[2][3] The infecting coronavirus is an enveloped, positive-sense, single-stranded RNA virus that enters its host cell by binding to the N-acetyl-9-O-acetylneuraminic acid receptor.

[5] Comparison of HCoV-OC43 with the most closely related strain of Betacoronavirus 1 species, bovine coronavirus BCoV, indicated that they had a most recent common ancestor in the late 19th century, with several methods yielding most probable dates around 1890, leading authors to speculate that an introduction of the former strain to the human population might have caused the 1889–1890 pandemic, which at the time was attributed to influenza.

[10] Brüssow, in August 2021, referred to the evidence that OC43 caused the 1889–1890 outbreak as "indirect, albeit weak" and was "conjectural", yet the 1889 epidemic was the best historical record to make predictions about the current COVID-19 path due to the similar "clinical and epidemiological characteristics".

Both viruses can cause severe lower respiratory tract infections, including pneumonia, in infants, the elderly, and immunocompromised individuals such as those undergoing chemotherapy and those with HIV/AIDS.

[18][17][19][20] As OC43 is capable of infecting porcine tissues,[21] it is likely that pigs serve as a zoonotic reservoir for this disease, reinfecting the human population.