Researchers predict COVID-19 will eventually become seasonal virus

The novel coronavirus (COVID-19), the illness caused by the SARS-CoV-2 virus, will likely become seasonal in countries with temperate climates, but only when herd immunity is attained, according to new research published in Frontiers in Public Health. Until that time, COVID-19 will continue to circulate across the seasons, the researchers said.

Many respiratory viruses follow seasonal patterns, especially in temperate regions. For instance, influenza and several types of coronaviruses that cause the common cold are known to peak in winter in temperate regions but circulate year-round in tropical regions.

For the study, the authors reviewed these seasonal viruses, examining the viral and host factors that control their seasonality as well as the latest knowledge on the stability and transmission of SARS-CoV-2. The researchers explained that virus survival in the air and on surfaces, people's susceptibility to infections and human behaviors, such as indoor crowding, differ across the seasons due to changes in temperature and humidity. These factors influence transmission of respiratory viruses at different times of the year.

However, in comparison to other respiratory viruses such as the flu, COVID-19 has a higher rate of transmission, at least partly due to circulation in a largely immunologically naïve population, the researchers said. This means that unlike the flu and other respiratory viruses, the factors governing seasonality of viruses cannot yet halt the spread of COVID-19 in the summer months. However, once herd immunity is attained through natural infections and vaccinations, the researchers said the rate of transmission should drop substantially, making the virus more susceptible to seasonal factors.

Such seasonality has been reported for other coronaviruses, including those that emerged more recently such as NL63 and HKU1, which follow the same circulation pattern as influenza.

These conclusions highlight the importance of public health measures needed to control the virus, researchers said.

"COVID-19 is here to stay and it will continue to cause outbreaks year-round until herd immunity is achieved,” said Hassan Zaraket, PhD, senior author of the study from the American University of Beirut in Lebanon. “Therefore, the public will need to learn to live with it and continue practicing the best prevention measures, including wearing of masks, physical distancing, hand hygiene, and avoidance of gatherings.”

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