New studies from the National Institutes of Health (NIH) and the Centers for Disease Control and Prevention (CDC) have concluded SARS-CoV-2, the novel coronavirus responsible for COVID-19, was likely circulating around the United States for several weeks prior to the first officially reported case in late January 2020.
The current timeline for the beginning of the COVID-19 pandemic goes back to Wuhan, China, in late 2019. On the eve of 2020 the World Health Organization was notified by China of an ongoing and unexplained viral pneumonia outbreak. The exact nature of those early cases is still unclear, but it is generally believed the first infections of this novel coronavirus occurred in, or around, Wuhan across late November and early December in 2019.
The first officially reported case in the US was on January 19th in a traveler recently returned from China. However, a pair of new studies looking for SARS-CoV-2 antibodies in blood samples gathered as early as December 2019 are suggesting the virus may have been circulating the country for weeks, if not months, prior to that first official case.
The first study, led by the National Institutes of Health, looked at blood samples taken as part of an ongoing long-term observational study called All of Us. Researchers tested samples gathered from 24,000 subjects between January and March in 2020 spanning all 50 states.
Two different serology platforms were used to test the blood samples for SARS-CoV-2 antibodies, and the samples needed positive results from both platforms to be considered a confirmed COVID-19 case. Nine positive cases were ultimately detected in the study – coming from Illinois, Massachusetts, Mississippi, Pennsylvania and Wisconsin.
The two earliest cases detected in the study were from specimens collected in Illinois on January 7th and Massachusetts on January 8th. As positive antibodies usually develop at least two weeks after initial infection the researchers hypothesize this means both cases were infected no later than Christmas Eve in 2019.
The second study, this time led by researchers from the CDC, used a similar methodology to analyze more than 7,000 samples of blood from routine Red Cross donations taken between the 13th of December 2019 and the 17th of January 2020. In total, 106 samples tested positive to SARS-CoV-2 antibodies, with the earliest detections concentrated in California, Oregon, and Washington around the 13th of December.
While there has been debate over the past year concerning how accurate these serology antibody tests are, the technology has certainly improved over time and researchers are confident they now have excellent sensitivity and specificity. Both new studies also performed additional, more specific, testing on the positive samples to confidently conclude their overall findings as robust, even in the instance of some false positives.
“Antibody testing of blood samples helps us better understand the spread of SARS-CoV-2 in the U.S. in the early days of the U.S. epidemic, when testing was restricted and public health officials could not see that the virus had already spread outside of recognized initial points of entry,” explains Keri Althoff, lead author on the NIH study. “This study also demonstrates the importance of using multiple serology platforms, as recommended by the CDC.”
Exactly how long SARS-CoV-2 could have been circulating globally before it was officially detected is a question hotly debated amongst scientists. A thorough modeling study published a couple of months ago argued it was certainly possible the novel coronavirus was circulating in China for several weeks before its official detection. Joel Wertheim, senior author on that modeling study, said in March he finds it hard to believe the virus was widely dispersed outside of China before December 2019.
“… it’s hard to reconcile these low levels of virus in China with claims of infections in Europe and the US at the same time,” said Wertheim. “I am quite skeptical of claims of COVID-19 outside China at that time.”
Wertheim’s computer modeling found in more than 70 percent of epidemic simulations the virus infected very few people before dying out. He demonstrated in a majority of scenarios SARS-CoV-2 infection would not lead to the kind of widespread pandemic that we ultimately experienced. This means it is possible several chains of transmission appeared in the United States earlier than January 2020, but they all quickly fizzed out.
Natalie Thornburg, principle investigator on the new CDC study agrees that although her team's research did point to cases occurring earlier than previously assumed, the spread of the novel coronavirus didn’t really take off until February 2020.
"There was probably very rare and sporadic cases here earlier than we were aware of,” says Thornburg. “But it was not widespread and didn't become widespread until late February.”
The NIH and CDC studies were published in the journal Clinical Infectious Diseases.
Source: NIH
