The analysis is not final as some experts continue to be skeptical. But federal health officials are increasingly accepting a timeline during which a small number of COVID-19 infections may have occurred in the United States, before the world became aware of a dangerous new virus that exploded in China.
“Studies reach the same conclusion”, says Natalie Thornburg of the Centers for Disease Control and Prevention, CDC.
“It is likely that there have been very rare and sporadic cases before we were aware of it. “But it was not widespread and did not spread until the end of February.” adds Ms. Thornburg, lead researcher on the immunology team for the respiratory virus.
The coronavirus, which turned into a pandemic, appeared in Wuhan, China in late 2019. Officially, the first infection identified in the United States was a person from Washington state who returned from Wuhan on January 15 and sought medical help. at a clinic on January 19th.
CDC officials initially said the virus outbreak in the United States occurred over a three-week period from mid-January to early February. But research since then – including research by the CDC – has suggested that a small number of infections have occurred earlier.
A CDC-led study published in December 2020 that analyzed 7,000 blood samples donated to the American Red Cross suggests that some Americans had been infected with the virus since mid-December 2019.
The latest study, published online Tuesday by the journal Clinical Infective Diseases, was conducted by a team of researchers from the National Institutes of Health, NIH.
Researchers analyzed blood samples from more than 24,000 people across the country, collected in the first three months of 2020 as part of a long-term study called “All Of Us” that seeks to collect data for 1 million Americans over the years for health studies.
As in the study conducted by the CDC, these researchers looked for antibodies in the blood, proof of coronavirus infection, which can be detected two weeks after infection.
Researchers say nine study participants – five from Illinois and one from Massachusetts, Mississippi, Pennsylvania and Wisconsin – were infected earlier than any case reported by covid in those states.
One of the Illinois state cases has been infected since Christmas, said Keri Althoff, a professor at Bloomberg School of Public Health at Johns Hopkins University and lead author of the study.
Antibodies that neutralize SARS-CoV-2, the virus that causes COVID-19, can be difficult to distinguish from antibodies that fight other coronaviruses, including some that cause the common cold.
Researchers in both the NIH and CDC studies used several types of tests to minimize false-positive results, but some experts say it is still possible that the positive results in 2019 were infections from other coronaviruses rather than the pandemic variant.
“While it is entirely plausible that the virus was introduced into the United States much earlier than usual, this does not necessarily mean that it is strong enough evidence to change the way we think,” said William Hanage, an expert on the dynamics of disease at Harvard University.
NIH researchers have not yet collected data from study participants to see if any of them had traveled outside the United States before becoming infected. But it should be noted that they found that none of the nine participants lived in New York City, Seattle or near them, cities where the first wave of infections was concentrated in the United States.
“The question is, how and where did the virus take root,” said Keri Althoff, a professor at Bloomberg School of Public Health at Johns Hopkins University. The new study, she says, shows that “it has probably taken root in many cities of our country.