Is COVID-19 a seasonal disease? 

Last month, the results of a COVID-19 study in New South Wales, Australia suggested the disease spreads faster in periods of lower humidity during winter. Several weeks later, after a fresh outbreak in neighbouring Victoria that followed the Southern Hemisphere’s change in seasons, authorities decided to close the border between the two states for the first time since the Spanish flu pandemic a century earlier.

The scientific community has yet to determine the exact relationship between seasonal change and the spread of COVID-19 in different parts of the world. The executive director of the World Health Organization’s Health Emergencies Program said last month it was unclear how the arrival of winter in the Southern Hemisphere would affect the situation there. Still, some experts say it’s reasonable to expect at least some seasonal fluctuation. So, even as Australia’s response to the pandemic has largely been deemed a success, challenges were anticipated as winter loomed.

What we do know for certain about the coronavirus at this point can seem relatively limited: it’s constantly mutating, appears to be increasingly infectious, and may cause a painful swelling dubbed “COVID toe,” for example. Yet our level of understanding increases daily. According to the search engine PubMed, more than 19,000 academic papers mentioning “coronavirus” have already been published so far in 2020, compared to 750 in all of last year. The precise impact of changing seasons is just another knowledge area to be filled in.

That hasn’t stopped speculation about what lies ahead for Northern Hemisphere when winter arrives there – particularly in places like the US, which have still largely failed to stem the initial spread of the pandemic.

Another Southern Hemisphere data point can be found in South Africa. Earlier this month, that country reported its highest daily total of confirmed COVID-19 cases to date, about two weeks after the winter solstice.

Experts have warned winter conditions could hurt South Africa’s efforts to curb the coronavirus not least because more people may stay indoors in places heated by wood and coal stoves, which emit particulate matter that can further the spread.

It has been widely noted that the Spanish flu pandemic surged during the colder months of 1918 and 1919, which some have seen as an indication of what’s in store with COVID-19. It is also yet another reason experts say comprehensive testing and contact tracing will be essential until a vaccine can be developed.

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