Coronavirus Infected One-Third of Americans in 2020

Aug. 26, 2021 — About one third of the US population had been infected with coronavirus 2 by the end of 2020, according to a new study published today in Nature.

Jeffrey Shaman, PhD, director of the Climate and Health Program at Columbia University, and colleagues simulated the spread of coronavirus within all 3,142 counties in the United States.

The United States had the highest number of confirmed COVID-19 cases and deaths in the world during 2020. More than 19.6 million cases were reported by the end of the year.

But the authors point out “69% of the population remained susceptible to viral infection.”

‘We Have Not Turned the Corner’

Jill Foster, MD, a pediatric infectious disease doctor at the University of Minnesota Medical School, Minneapolis says the study adds evidence that : “We have not turned the corner on COVID-19 and are nowhere near herd immunity — if it exists for SARS-CoV-2.”

She said the numbers presented are particularly concerning in regard to how many people were susceptible and were actively able to infect others: “Much higher than most people imagined and very much higher than their comparison, influenza. “There are still more people susceptible than we had believed,” Foster added. “If the pattern continues where the Delta variant infects a significant portion of those vaccinated, the number of people susceptible rises even higher than was predicted.”

Foster said these numbers represent a warning that COVID should be treated as a continuing threat.

“We need to acknowledge that there is COVID-19 infection simmering and periodically erupting throughout the country,” she said. “It is not monolithic and varies by geography and seasons in ways that are difficult to predict other than at any given time there is likely more infection present than we are identifying and more people susceptible to infection than we have calculated.”

Fatality Rates Dropped

Some of the data showed good news, Shaman says. The infection death rate fell from 0.77% in April to 0.31% in December. The authors suggest that that may be because of improvements in diagnosis and treatment, patient care, and reduced disease severity.

However, the rate of death was still nearly four times as high as the estimated death rate for the flu (0.08%) and the 2009 flu pandemic (0.0076%), the authors point out.

Joe K. Gerald, MD, , program director with public health policy and management at University of Arizona in Tucson, says this study helps confirm that COVID-19 is much deadlier than the flu and that the intensity of the response has been appropriate.

“We should be willing to invest a lot more in mitigating COVID-19 than seasonal influenza because it has much greater consequences,” he said.

The numbers help emphasize that testing must improve. “We didn’t have enough tests available, and they weren’t easily accessible. For much of the year we were flying in the dark,” Gerald said.

The number of tests has increased this year, he acknowledged, but testing still lags.

“We just can’t miss this many infections or diagnoses and hope to gain control,” he said.

The study also points out the huge variation by state and even by county in infections and deaths, and that variation continues. Gerald noted that the numbers make it difficult for some regions to accept broader mandates, because the threat from COVID-19 appears very different where they are.

“We have to think about regions, how many people are susceptible, and what the testing capacity is,” he said. “States and even counties should have some leeway to make some important public health decisions, because local conditions are going to differ at different points in time.”