Now that two years have passed since the new coronavirus attacked Planet Earth, can we determine in which of the seasons it has spread most? Do climate and weather factors make the infection more or less severe?
It has become evident in the past period of time that the number of COVID-19 cases and infections arise as temperature and humidity levels fall; i.e. in winters. However, we notice that in many countries, such as the USA, infection levels have risen in the summer when temperature and humidity levels rise! Does this indicate that the coronavirus infection is seasonal?
Scientists indicate that respiratory system viruses actually tend to be seasonal for several reasons. One is that people prefer indoor settings, which limits social distancing and significantly increases infection. Moreover, dryness and law humidity levels cause nasal and tracheal mucus to dry. As a result, the cilia lining the respiratory becomes less effective in preventing viruses and foreign bodies from entering the body.
Moreover, low temperatures in winters mean lower evaporation rates of virus-contaminated droplets, which are a main source of infection, and hence also mean higher infection rates. Meanwhile, there are other factors that decrease infection rates, such as high temperatures, high evaporation rates, longer sunshine duration, and the tendency of people to spend time in open spaces like beaches, which automatically achieves social distancing.
Humidity and Rain
When comparing some cities that were severely affected by the infection between January 2020 and March 2020, it was found that they are located at latitudes between 30 degrees and 50 degrees north, such as Wuhan in China, Tokyo in Japan, Paris in France, Milan in Italy, and Seattle in the USA, among others. The temperatures in those cities ranged between 5 C and 11 C, and absolute humidity (the total amount of water in the air) decreased to between 4 and 7 gram/cubic meter. This indicates that there is an inverse relationship between humidity and infection rates; with each increase in humidity of one gram/cubic meter, infection rates decrease by 67%, which is consistent with the typical behavior of respiratory viruses.
However, the study of equatorial rainy countries, characterized by high humidity levels, did not lead to the same results. These countries have witnessed a noticeable increase in the rates of influenza infections in humid, rainy climates. Brazilian scientists also confirmed that the coronavirus infections increased by 56 cases per day, coinciding with the increase in the rate of rain.
Temperature
Higher temperatures have been associated with lower rates of coronavirus infection in countries such as Brazil, Mexico, and Turkey; yet, the decrease appears to have limits. In other words, if the temperature continues to rise to very high levels, it would not lead to the elimination of the virus. This explains the infection rates discrepancy between high-temperature countries. Meanwhile, another group of scientists are not inclined to conclude that cold or hot weather is able to kill the virus. They say there is no relationship between the external temperature and the human body temperature, which remains constant between 36.5 C and 37 C, and hence is appropriate for the virus.
Also, no link was established between long sunshine durations and the decrease in COVID-19 infection rate; on the contrary, the infections increased, unlike other types of respiratory viruses, such as influenza. These findings can be an indication of the behavioral changes or variations the virus makes. As for ultraviolet radiation, it seems that it has absolutely nothing to do with the elimination of the coronavirus. Ultraviolet radiations need a wavelength of less than 280 nm, which does not actually reach the ground, but is absorbed into the ozone layer; otherwise, they would have caused severe skin and eye burns in humans within minutes.
Physicians and epidemiologists usually advise not to rely on findings that link between weather and climate, and infection rates for several reasons; one such reason is that the ability to conduct COVID-19 tests varies from one country to another. This implies that there are many unreported cases, and that establishing a link between the curve of infections and the weather is incorrect. Therefore, to make a long story short, the best protection measures—regardless of the changing seasons and temperature—are applying social distancing and constantly washing and sanitizing hands.
References
medicalnewstoday.com
sciencedirect.com
weforum.org
who.int
Cover Image: Sar photo created by freepik - www.freepik.com