A new study suggests that COVID-19 may have been introduced in the United States earlier than the first reported cases of the virus in mid-January.
“The findings of this report suggest that SARS-CoV-2 infections may have been present in the U.S. in December 2019, earlier than previously recognized,” the study, which was published in the journal of Clinical Infectious Diseases Monday, said.
The scientists gathered blood donations collected by the American Red Cross from Dec. 13, 2019, to Jan. 17, 2020, from donors in California, Connecticut, Iowa, Massachusetts, Michigan, Oregon, Rhode Island, Washington, and Wisconsin, testing the samples for COVID-19 antibodies.
The scientists used “serologic testing” to analyze the samples, which had “been previously used to estimate the introduction of viral infections into the population, including for HIV.”
“Of the 7,389 samples, 106 were reactive,” the study’s authors wrote. “Of these 106 specimens, 90 were available for further testing.”
The scientists found that 84 of the 90 samples had “neutralizing activity” that suggested “the presence of anti-SARS-CoV-2-reactive antibodies.”
“Donations with reactivity occurred in all nine states,” the authors added.
The authors note that “some reports have suggested the introduction” of the virus into the U.S. may have “occurred earlier than initially recognized,” but that “widespread transmission was not likely until late February.”
The first cases of COVID-19 were identified in the U.S. on Jan. 19, 2020.
The study’s results largely echo those of a similar study in Italy, which found that COVID-19 antibodies were already circulating in the country as early as September 2019.
That study analyzed blood samples from 959 asymptomatic patients that were enrolled in a lung cancer trial in Italy, with 14% of the samples showing “specific antibodies” as early as September 2019. By the second week of February 2020, close to 30% of samples screened positive for COVID-19 antibodies.
“This study shows an unexpected very early circulation of SARS-CoV-2 among asymptomatic individuals in Italy several months before the first patient was identified, and clarified the onset and spread of the coronavirus disease 2019 (COVID-19) pandemic,” the study’s abstract reads. “Finding SARS-CoV-2 antibodies in asymptomatic people before the COVID-19 outbreak in Italy may reshape the history of pandemic.”
Scientists from the more recent study in the U.S. note that the research has limitations, including the “detection of reactive antibodies” that could potentially have cross-reactivity with other coronaviruses found more frequently in common colds.
A September study found that many school-age children already had antibodies from infections with other coronaviruses that could block the SARS-CoV-2 strain causing the pandemic.
The study found that about 5% of adults and 43% of children already possessed antibodies that block COVID-19 transmission. The study also pointed out that while antibodies eventually go away, T cells can remain in the body much longer and be activated to help fight new coronavirus infections.
Those results mimic a Harvard Medical School study, which showed many people already had preexisting antibodies from coronavirus colds. The results could explain why children are less likely than adults to become infected with or become severely ill from COVID-19, as children catch up to a dozen colds per year while adults typically only catch two.
The study notes that further research is needed to “further corroborate the present findings, which suggest the presence of specific antibodies to SARS-CoV-2 in the U.S. as early as mid-December 2019.”
“CDC is continuing to work with federal and non-governmental partners to conduct ongoing surveillance using blood donations and clinical laboratory samples for SARS-CoV-2 infection in multiple sites across the U.S.,” the authors wrote. “Understanding the dynamics of SARS-CoV-2 pandemic from early introduction throughout further progression will advance understanding of the epidemiology of this novel virus and inform allocation of resources and public health prevention interventions to mitigate morbidity and mortality associated with COVID-19.”
