Michigan Study Finds Common Human Coronaviruses Seasonal, Like Flu

NIAID Now | April 13, 2020

This scanning electron microscope image shows SARS-CoV-2 (yellow), the virus that causes COVID-19, emerging from the surface of infected cells (pink) grown in the lab. SARS-CoV-2 is similar to the viruses investigated in the current study.

Credit: NIAID

The four most common human coronaviruses circulate seasonally, primarily infect children under age 5 and mainly cause mild disease, according to a new University of Michigan study in The Journal of Infectious Diseases. The scientists, from UM’s School of Public Health, also determined that the viruses transmit similarly to seasonal influenza A(H3N2) virus.

The group is hoping its eight-year household infection study of the little-known coronaviruses can help colleagues around the world illuminate characteristics about the very different pandemic coronavirus SARS-CoV-2, which causes COVID-19. Older adults appear to be at higher risk of complications from infection with SARS-CoV-2 and COVID-19 is believed to be more severe to manage clinically than influenza, but researchers are unsure if and how it will continue to circulate.

With funding from the National Institute of Allergy and Infectious Diseases, the UM scientists from 2010 to 2018 used specific monitoring guidelines to track respiratory infections. Between roughly 900 and 1,400 residents with children participated each year in the Ann Arbor area, accounting for roughly 300 households annually. They designed the project primarily to evaluate influenza virus, but they also tracked human coronaviruses OC43, 229E, HKU1 and NL63. All four coronaviruses are widely considered to cause mild respiratory illnesses. Researchers have known about OC43 and 229E for decades, and HKU1 and NL63 were more recently identified as part of SARS-CoV-1 research projects. Severe acute respiratory syndrome coronavirus disease (SARS-CoV) emerged in 2002 but disappeared in 2004 thanks to standard infection control measures. The first SARS virus to emerge surprised scientists because it was the first human coronavirus to show human-to-human transmission with severe disease. 

The UM study identified 993 human coronavirus infections during the eight years and detected a seasonal pattern of infection. Outbreaks typically began in December, peaked in January and February, decreased in March and ended by May. Very few coronavirus cases occurred from June through September.

Of the 993 infections, 260 were secondary cases, meaning those acquired from an infected person in the household. The secondary cases occurred about 3 to 4 days after the original case.

Overall, 9% of adult and 20% of child cases led to medical consultation. When rating cases based on symptoms and illness outcomes, 59% were deemed mild (cough and fatigue), 31% moderate (fever and missed school or work), and 10% severe (wheezing, labored breathing, likely to seek care).

Virus 229E was most likely to produce severe disease compared to the other three, but also was the least commonly diagnosed. NL63 was least likely to produce severe disease, but also was more commonly diagnosed. In most years when cases spiked for one of the viruses, cases of that virus waned the following year.

The researchers plan to use this ongoing cohort to study how SARS-CoV-2 behaves in Michigan households. They also expect to study the role of prior antibody presence to the common coronaviruses in protecting against subsequent confirmed infection with one of the viruses.


A. Monto, et al. Coronavirus occurrence and transmission over 8 years in the HIVE cohort of households in Michigan. The Journal of Infectious Diseases. DOI: https://doi.org/10.1093/infdis/jiaa161

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