Identified Human Coronaviruses Follow Similar Seasonal Infection Patterns

According to a paper published in The Journal of Infectious Diseases, 4 human coronaviruses (HCoV) that were studied have similar seasonal peaks and patterns and a majority of cases are categorized as mild for all age groups.

Investigators from University of Michigan School of Public Health utilized data from the Household Influenza Vaccine Evaluation (HIVE) study in order to report the occurrence of the 4 HCoV types over an 8-year period. Those types are OC43, 229E, HKU1, and NL63. Part of the HIVE study reported on acute respiratory infections (ARIs) between 2010 and 2018 and followed between 890 and 1,441 individuals who were contacted weekly to report any ARI symptoms. The investigators ultimately identified 993 HCoV infections over the course of those 8 years.

HIVE participants were asked to report onset of 2 or more ARI symptoms for anyone in their household (commonly categorized as households with 4 or more members, at least 2 of whom were under 18 years of age) via phone calls and email contacts with investigators. These symptoms included cough, fever, nasal congestion, chills, headache, body aches, and sore throat.

For each of the listed seasons, the investigators reported counts of the 4 HCoVs as follows:

• 2010-11 season: 152 cases
• 2011-12: 59 cases
• 2012-13: 200 cases
• 2013-14: 105 cases
• 2014-15: 113 cases
• 2015-16: 109 cases
• 2016-17: 112 cases
• 2017-18: 143 cases

In the first 5 of the 8 years, there was no surveillance conducted from June to September, the investigators noted. However, in years where year-round surveillance was implemented, only 2.5% of the total 364 HCoV cases occurred from June to September. Throughout the study period, the investigators determined that HCoV cases increased in December, peaked in either January or February, and began to decrease by March. Each of the 4 HCoV types was relatively similar in their peak and valley, the study authors noted, called it a “striking” similarity.

For 3 of the HCoVs, infection rates were highest in young children and dropped off as age increased; however, the study authors found an exception for 229E. With that HCoV, incidence per 100 person-years was relatively low and did not vary by age, but the incidence was highest among children under the age of 5 years.

Mild illnesses with HCoV were characterized by cough and fatigue, and moderate illnesses were additionally likely to have fever or miss school or work. Those with severe illness typically had symptoms such as wheezing, dyspnea, or sought care for their illness. Almost 3 in 5 illnesses were categorized as mild (59%), the study authors noted, and moderate and severe illness made up 31% and 10% of HCoV infections, respectively. HCoV illness in children under 5 years and in adults over 50 years was most likely to be classified as severe, the study authors added.

The investigators noted that of 993 HCoV identified, 260 occurred within 14 days of exposure to a household contact infected with the same type of HCoV. In the case of 229E, adults aged 18 to 49 were responsible for nearly half of the household transmissions, but in the other 3 HCoVs, transmission rates were similar for all age groups (except children under 4).

“The regular appearance of all types of coronaviruses in the same months with minimal circulation in the summer was a clear finding of this study,” the study authors concluded. “Unlike the influenza viruses, which peak at different times during the colder season from year to year, and even the rhinoviruses, which are most common in the autumn and spring but are present year round, the coronaviruses are sharply seasonal with little spread after May until November or December."