Undocumented infections accounted for an estimated three-quarters of last year’s infections-ScienceDaily

New research published in the journal Nature By the end of 2020, it is estimated that 103 million Americans, or 31% of the US population, will be infected with SARS-CoV-2. Researchers at Columbia University’s Merman School of Public Health modeled the epidemic of the coronavirus, and one-quarter (22%) of infections were described in cases identified through test-based public health reports.

This is the first study to comprehensively quantify the overall burden and characteristics of COVID-19 in the United States in 2020. Researchers used population, mobility, and confirmed case data to simulate the transmission of SARS-CoV-2 within and between all 3,142 counties in the United States. ..

The infection was more widespread in some parts of the country

It is estimated that more than 60% of the population will be infected by the end of 2020 in the Midwest and upper Mississippi Valley areas, including Dakotas, Minnesota, Wisconsin, and Iowa. 52 percent of Chicago residents, 52 percent of Los Angeles, 42 percent of Miami, 44 percent of New York City, and 27 percent of Phoenix people were infected in the same time frame.

Tests picked up more and more infections, but provided an incomplete overview

The portion of confirmed cases reflected in the survey estimates, or confirmation rate, was 11% in March, reflecting increased test capacity, relaxation of initial restrictions on the use of the test, awareness, concerns, and increased care. It rose to 25% in December. -I’m looking for it among the general public. However, confirmation rates were well below 100%, as individuals with mild or asymptomatic infections that could spread the virus were less likely to be tested.

“The majority of infectious diseases were not explained by the number of confirmed cases,” says Dr. Jeffrey Sherman, a professor of environmental health sciences at Columbia University’s Mailman School of Public Health. “These undocumented cases are often mild or asymptomatic infectious and allow the virus to spread rapidly to a wider population.”

1 in 130 Americans were infected at the end of the year

On December 31, 2020, about 1 in 130 Americans (0.77%) was infected with SARS-CoV-2. It was estimated that a similar proportion (0.83%) was potentially infected, that is, infected but not yet infected. In some metropolitan areas, the proportion of individuals infected at the end of the year was much higher.

Case fatality rate decreased due to increased treatment and public health measures

The proportion of infectious disease patients who died of COVID-19 decreased from 0.8% in the spring wave to 0.3% by the end of the year. Urban areas such as New York City, which peaked in the spring, have seen the worst numbers due to delays in availability testing and masking of mandates, overwhelming hospitals, and lack of effective treatments. I did.

The city peaked at various times of the year

New York and Chicago experienced strong spring and autumn / winter waves, but were less active during the summer. Los Angeles and Phoenix received summer and autumn / winter waves. And Miami experienced all three waves. Los Angeles County, the largest county in the United States with a population of over 10 million, was hit particularly hard in the fall and winter, with a regional infection rate of 2.4% on 31 December.

2021 new pandemic landscape

Looking to the future, the authors write that several factors will change the population’s susceptibility to infection. The virus continues to spread to people who have not yet been infected. Vaccines protect against serious and deadly illnesses, but breakthrough infections, including mild or asymptomatic ones, contribute to the spread of the virus. Current studies have evidence of antibody depletion and reinfection, but explain the potential for reinfection. Newer, more contagious variants increase the likelihood of reinfection and breakthrough infections.

“The situation has changed with the availability of vaccines and the spread of new variants, but it’s important to recognize how dangerous the pandemic was in the first year,” said Dr. Sempei, an assistant professor of environmental health sciences at Columbia University. I conclude. Mailman School of Public Health.

Additional authors include Teresa K. Yamana, Sashiki Lankandura, and Malta Galanti of the Columbia Mailman School.

This research was supported by funding from the National Science Foundation (DMS-2027369) and donations from the Morris Singer Foundation. Human mobility data was provided by SafeGraph. Sherman and Columbia University disclose partial ownership of SK Analytics. Sherman discloses Business Network International (BNI) consulting.

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