Fatality rates from Covid-19 are lower when temperatures are warmer, according to a study published by the City University of Hong Kong.
The team, led by Sean Yuan, an assistant professor in biomedical sciences, examined data collected in eight European countries between February and July 2020, during the initial wave of the pandemic.
They found that warmer temperatures are associated with lower death rates, especially when they are above 15 degrees Celsius.
But the study noted that the relative humidity and different stages of infection also play a part in affecting the risk of mortality among coronavirus patients.
During the early stages of infection, temperatures above 20 degrees Celsius, alongside dryer conditions, could reduce the risk of death, the team said.
On the other hand, patients who have shown symptoms for a few days are likely to have a lower fatality risk in more humid weather.
"For instance, high relative humidity (89 percent) during the first few days after symptoms appear can reduce the fatality rate by 31 percent, compared to 62 percent relative humidity," the report said.
Separately, the research team discovered that environmental conditions might affect not only the initial viral load of a person when exposed to the virus, but also how their immune system responds after the onset of symptoms.
"At a later time period when symptoms appear, so that time is the time [for] innate immune response to activate," Yuan explained to RTHK.
"Some animal studies show that there's a kind of innate immunity system, also called [the] mucosa barrier, when animals inhale humid air, then [the] mucosa barrier will help to remove pathogen to outside more efficiently," he added.
The team said it believes the findings point to a way to reduce Covid fatalities at a time when Hong Kong is experiencing an unprecedented surge in deaths among Covid patients, most of them elderly people but also some young children.
“The weather in Hong Kong has been extreme recently. In addition to symptoms such as shortness of breath, fever and sore throat, patients are affected by cold weather," Yuan said.
The professor recommended that patients be kept warm, and said after symptoms appear, infected individuals should inhale more warm and humid air, while keeping a face mask on.
That also goes for sealed-off housing blocks and isolation facilities.
"[The government] should think about, there are many potential cases inside, so how to make sure in winter those buildings they can maintain a much healthier environment for people inside," Yuan said.
He added that more studies ought to be conducted to determine the best indoor environmental conditions for patients who are isolating at home or in hospital.