New study in antibody testing found more evidence that the coronavirus had been present in the United States since at least December 2019, weeks before the first confirmed case was announced on January 21, 2020.
The National Institutes of Health study analyzed 24,000 stored blood samples contributed by volunteers from across the country between January 2 and March 18, 2020.
Antibodies against the SARS-CoV-2 virus were detected through two different serological tests in nine patient samples, according to the work, published in the journal Clinical Infectious Diseases.
The participants were outside the main pockets of Seattle and New York, which are believed to be the main entry points for the virus in the United States.
The first positive samples came from participants in Illinois and Massachusetts on January 7 and 8, 2020, respectively, suggesting that the virus was present in those states in late December.
“Antibody testing of blood samples helps us better understand the spread of SARS-CoV-2 in the United States in the early days of the pandemic, when testing was restricted,” said lead author Keri Althoff, associate professor. of Epidemiology at the Johns Hopkins Bloomberg School of Public Health.
The research builds on a similar one published by the Centers for Disease Control and Prevention in November, which came to the same conclusion.
But since there is uncertainty surrounding serological testing, greater confirmation increases confidence in the finding.
To help minimize the chance of false positives, the team used two different tests on each sample, looking for antibodies that bind to different parts of the virus.
The types of antibodies sought are called immunoglobulin G, or IgG, which neutralize the ability of the virus to invade cells and do not appear until two weeks after a person is infected. It follows that the study participants with these samples were exposed to the virus at least several weeks before.
Limitations of the study include that the number of samples taken in many states was low, just a few dozen or hundreds in some cases.
Finally, there is the possibility that the antibodies they detected were formed against the infection of other coronaviruses, such as the four that cause the common colds.