Research shows that one-third of Americans will be infected with COVID-19 in 2020
Undocumented cases account for about three-quarters of infections
A new study published in the journal nature It is estimated that 103 million Americans (31% of the U.S. population) have been infected with COVID-19 by the end of 2020. Researchers at Columbia University modeled the spread of the coronavirus and found that less than a quarter of infections — only 22 percent — were confirmed by public health reports based on testing.
This study comprehensively quantifies the overall burden and characteristics of COVID-19 in the United States in 2020 for the first time. Researchers used population, mobility, and confirmed case data to simulate the spread of SARS-CoV-2 within and between all 3,142 counties in the United States.
Jeffrey Saman, a professor at the University’s Melman School of Public Health, which is affiliated with the Earth Institute, said: “The vast majority of infectious diseases are not explained by the number of confirmed cases.” “It is these undocumented cases, usually It is a mild or asymptomatic infectious case that enables the virus to spread rapidly among a wider range of people.”
Studies have found that infections are more common in certain areas of the country. In the upper Midwest and the Mississippi Valley, including Dakota, Minnesota, Wisconsin, and Iowa, it is estimated that more than 60% of the population will be infected by the end of 2020. Of the five metropolitan areas examined by the researchers, 48% of residents in Chicago, 52% in Los Angeles, 42% in Miami, 44% in New York City, and 27% in Phoenix were infected during the same time period.
Researchers say that over time, more and more infected people have received more and more tests, but still provide incomplete information. The proportion of confirmed cases reflected in the research estimates rose from 11% in March to 25% in December; this reflects the improvement of testing capabilities, the relaxation of initial restrictions on test use, and the increase in public recognition, attention, and concern. However, the detection rate is still far below 100%, because people with mild or asymptomatic infections may still transmit the virus and are therefore unlikely to be tested.
The study further found that as of December 31, 2020, approximately 1 in 130 Americans (0.77%) were infected with the virus. It is estimated that a similar proportion (0.83%) is infected but not yet infected. However, in some metropolitan areas, the percentage of individuals who are infectious at the end of the year is much higher.
With the strengthening of treatment and public health measures, the mortality rate has declined. The percentage of infected people who died of COVID-19 dropped from 0.8% during the spring wave to 0.3% at the end of the year. Urban areas such as New York City that peaked in the spring had the worst numbers due to delays in test availability and mask requirements, overwhelmed hospitals, and lack of effective treatments.
Different cities reach their peaks at different times of the year. New York and Chicago experienced strong spring and fall/winter waves, but few summer activities; Los Angeles and Phoenix experienced summer and fall/winter waves; and Miami experienced all three waves. Los Angeles County is the largest county in the United States, with a population of more than 10 million. The disasters are particularly severe in autumn and winter. The community infection rate on December 31 was 2.4%.
Looking to the future, the author writes, there are several factors that will change the population’s susceptibility to infection. The virus will continue to spread to people who have not yet been infected. Although vaccines can prevent serious and fatal diseases, breakthrough infections, including those with mild or asymptomatic infections, will promote the spread of the virus. Although there is evidence that antibodies may weaken over time, and some people must have been re-infected, the study did not consider the possibility of re-infection in people who already have the disease. The authors write that new and more infectious mutations will make reinfection and breakthrough infections more likely.
Mailman Assistant Professor of Environmental Health Sciences Sen Pei said: “Although the situation has changed with the advent of vaccines and the spread of new variants, it is important to recognize the danger of the pandemic in the first year.”
Other authors include Teresa K. Yamana, Sasikiran Kandula, and Marta Galanti, all of whom are members of Mailman School. The research was supported by the National Science Foundation and the Morris Singer Foundation.
Adapted from a press release from the Postman School of Public Health.
