Health experts expect cooler weather conditions in the winter to trigger a more intense transmission of the Covid-19 infection, warning it is “very likely” the illness will show a similar seasonal pattern to other coronaviruses.
The warning comes as countries in the Southern Hemisphere brace for a potential uptick in Covid-19 cases during the winter months.
To date, more than 6.1 million people have contracted the coronavirus across the globe, with 372,099 deaths, according to data compiled by Johns Hopkins University.
The pandemic has brought large swathes of the world economy to a halt in a matter of months, with political leaders imposing stringent measures on the daily lives of billions of people.
President Donald Trump had previously suggested that the novel coronavirus SARS-CoV-2 and the disease it causes, Covid-19, would “miraculously” go away on its own during warmer summer weather in the Northern Hemisphere.
But, Marc Lipsitch, professor of epidemiology at Harvard has said that while he anticipates a slight decline in the contagiousness of the coronavirus in warmer, wetter weather, “it is not reasonable to expect these declines alone to slow transmission to make a big dent.”
In winter, however, Lispitch said he did have reason to believe Covid-19 “may transmit somewhat more efficiently” when compared to summer.
The size of the change was expected to be modest and Lispitch conceded he did not yet know the mechanisms responsible. Nonetheless, colder weather, dryer air both indoors and out, and the way people behave during winter were all cited as factors likely to impact the trajectory of the coronavirus.
“I think it is a pertinent point,” Simon Thornley, senior lecturer of epidemiology and biostatistics researcher at Auckland University in New Zealand, told CNBC via telephone.
It is “very likely” Covid-19 will show a similar seasonal pattern to other common human coronaviruses, he continued, citing types including HKU1, 229E and OC43.
These coronaviruses all cause influenza-like illness, Thornley said, “or at least they have a higher seasonal peak in the winter.”
What is it about winter weather?
In winter, people tend to spend more time indoors clustered together, with less ventilation and less personal space than in summer.
Respiratory infections, such as coronaviruses, are spread by droplets that are released when a person coughs or sneezes. And, health experts say colder and drier conditions in winter strongly affects the transmission of flu-like illnesses.
“It’s not just in Game of Thrones that winter is always coming — it is also true in every health service,” Chris Whitty, England’s chief medical officer, said during an online Gresham College lecture in late April.
He warned a second wave of Covid-19 cases could be “more severe” than the first, adding that winter was “always worse than summer” for respiratory viruses, and there was a higher likelihood of transmission during the colder months.
Why might New Zealand not need to worry?
“If you have a widespread circulating virus, I think it is a reasonable assumption that transmission will become more intense in winter,” Michael Baker, an epidemiologist at the University of Otago in Wellington, New Zealand told CNBC via telephone.
Baker said coronaviruses, and indeed all respiratory viruses, were “highly seasonal” in temperate countries like much of Europe and North America, as they are in New Zealand and Australia.
However, he suggested there might soon be some good news for New Zealand on this subject, before adding: “We hopefully won’t have to worry about winter because there won’t be any virus here.”
New Zealand, which will enter the winter season from June 21, has been widely praised for its response to the coronavirus pandemic.
To date, Zealand has recorded 1,504 cases of the virus, with 22 deaths nationwide.
The country of roughly 4.8 million has successfully stopped local transmission and is taking steps to try to eliminate the virus from its territory.
On Wednesday, New Zealand’s director-general of health told reporters at the Covid-19 press briefing that the country had discharged its last remaining patient from hospital.
‘The pandemic we should not have had’
The U.S. has recorded by far the highest number of Covid-19 cases and fatalities worldwide.
As of Wednesday evening, it had reported more than 100,000 deaths, significantly higher than any other country.
Brazil has recorded the second-highest number of Covid-19 cases to date, with 514,849 reported infections, while as many as 10 other countries have also recorded more than 100,000 cases of the virus as it continues to spread across the globe.
“I just feel quite sad that we haven’t, in the year 2020, been able to manage this pandemic — the pandemic we should not have had,” University of Otago’s Baker said.
“We could have greatly reduced the impact of this pandemic and I’m quite shocked in the modern age that we have allowed this to happen globally,” he added.