According to a new study, COVID-19 arrived in the United States last December without anyone knowing

The Providence Regional Medical Center in Everett, Washington, on January 21st. According to the Washington Department of Health, the first known COVID-19-infected person was observed in the United States at that time. (Photo by Jason Redmond / AFP)

It is a widely accepted fact that the first case of clinically diagnosed COVID-19 in the U.S. was in Washington state in late January. However, a new study suggests that the virus may have been circulating here as early as mid-to-mid-December 2019 without anyone noticing.

The study, carried out by researchers at the Center for Disease Control and Prevention and published in the journal Clinical infectious diseases, analyzed the American Red Cross blood donation collected by nine states. The researchers discovered evidence of coronavirus antibodies in 106 of the 7,389 blood donations collected between December 13 and January 17.

Antibodies are proteins produced by the immune system to fight infections such as viruses, according to the Food and Drug Administration. They can also help prevent future illnesses from specific infections. The presence of certain antibodies in the blood suggests that a person has been exposed to a particular virus or bacterium – in this case COVID-19, says Dr. Amesh A. Adalja, a senior scientist at the Johns Hopkins Health Security Center, told Yahoo Life.

The researchers found antibodies to SARS-CoV-2, the virus that causes COVID-19, in 39 samples from December 13, 2019, from California, Oregon, and Washington. Iowa, Massachusetts, Michigan, Rhode Island and Wisconsin in early January.

“These findings suggest that SARS-CoV-2 may have been imported into the United States before January 19, 2020,” the researchers concluded.

The researchers also said their findings suggest that “isolated SARS-CoV-2 infections may have occurred in the western United States earlier than previously recognized, or that a small portion of the population may have antibodies earlier” against the virus.

However, there is a big “but” here.

The researchers noted in the article that there have been cross-reactive antibody responses between SARS-CoV-2 and some other common human coronaviruses in the past. “The antibodies we found may have been from SARS-CoV-2 infections or common coronavirus infections,” says Natalie J. Thornburg, co-author of the study and CDC researcher at Yahoo Life.

“Some antibody tests, especially those with lower specificity for SARS-CoV-2, may produce particularly false positive results due to cross-reactivity with other cold-causing coronaviruses,” said Dr. Prathit Kulkarni, professor of infectious medicine at Baylor College of Medicine. says Yahoo Life.

However, the authors tried to control this by screening for certain types of coronaviruses. “Some, but not all, of the positive samples are very strongly positive for SARS-CoV-2 using multiple tests and are therefore more likely to be derived from SARS-CoV-2 infections,” says Thornburg.

As a result, the study cannot definitively say whether there were COVID-19 cases in the United States before the end of January. That can be hard to prove, Kulkarni says. “Without widespread testing in January and February 2020, it’s hard to know exactly how much SARS-CoV-2 may have spread in the United States at the time,” he says.

Nevertheless, many experts believe that the virus was present even before it was actually detected.

“There were clearly cases before the first ones were recognized,” Adalja says. “This study provides plenty of clues, but there is a big caveat that there may be antibodies to other seasonal coronaviruses.”

Adalja said the results of the study “suggest” that the virus had been in the United States for weeks before it was detected, but “we still need more data.”

Dr. Richard Watkins, a physician for infectious disease in Akron, Ohio, and a professor of internal medicine at Northeast Ohio Medical University, agrees. “It seems reasonable to conclude,” the virus was present in the U.S. before the end of January, he tells Yahoo Life. “This is a new disease, and then there were no laboratory tests to diagnose it in the United States,” – he points out.

As for why the virus didn’t spread earlier in the United States when it was actually here, Adalja said the cases could simply be “deadlock infections”. He adds, “Not all cases will spread.”

It is also possible that the virus is widespread in the country but has been described as a cold or flu. “They may not have been noticed, especially during colds and flu,” Adalja says.

Another factor to consider, according to Adalja: Cases of a particular virus are often only detected when they begin hospitalization. “People in vulnerable populations need to be transported to hospitals in a sufficient number of cases to be noticed,” he says. It is possible that many early cases of COVID-19 did not cause serious illness and, as a result, did not alert health professionals, Adalja says.

That makes a big difference, ”says Dr. Lewis S. Nelson, a professor and president of the Department of Emergency Medicine at Rutgers Medical School in New Jersey, Yahoo Life. “If you don’t search, you won’t find it,” he says. “But when we went out to look, we found him.”

Thornburg said it is difficult to know how widespread the virus is in the United States in December and early January. “The data does not suggest widespread traffic, but instead sporadic rare cases,” he says.

While there is still some uncertainty about exactly when the virus began to spread in the United States, experts generally agree that it happened sooner than most people realize. “Many in the industry believe that there were probably COVID-19 cases in the United States before January,” Adalja says.

Determining the exact date the virus arrived in the U.S. now has no huge impact on things, Kulkarni says. “In practical terms, this doesn’t change much of what we should be doing now, continuing with standard public health measures and introducing a national vaccination plan,” he says.

Dr. Peter Winklestein, executive director of the Institute of Health Informatics at Jacobs School of Medicine and Medicine at the University of Buffalo, tells Yahoo Life that this also does not increase the chances of the herd developing immunity to the virus. “There’s nothing to support that,” he says. “The latest results are interesting facts, but we are nowhere near the herd’s immunity. If you think you had the virus last December, then hell you can’t consider yourself Superman.

THE latest coronavirus news and updates, follow along Experts say people over 60 and immunocompromised people are still at risk. If you have any questions, please read CDCand WHO resource guides.

Learn more about Yahoo Life

Want to get lifestyle and wellness news in your inbox? Register here to the Yahoo Life newsletter.