Seasonal coronaviruses are more prevalent during the winter months, coinciding with influenza and respiratory syncytial virus seasons in temperate climate regions, according to a review recently published in The Journal of Infectious Diseases. Per the researchers, this information is important to build a knowledge base of post-pandemic preparedness.

After the initial pandemic wave of novel SARS-CoV-2 (coronavirus disease 2019; COVID-19), it remains unclear what trajectory of transmission SARS-CoV-2 will take. Similar to influenza and respiratory syncytial viruses, SARS-CoV-2 could recur as a circulating pattern of seasonal outbreaks, which has been observed among other pre-existing human seasonal coronaviruses. Currently, there are 4 known seasonal coronaviruses that circulate in human populations, including NL63, 229E, OC43, and HKU1. However, knowledge on the seasonality of seasonal coronaviruses is lacking. Therefore, this systemic review compared the seasonality of seasonal coronaviruses with the influenza virus and respiratory syncytial virus and modelled monthly activity of seasonal coronaviruses using site-specific weather data.

Studies published between 1990 and 2020 that reported monthly or weekly activity of seasonal coronaviruses NL63, 229E, OC43, or HKU1 were searched for across various databases. In total, seasonality data from 40 sites in 21 countries were included. The number of positive seasonal coronavirus cases by month across years for each site was aggregated, and the annual average percentage was calculated for strength of virus activity. Heat maps were created to display the activity of seasonal coronaviruses, influenza virus, and respiratory syncytial virus for each site to evaluate peak activity for each. Furthermore, meteorological data from each site was extracted from the site’s nearest weather station to model monthly seasonal coronavirus activity.

Results suggested that human seasonal coronaviruses are prevalent in winter months, coinciding with influenza and respiratory syncytial virus season in most temperate sites. High activity of seasonal coronaviruses was observed in winter months in most temperate sites, with the exception of China where seasonal coronavirus activity was noted year-round. More variations in seasonal coronaviruses activity were observed in tropical sites.


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When China was excluded, 53.1% of the annual seasonal coronavirus cases that occurred in temperate sites occurred during influenza seasons, while 49.6% of seasonal coronavirus cases occurred during respiratory syncytial virus season (interquartile range, 34.6-61.9 and 30.2-60.2, respectively). At tropical sites and sites in temperate China, there was less overlap observed between seasonal coronavirus activity and influenza activity (20% of seasonal coronavirus cases during the season) and respiratory syncytial virus activity (29% of seasonal coronavirus cases during the season). In total, 17 studies with more than 100 positive seasonal coronavirus cases were included in the model. Sites with low temperature and high relative humidity were found to be associated with a higher expected proportion of seasonal coronavirus cases, and dew points had a similar relationship with seasonal coronavirus activity.

In terms of limitations, the study could not rule out the possibility of SARS-CoV-2 adapting itself to a distinct circulating season from other sCoVs as a result of competition between viruses, for example. Next, the study did not report seasonality results of sCoV by age, and its findings were based on data collected from mostly temperate sites (88%).  

“Our findings offer clues to the possible post-pandemic circulating season of SARS-CoV-2 and add to the knowledge pool necessary for post-pandemic preparedness for SARS-CoV-2,” the researchers concluded.

Disclosure: One study author declared affiliations with the pharmaceutical industry. Please see the original reference for a full list of authors’ disclosures.

Reference

Li Y Wang X, Nair H. Global seasonality of human seasonal coronaviruses: A clue for post-pandemic circulating season of SARS-CoV-2 virus? [published online July 21, 2020]. J Infect Dis. doi:10.1093/infdis/jiaa436/5874220