In a new study, researchers found that by Nov. 15 of last year, roughly 47 million Americans—about 14.5% of the U.S. population—had already been infected with the new coronavirus.
That’s much higher than the close to 11 million known U.S. cases of infection that were recorded by that date.
The researchers suggest at least 40% of all infections are thought to be asymptomatic.
The research was conducted by a team at Pfizer Vaccines.
It’s believed that everyone who becomes infected with the new coronavirus will develop some form of immunity.
And if enough of the population (about 70%) were to gain immunity—either through infection or vaccination—so-called “herd immunity” would set in, thwarting the virus’ ability to spread further.
But the numbers for Nov. 15, 2020 show that herd immunity is still far away.
Findings of this study suggest that although more than 14% of the U.S. population was infected with SARS-CoV-2 by mid-November, a substantial gap remains before herd immunity can be reached.
In the study, the team analyzed data from four “seroprevalence” (blood test) surveys conducted by the U.S. Centers for Disease Control and Prevention in April, May, June, July and August.
These surveys were conducted in 10 states (California, Connecticut, Florida, Louisiana, Minnesota, Missouri, New York, Pennsylvania, Utah and Washington).
A fifth CDC survey was conducted in 47 states nationwide.
All of that data helped the researchers estimate the level of “under-reporting” of coronavirus infections—the gap between the number of people recorded as having COVID-19 and the larger “true” number of cases.
The team used those calculations to come up with an estimated number of 46,910,006 cases of SARS-CoV-2 infection having occurred among Americans by Nov. 15, 2020.
They stressed that the COVID-19 pandemic is not a static phenomenon, so these calculations will change over time as the proportion of persons with infection tested, diagnosed and reported changes.
One author of the study is Dr. Frederick Angulo.
The study is published in JAMA Network Open.
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