By Stan Deresinski, MD, FACP, FIDSA

Clinical Professor of Medicine, Stanford University

Dr. Deresinski reports no financial relationships relevant to this field of study.

SYNOPSIS: In temperate regions other than China, human seasonal coronaviruses circulate most heavily during the winter months, overlapping with influenza and respiratory syncytial virus — and this may be the eventual pattern for SARS-CoV-2.

SOURCE: Li Y, Wang X, Nair H. Global seasonality of human seasonal coronaviruses: A clue for post-pandemic circulating season of SARS-CoV-2 virus? J Infect Dis 2020; Jul 21:jiaa436. doi:10.1093/infdis/jiaa436. [Online ahead of print].

Speculation regarding the behavior of COVID-19 after the pandemic wave is brought into a semblance of stability continues and is of great importance for the future of this disease and the response to it. It is unlikely that SARS-CoV-2 will disappear from the face of the earth, thus leaving two major possibilities: ongoing year-round transmission with occasional regional spikes or seasonal transmission as has occurred after the appearance of influenza pandemic strains. One source of information that potentially can inform the debate on this issue is the behavior of the four endemic coronaviruses that primarily cause symptoms of a common cold.

Li and colleagues performed a systematic review to assess the global seasonality of existing seasonal human coronavirus infections (sCoV). They found that in temperate regions other than China, the winter months accounted for high sCoV activity, as measured by the annual average percentage. In China, sCoV activity occurred year-round.

In examining temperate regions (with the exclusion of China), researchers found that 53.1% of sCoV cases occurred during the influenza season and 49.6% occurred during the respiratory syncytial virus season. Lesser overlap occurred in tropical regions, as well as in temperate China (20% and 29% overlap, respectively). An examination of meteorological factors found that higher proportions of sCoV cases were associated with periods of low temperature and higher relative humidity.

COMMENTARY

A previous modeling study concluded that if, as has been demonstrated with sCoV, immunity to SARS-CoV-2 is not long-lasting, it will begin its circulation pattern beginning in 2021 or 2022 and will synchronize with circulation of the four human sCoV.¹ Thus, as also indicated by the empiric evidence discussed above, SARS-CoV-2 will cocirculate not only with sCoV but with influenza and respiratory virus infections. Since symptoms of infections due to these viruses overlap, clinical diagnoses cannot be relied on. Accurate, rapid-turnaround, and preferably point-of-care tests will be needed.

Get ready for a long, complicated, and never-ending ride.

REFERENCE

1. Kissler SM, Tedijanto C, Goldstein E, et al. Projecting the transmission dynamics of SARS-CoV-2 through the postpandemic period. Science 2020;368:860-868.