The number of people infected with COVID-19 in the United States may be six to 24 times higher than reported, depending on the region of the country, according to a study published Tuesday by the Centers for Disease Control and Prevention (CDC) in JAMA Internal Medicine.
Across the country, at least 10 times more people have been infected with SARS-CoV-2, the virus that causes COVID-19, than has been previously reported, the CDC researchers conclude.
The study’s estimates are based on COVID-19 antibody tests performed on routine blood samples taken from 16,025 people in 10 regions across the U.S. The tests were done for non-coronavirus-related medical reasons.
The COVID-19 cases identified in the samples “likely include asymptomatic and mild infections for which health care was not sought, as well as symptomatic infections in persons who either did not seek care or in whom SARS-CoV-2 viral testing was not performed,” the researchers explain.
These findings demonstrate that the official count of COVID-19 cases in the United States vastly underestimates the true scope of the pandemic. Nearly 4 million cases have been confirmed in the U.S. since the country reported its first one in late January. This new study suggests the actual number exceeds 40 million.
Yet, the findings also underscore that the country is a long way off from herd immunity — when enough people are immune to the virus to help stave off its spread among the general population. Most experts say that at least 60 percent of a population would need to have had COVID-19 for herd immunity to kick in. Not only is the rate of infection in the U.S. far below that figure, scientists are still unsure if all people who recover from COVID-19 develop immunity, or for how long.
Minnesota — specifically, the Minneapolis/St. Paul/St. Cloud area — was one of the regions included in the study. The CDC researchers estimate that 10.2 times more Minnesotans have been infected with COVID-19 than reported.
With 47,000-plus confirmed cases in the state, Minnesota’s actual number may exceed 470,000, the study suggests.
The estimated infection rates for the other regions in the study were as follows:
- Connecticut: 6.0 times higher than reported
- Philadelphia metro area: 6.8 times higher
- San Francisco Bay area: 9.0 times higher
- Utah: 10.5 times higher
- South Florida: 11.2 times higher
- Western Washington: 11.2 times higher
- New York City metro area: 11.9 times higher
- Louisiana: 15.7 times higher
- Missouri: 23.8 times higher
Limitations and implications
As an editorial that accompanies the study points out, the blood samples used for this research were collected from March to early May, a time when stay-at-home orders were in place in many areas and, therefore, when few people were seeing their doctor for routine tests or elective procedures. The individuals whose samples were used in this study may not be representative, therefore, of the general population.
In addition, the last of the samples were taken almost two months ago, so they may not be indicative of current rates of infection.
Still, the study’s findings highlight the urgent need for widespread testing to identify asymptomatic cases that are going undetected and silently spreading the disease, write the editorial’s authors, Drs. Tyler Brown and Rochelle Walensky of Boston’s Massachusetts General Hospital.
The study’s findings also offer a rebuke to the idea that herd immunity is going to help stem the spread of COVID-19 anytime soon, they add.
“The size of the epidemic projected through early May 2020 in this study falls far short of the estimated herd immunity threshold of approximately 60% to 70%,” Brown and Walensky point out. “[Seven] of the 10 study locations are currently experiencing substantial, as-yet uncontrolled increases in new COVID-19 cases.”
“These data should also quickly dispel myths that dangerous practices like ‘COVID parties’ are either a sound or safe way to promote herd immunity,” they add.
What the study shows is that everybody needs to remain vigilant.
“Because persons often do not know if they are infected with SARS-CoV-2, the public should continue to take steps to help prevent the spread of COVID-19, such as wearing cloth face coverings when outside the house, remaining 6 feet apart from other people, washing hands frequently, and staying home when sick,” the CDC researchers conclude.
FMI: You’ll find the study on JAMA Internal Medicine’s website. The CDC has also produced an interactive dashboard with data from the 10 sites in the study (including Minnesota), which the agency says it will update regularly.