Phoenix, had been infected in the
same timeframe.

Testing picked up on a growing number of infections but offered an
incomplete picture The portion of confirmed cases reflected in the
study's estimates, i.e. the ascertainment rate, rose from 11 percent in
March to 25 percent in December, reflecting improved testing capacity,
a relaxation of initial restrictions on test usage, and increasing
recognition, concern, and care-seeking among the public. However,
the ascertainment rate remained well below 100 percent, as individuals
with mild or asymptomatic infections, who could still spread the virus,
were less likely to be tested.



==========================================================================
"The vast majority of infectious were not accounted for by the
number of confirmed cases," says Jeffrey Shaman, PhD, professor of environmental health sciences at Columbia University Mailman School of
Public Health. "It is these undocumented cases, which are often mild or asymptomatic infectious, that allow the virus to spread quickly through
the broader population." One in 130 Americans was contagious at year's
end Roughly 1 in 130 Americans (0.77%) was contagious with SARS-CoV-2
on December 31, 2020. A similar percentage (0.83%) was estimated to
be latently infected, i.e. infected but not yet contagious. In some metropolitan areas, the percentage of individuals who was contagious at
year's end was much higher.

Fatality rates fell with strengthening treatments and public health
measures The percentage of people with infections who died from COVID-19
fell from 0.8 percent during the spring wave to 0.3 percent by year's
end. Urban areas like New York City that peaked in the spring saw the
worst numbers for reasons that include delays in testing availability and masking mandates, overwhelmed hospitals, and lack of effective treatments.



========================================================================== Cities peaked at different times of the year New York and Chicago
experienced strong spring and fall/winter waves but little activity during summer; Los Angeles and Phoenix underwent summer and fall/ winter waves;
and Miami experienced all three waves. Los Angeles County, the largest
county in the U.S. with a population of more than 10 million people,
was particularly hard-hit during the fall and winter and had a community infection rate of 2.4 percent on December 31.

A new pandemic landscape for 2021 Looking ahead, the authors
write that several factors will alter population susceptibility to
infection. The virus will continue to spread to those who haven't yet
been infected. While vaccines protect against severe and fatal disease, breakthrough infections, including those that are mild or asymptomatic,
will contribute to the spread of the virus. The current study does
account for the possibility of reinfection, although there is evidence
of waning antibodies and reinfection. New more contagious variants make reinfection and breakthrough infections more likely.

"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," concludes Sen Pei,
PhD, assistant professor of environmental health sciences at Columbia University Mailman School of Public Health.

Additional authors include Teresa K. Yamana, Sasikiran Kandula, and
Marta Galanti at Columbia Mailman School.

The study was supported by funding from the National Science Foundation
(DMS- 2027369) and a gift from the Morris-Singer Foundation. Human
mobility data was provided by SafeGraph. Shaman and Columbia University disclose partial ownership of SK Analytics. Shaman discloses consulting
for Business Network International (BNI).

========================================================================== Story Source: Materials provided by Columbia_University's_Mailman_School_of_Public_Health.

Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Sen Pei, Teresa K. Yamana, Sasikiran Kandula, Marta Galanti, Jeffrey
Shaman. Burden and characteristics of COVID-19 in the United States
during 2020. Nature, Aug. 26, 2021; DOI: 10.1038/s41586-021-03914-4 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/08/210826111744.htm

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