Longer hours of sunlight linked to higher Covid-19 incidence: Study

Toronto, June 10  Scientists have found that while greater heat and humidity can slow the spread of Covid-19, longer hours of sunlight is associated with a higher incidence of the disease.

The studies, published journal Geographical Analysis, inform the widespread scientific debate over how seasonal changes, specifically warmer weather, might shape the spread of Covid-19.

While research has shown that pathogens such as influenza and SARS thrive in lower temperatures and humidity, little is known about SARS-CoV2, the agent that causes COVID-19.

“There is a lot of pressure to reopen the economy, and many people want to know if it will be safer to do so in the summer months,” said study lead author Antonio Paez, Professor at McMaster University in Canada.

“Restrictions in movement, which have begun to ease around the world, hinge in part on how SARS-CoV2 will be affected by a change in season,” he said.

For the results, the researcher team investigated climate factors in the spread of Covid-19 in several provinces in Spain, one of the countries hardest hit by the pandemic.

They combined and analysed data on reported cases of the disease and meteorological information over a period of 30 days that began immediately before a state-of-emergency was declared.

At higher levels of heat and humidity, researchers found that for every percentage increase, there was a three per cent decline in the incidence of Covid-19, possibly because warmer temperatures curtail the viability of the virus.

The opposite was true for hours of sunshine: more sun meant greater spread.

The researchers speculate the increase may be related to human behaviour since compliance with lockdown measures breaks down in sunnier days.

They were also surprised to find rates of transmission dropped among more dense populations and in areas with more older adults, suggesting those populations regard themselves as being at greater risk, and so are more likely to adhere to lockdown guidance.

While older adults are more vulnerable to the disease, researchers believe they are less likely overall to contribute to the spread of the disease because they are more apt to be isolated from others because of health or mobility issues.

The researchers stressed that models such as this one show that contagion of COVID-19 declines as a lockdown progresses, possibly to the vanishing point – an argument for maintaining discipline despite the approach of pleasant weather.

Earlier this month, another study published in the journal Transboundary and Emerging Diseases, revealed that Covid-19 could be a seasonal illness with a higher risk in winter.

The study found an association between lower humidity and an increase in locally acquired positive cases.