Tests of blood donation samples by the US Centers for Disease Control and Prevention show that antibodies against SARS-CoV-2 were already present in human bodies in the US as early as mid-December last year.

A new study that analyzed blood donations from December 2019 to early January helped show that the coronavirus infected people in the US earlier than previously thought. (File photo: agencies)

The study published in the journal Clinical Infectious Diseases on Monday concluded, “SARS-CoV-2 infections may have been present in the US in December 2019, earlier than previously recognized.”

CDC researchers tested a total of 7,389 blood samples collected from donors by the American Red Cross in nine US states between Dec. 13, 2019 and Jan. 17, 2020.

The study identified 106 samples with antibodies, including 39 collected between December 13 to December 16, in California, Oregon and Washington state.

Researchers believe the study indicates that there were isolated infections in the western part of the US in mid-December last year.

Antibodies were also found in samples between December 30 to January 17 in other states including Massachusetts, Michigan, and Wisconsin, all before January 19 when the first US case emerged.

(Compiled by Han Xiaomeng)