The world is looking for signs that the arrival of warmer weather in the northern hemisphere could slow the spread of the coronavirus outbreak, which has killed more than 190 000 people and sent the global economy into a tailspin as countries impose lockdowns and restrict travel.
Here’s what we know about seasonal features of disease outbreaks.
Is the new coronavirus “seasonal”?
That’s what some infectious disease experts are hoping. But they cannot be sure because this virus has not been around long enough for scientists to collect the evidence they need.
“All we have to go on is analogies with other diseases that spread in similar ways,” said Paul Hunter, an infectious disease expert at Britain’s University of East Anglia.
What specialists do know is respiratory infections like flu, coughs and the common cold can have seasonal influences that make outbreaks of them easier to predict and contain.
It’s also known that certain environmental conditions can boost transmission of viruses: Cold weather, humidity, and the way people behave during winter can all affect the trajectory of an epidemic.
“We don’t know for this particular virus if it’s seasonal or not, but we do know that there is a seasonality involved for other coronaviruses,” said Leana Wen, an emergency physician and public health professor at George Washington University who formerly served as Baltimore’s Health Commissioner.
What is it about winter that helps respiratory diseases spread?
“The reason why cold weather is presumed to cause spreading of coughs, colds and flu is that cold air causes irritation in the nasal passages and airways, which makes us more susceptible to viral infection,” said Simon Clarke, an expert in cellular microbiology at Britain’s University of Reading.
Winter weather also tends to see people spending more time indoors and clustering together.
Many respiratory infections are spread in droplets that are released when an infected person coughs or sneezes. According to disease experts, when the air is cold and dry, those droplets are more likely to float in the air for longer – travelling further and infecting more people.
United States government researchers have determined that the coronavirus loses potency when temperatures and humidity rise – and especially when it is exposed to sunlight, William Bryan, acting head of the Department of Homeland Security’s Science and Technology Directorate, said on Thursday.
The new coronavirus seems to decay faster in humid environments. In experiments in darkness and low humidity, it took 18 hours for half of the virus particles to lose function on nonporous surfaces like stainless steel, the U.S. research found.
In high humidity, that half-life – the time it takes for half the virus particles to become inactivated and no longer infectious – dropped to six hours. In high humidity and sunlight, the half-life dropped to two minutes.
“We know viruses are affected by the environment they are in, and many viruses do not survive in places with high temperature or if ultraviolet radiation exposure is high,” said Amesh Adalja, a senior scholar at the Johns Hopkins University Centre for Health Security and a spokesman for the Infectious Diseases Society of America.
But Adalja cautioned that while summer conditions may impair the ability of the virus to survive on surfaces, that did not mean it couldn’t be transmitted from person to person.
So will warmer weather help bring COVID-19 under control?
Hunter said it was likely “that the disease will decline substantially during the summer months in the northern hemisphere”.
“Whether it comes back again is a moot question,” he added. “It would not surprise me if it largely disappeared in summer only to reappear again in the winter.”
In general, however, the new virus “likely will continue” to spread given that so many people have no immunity, Adalja said. (Reuters)
