The main outbreaks occur during the winter months. This does not mean that Covid-19 will necessarily behave in the same way, but the results of the new study could help fight the pandemic.
Of the seven known coronavirus infections that infect humans, four cause severely seasonal respiratory infections that are transmitted in a similar manner to influenza, according to new work by scientists at the University of Michigan School of Public Health. The authors published an article about this in the Journal of Infectious Diseases.
“Although the seasonal coronaviruses found in Michigan are related to SARS-CoV-2, we do not know if this virus will behave like seasonal coronaviruses,” says Professor Arnold Monto. "Only time will tell if the presence of SARS-CoV-2 in the landscape of respiratory infections will become permanent, continue to circulate restrictedly, as with MERS or SARS, or disappear altogether from the human population."
The researchers note that while coronaviruses in general have long been recognized as causative agents of respiratory diseases, they tend to be mild in their original hosts. However, when animal coronaviruses spread to humans, they can cause serious illness. This is how SARS and MERS started, and, according to all available data to date, it happened with Covid-19.
Monto and colleagues used data from a longitudinal study of respiratory disease in families with children in the Ann Arbor area. Over the past 10 years, from 890 to 1441 people from several hundred households have consistently participated in the study. An ongoing study is currently tracking SARS-CoV-2 penetration into Michigan households.
In 2010, the study began tracking the emergence of four typically mild human coronaviruses (OC43, 229E, HKU1 and NL63). Scientists studied the frequency, seasonality and transmission characteristics of 993 cases of infections caused by these coronaviruses in households.
The attention of doctors required an average of about 30% of cases - 9% in adults and 20% in children. When the year-round surveillance was carried out, most cases of coronavirus were detected between December and April / May, and peaked in January / February. Only 2.5% of cases occurred between June and September. The highest incidence of infection was in children under the age of five.
Of the 993 cases of infection, 260 people became infected from their relatives living with them. The interval between the first patient in the family and cases of transmission between members of this family (serial interval) ranged from 3.2 to 3.6 days; the risk of re-infection ranged from 7.2% to 12.6%, depending on the type. Severe cases were more likely to occur in children under the age of five and older adults (50 and over).
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Monts and colleagues say the coronaviruses studied in Michigan are highly seasonal and, judging by the serial interval and the risk of re-infection, in the studied population have the same transmission potential as the influenza A (H3N2) virus. However, they note that the results do not indicate directly how SARS-CoV-2 will behave.
Among other things, in a separate, still ongoing study, the authors use samples collected before the known time of the onset of the Covid-19 pandemic to understand when SARS-CoV-2 first penetrated local communities in the state. Preliminary results do not indicate that SARS-CoV-2 was present in these locations until March.
Author: Sofia Zhabotinskaya