When the pandemic truly ended daily life in the United States in March, many Americans described catching a bad cold or what they thought was the flu the previous winter and speculated that they could have caught COVID-19 – in some cases, before the US case was first confirmed in January.
New data from the United States Centers for Disease Control and Prevention suggest that this belief may not be so improbable. “CDC scientists found evidence of infection in 106 of 7,389 blood donations collected by the American Red Cross from residents of nine US states, according to the study published online in the journal Clinical Infectious Diseases. These samples used in study were collected between December 13, 2019 and January 17, 2020. Although this was only 1.4% of the Red Cross samples, this indicates that some Americans had already contracted SARS-CoV-2 before the first case confirmed, detected on January 19 in a traveler returning from China.
That being said . . . There’s always a very good chance that your bad cold or the flu from last winter was just a bad cold or the flu.
A study published last month in the Journal of the American Medical Association did a thorough 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 samples, the estimated percentage of people in a jurisdiction with detectable anti-SARS-CoV-2 antibodies ranged from less than 1 percent to 23 percent. Over 4 sampling periods in 42 of 49 jurisdictions with calculated estimates, less than 10 percent of people had detectable anti-SARS-CoV-2 antibodies.
The tests were conducted in all 50 states, the District of Columbia and Puerto Rico and selected from four time 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% – occurred in New York State during the first period, but “in almost all jurisdictions, less than 10% of people in the United States had evidence of previous SARS-CoV-2 infection using currently available commercial IgG assays. “
For much of the past year, we’ve seen arguments about whether official U.S. statistics give an accurate picture of the number of Americans who have caught the virus. Until the tests were widely available, they were mostly self-selected – Americans looked for a test or ended up sick in the hospital and got tested. The theory was that there were a significant number of asymptomatic or minimally symptomatic Americans who were not going to be tested – and that discussions about the positivity rate of coronavirus tests missed large swathes of Americans who have caught the virus, were asymptomatic and probably never knew they caught it. A good number of people thought that meant that collective immunity had been reached or that collective immunity was imminent.
If we have about ten percent of the population testing positive for antibodies, as this JAMA study suggests, and we had three weeks of 140,000 or more new infections per day, so no, we’re not that close to collective immunity. At least not yet.