SARS-CoV-2, the virus behind COVID-19, will likely settle into a seasonable rhythm like influenza, becoming most active during the colder months in northern climes and subsiding in summer, according to a study.

As COVID-19 becomes endemic, infecting populations in wave after wave annually, scientists are trying to determine whether the timing of these surges will ever be predictable.

"Having some idea of when we'll have surges in the future is important for public health policy and decision-making," said Jeffrey Townsend, Professor of Biostatistics and Ecology and Evolutionary Biology, at Yale University in the US. 

"Late fall, winter, and early spring are the highest-risk times for surges of infection," he added. 

The study, published in the journal mBio, can help clinics and hospitals prepare for large numbers of COVID-19 patients. 

This foreknowledge is especially important because other respiratory viruses like influenza and respiratory syncytial virus (RSV) may be active around the same time, further burdening healthcare systems. 

The researchers predicted future seasonality -- when during the year SARS-CoV-2 will most actively circulate -- using historic infection data from coronaviruses with known seasonal patterns that are often attributed to causing colds.

In the study, the team analysed monthly infection data of common-cold coronaviruses reported in previous studies conducted in locations in Europe, East Asia, and North America. 

Collectively, these studies had amassed viral samples from thousands of people between 1985 and 2020. 

Using statistical methods, the researchers estimated that SARS-CoV-2 will tend to surge in colder months, at least in the temperate places of the Northern Hemisphere they studied. 

However, the exact timing will vary by location. A key caveat: the results apply once COVID-19 becomes an endemic disease. 

That hasn't happened yet, but most experts agree it's coming, Townsend said. What will endemicity look like? "It's steady in the population -- our immune systems have been exposed to it a bunch of times, we're trucking along without interventions, and it's spreading the same way every year," Townsend said. 

"How many years it will be until we reach that point is unclear. Maybe we're almost there, or maybe it'll be another 10 years."