Coronavirus: Summer won't stop COVID-19, study suggests

Northern hemisphere countries pinning their hopes on the coming summer to curb the spread of COVID-19 are in for some bad news.

New research out of China suggests the SARS-CoV-2 virus - responsible for almost 100,000 deaths in the past few months - spreads just as easily in hot, humid weather as it does in the cold.

On the flipside, New Zealand's coming winter might not exacerbate the outbreak, should the lockdown fail.

Scientists at Fudan University in Shanghai looked at the weather conditions in 286 cities with reported cases of COVID-19, including temperature, humidity and how much sunlight and UV radiation they received. 

As everyone knows, the flu spreads much more easily in the cold winter months, particularly when the air is dry. But research has shown this also holds true for SARS, a coronavirus very similar to one causing the current pandemic, which killed hundreds of people in the early 2000s. 

"The underlying hypothesis for why warmer seasons tends to decrease the spread of viruses includes higher vitamin D levels, resulting in better immune responses; increased UV radiation; and no school in the summer (when children are clustered together, transmission rates of flu and measles increase)," the new study, published in the European Respiratory Journal on Thursday, says.

"Reports of UV and respiratory diseases have also been studied, and previous studies have shown that high levels of UV exposure can reduce the spread of [SARS]." 

But the Fudan University study found "no significant associations" between the spread of COVID-19 and temperature, UV exposure, humidity or temperature. 

"The result of our analysis suggested that ambient temperature has no significant impact on the transmission ability of SARS-CoV-2," they concluded. "It is premature to count on warmer weather to control COVID-19, and relying on seasonality to curb this pandemic can be a dangerous line of thought."

Instead, SARS-CoV-2 seems to be more like another recent viral respiratory illness called MERS - Middle East Respiratory Syndrome. As its name suggests, MERS is able to thrive in the desert heat. It's much deadlier than COVID-19, with a mortality rate of about 30 percent, but luckily it doesn't spread as easily. 

COVID-19's mortality rate isn't clear yet, but most estimates put it somewhere between 1 and 5 percent. 

The Fudan University team says more research is needed, particularly in regions with temperatures hotter and cooler than found in China. But the towns they looked at ranged from below -15C up to over 20C, "suggesting the robustness of our findings".

New Zealand's average temperatures fall well within this range according to NIWA - the north averaging 16C and the south, 10C. Auckland drops down to an average of 10C in winter, while in Invercargill shivers around 5C.