When the pandemic really shut down U.S. daily life in March, lots of Americans described getting either a bad cold or what they thought was the flu the previous winter and speculated that they may have caught COVID-19 — in some cases, before the first confirmed U.S. case in January.
New data from the U.S. Centers for Disease Control and Prevention suggest that belief may not be so unlikely. “Scientists at the CDC found evidence of infection in 106 of 7,389 blood donations collected by the American Red Cross from residents in nine states across the U.S., according to the study published online in the journal Clinical Infectious Diseases.” These samples used in the study were collected between December 13, 2019 and January 17, 2020. While that’s only 1.4 percent of the Red Cross samples, it does indicate that some Americans had already caught SARS-CoV-2 before the first confirmed case, detected on January 19 in a returned traveler from China.
With that said . . . there’s still a really good chance that your bad cold or the flu last winter was just a bad cold or the flu.
A study published last month in the Journal of the American Medical Association did an extensive study of antibody tests and found . . . so far, only a small fraction of Americans have caught the virus and have the antibodies:
In this repeated, cross-sectional study of 177,919 residual clinical specimens, the estimated percentage of persons in a jurisdiction with detectable SARS-CoV-2 antibodies ranged from fewer than 1 percent to 23 percent. Over 4 sampling periods in 42 of 49 jurisdictions with calculated estimates, fewer than 10 percent of people had detectable SARS-CoV-2 antibodies.
The tests were conducted across all 50 states, the District of Columbia, and Puerto Rico and selected from four periods: July 27 to August 13, August 10 to August 27, August 24 to September 10, and September 7 to September 24, 2020.
The highest prevalence of antibodies — 23.3 percent — came in New York State in the first period, but “in nearly all jurisdictions, fewer than 10 percent of people in the US had evidence of previous SARS-CoV-2 infection using currently available commercial IgG assays.”
For much of this past year, we’ve seen arguments about whether the U.S. official statistics were giving an accurate picture of just how many Americans had caught the virus. Up until testing became widely available, it was mostly self-selecting — Americans either sought out a test, or ended up sick in a hospital and were tested. The theory was that there were significant numbers of Americans who were either asymptomatic or minimally symptomatic who were not going to get tests — and that discussions of the positivity rate of coronavirus tests missed vast swaths of Americans who caught the virus, were asymptomatic, and probably never knew they caught it. Quite a few folks believed that this meant that either herd immunity had been reached or reaching herd immunity was imminent.
If we have about ten percent of the population testing positive for antibodies, as that JAMA study suggests, and we have had three weeks of 140,000 or more new infections per day, then no, we are not that close to herd immunity. At least, not yet.