4 Known Human Coronaviruses Are Highly Seasonal, Study Finds

As epidemiologists work to track the novel coronavirus and predict its next moves, a new study from the University of Michigan found that other human coronaviruses behave in a highly seasonal, highly predictable manner.

The investigators of the study, which was published in The Journal of Infectious Diseases, examined the 7 coronaviruses known to infect humans, focusing on the 4 that cause severe respiratory infections.

All 4 of those were found to be highly seasonal. While the findings don’t have direct bearing on whether or not the novel SARS-CoV-2 is likewise affected by the changing of seasons, the investigators say they hope their study will provide valuable context.

“Even though the seasonal coronaviruses found in Michigan are related to SARS-CoV-2, we do not know whether that virus will behave like the seasonal coronaviruses," wrote Arnold Monto, MD, a professor of epidemiology at the university’s school of public health, and colleagues.

The findings are based on the university’s Household Influenza Vaccine Evaluation study, comprised of volunteer families (adults and children) who received care from the University of Michigan Health Care System.

For the past decade, the study has tracked between 890 and 1441 individuals annually, checking in with them weekly to inquire about acute respiratory infections. Specimens were collected from patients with infections, and the specimens were tested for the 4 human coronaviruses that cause respiratory infections: types OC43, 229E, HKU1, and NL63.

Altogether 993 human coronavirus infections were identified. Type OC43 was the most commonly found within the study group; type 229E was the least common.

Monto and colleagues report that all 4 coronaviruses appeared only in the winter and early spring.

“Combined over the 8 years, the number of identifications for each virus increased in December, peaked in January or February, and began to decrease in March,” Monto and colleagues wrote.

“The seasonal similarity between the 4 types is striking, with only the peak aggregate month differing between January and February.”

The investigators noted that the coronaviruses’ seasonality was more predictable than that of influenza, since flu season can peak at different times of the winter months from year to year.

Monto and colleagues note that the 4 coronaviruses included in the study have been around for decades; so long that investigators don’t know when or how they first appeared in humans.

However, that doesn’t necessarily mean SARS-CoV-2 will act in the same way. They note that Severe Acute Respiratory Syndrome (SARS), which was identified in 2002, and Middle East Respiratory Syndrome, identified in 2012, both behave somewhat differently.

“Only time will tell if SARS-CoV-2 will become a continuing presence in the seasonal human coronavirus landscape, continue with limited circulation as with MERS, or like SARS, disappear from humans altogether,” they wrote.

In the meantime, Monto’s team continues to research the virus. In a separate study, the team has been looking at samples taken before the SARS-CoV-2 epidemic to look for evidence of community transmission.

To date, the team says they have found no evidence of the novel virus being present in the community prior to March of this year.