Summer could slow coronavirus, but it is unlikely to stop it


The arrival of warmer weather in the northern hemisphere raises the question of whether summer could slow the spread of the coronavirus epidemic. Here’s what science says.While warmer weather generally ends the annual flu season in temperate zones, the climate alone has not prevented the COVID-19 pandemic from sweeping any part of the globe. In fact, outbreaks in hot, sunny Brazil and Egypt are increasing.

Yet recent data on how sunlight, humidity and outside breezes affect the virus give reason to be optimistic that summer could slow the spread.


The virus has not been around long enough to be certain.

Respiratory infections like the flu and the common cold follow seasonal patterns in temperate regions. Environmental conditions, including cold weather, low indoor humidity, and spending more time indoors, can all accelerate the spread of an epidemic.

Actual evidence of the effect of weather on the new virus is mixed. A study of 221 Chinese cities found that temperature, humidity and daylight did not affect the speed of propagation.

Two other studies have found an effect, including a review of new infections in 47 countries that have linked higher temperatures to slower transmission in places like the Philippines, Australia and Brazil. “The northern hemisphere could see a drop in new COVID-19 cases in the summer and a resurgence in the winter,” concluded the authors of another study from 117 countries, which found that with each 1 degree increase in latitude distance from the equator was associated with a 2.6% decrease in records.


“The reason why cold is supposed to cause the spread of coughs, colds and flu is that cold air causes irritation of the nasal and respiratory tracts, which makes us more susceptible to viral infections”, said Simon Clarke, expert in cell microbiology at British University of Reading.

Winter tends to encourage people to spend more time indoors, although air conditioning can also bring people indoors in summer.

In the laboratory, when temperatures and humidity rise, particles of coronaviruses on surfaces lose their ability to infect people more quickly – and they are inactivated particularly quickly when exposed to the sun, researchers from the US government have discovered. .

Experts say it’s always a good idea for people to wash their hands frequently, practice social distancing, and wear a mask. Although virus particles coughed or exhaled by an infected person disperse faster outside, one study found that a light breeze could carry saliva droplets up to 6 meters (19.69 feet).


Vitamin D: Researchers are studying whether vitamin D levels that regulate immunity in people’s blood affect their vulnerability to infection with the new coronavirus or their condition. The majority of vitamin D in the body comes from the skin’s exposure to the sun.

Pollen: A study in the Netherlands of all “flu-like” diseases, including COVID-19, in recent years concludes that pollen concentrations are a better predictor of sunlight disease trends than sunlight. Pollen clouds act like air filters, catch virus particles, and pollen activates immune responses, even in people without overt allergies.

The study found that flu-like illness started to drop when air pollen reached 610 grains per cubic meter, a typical level from early spring to October in most mid-latitudes. (Report by Kate Kelland in London, Manas Mishra in Bengaluru and Christine Soares in New York, edited by Peter Henderson and Matthew Lewis)


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