Viruses or bugs that cause respiratory diseases have been known to increase during cold seasons or when temperatures are low.
For instance, influenza viruses are often responsible for seasonal flu outbreaks in cold weather periods.
In the case of the Covid-19 pandemic, areas worst hit by the disease have been in regions with cooler temperatures, such as the US and Europe that were in the spring season.
The virus that causes the disease, which is known as SARS-CoV-2, comes from the family of bugs known as coronaviruses that have been linked to ailments such as the common cold and pneumonia.
A past study conducted by the Centre for Infectious Diseases at the University of Edinburgh, UK, found that three coronaviruses – all obtained from patients with respiratory tract infections showed “marked winter seasonality”. This is because the viruses seemed to cause infection during the cold seasons and wane as hot weather ensued.
Consequently, as Covid-19 has spread across the globe, questions have been raised about whether warming temperatures, humidity and ultraviolet (UV) index might slow, or even halt, the spread of SARS-CoV-2. Humidity refers to the amount of water vapour in the atmosphere. Hot places tend to be more humid than cool areas since heat causes water to evaporate faster.
The ultraviolet (UV) index on the other hand, refers to the strength of UV radiation that is released by the sun at any particular time. Generally hot areas are associated with high UV radiation.
According to health experts, knowledge on the impact of temperatures on Covid-19 transmission is of interest as warmer months ease in and affected countries in Europe or states in the US consider and implement reopening plans.
In sub-Saharan African countries like Kenya, the knowledge can also offer insights on how the disease is likely to behave in a continent that largely enjoys warm weather for most part of the year.
To answer these questions, researchers at Mount Auburn Hospital looked at the impact of temperature, precipitation, and UV index on Covid-19 case rates in the United States during the spring months of 2020 (January to April).
The findings of the study, which were published in the Clinical Infectious Diseases Journal, revealed that the rate of Covid-19 incidence does decrease with warmer temperatures up until 52 degrees Fahrenheit (10 degrees Celsius).
But any further increase in temperature beyond that was found to have no significant effect on the spread of the disease.
The study revealed that a higher UV index also assists in slowing the growth rate of new cases. However, the overall impact remains modest.
Precipitation patterns on the other hand, did not appear to have any effect on virus transmission.
During the study, the research team analysed daily reported cases of Covid-19 infection across the United States from January through April, as tracked by the John Hopkins University's COVID-19 Dashboard.
They relied on temperature, precipitation and UV Index measurements from the US National Centres for Environmental Information.
"While the rate of virus transmission may slow down as the maximum daily temperature rises to around 50 degrees Fahrenheit (10 degrees Celsius) the effects of temperature rise beyond that don't seem to be significant,” said Dr Shiv Sehra, the first author of the study and director of the Internal Medicine Residency Programme at Mount Auburn Hospital.
"Based on our analysis, the modest association suggests that it is unlikely that disease transmission will slow dramatically in the summer months from the increase in temperature alone," noted Dr Sehra, who is also an assistant Professor of Medicine at Harvard University Medical School.
Due to its proximity to the equator, Kenya generally enjoys warmer temperatures - averaging between 20 and 28 degrees Celsius - all year round.
Judging from the findings of the study, these favourable weather conditions are likely to have minimal impact on the spread of the disease in the country.
These insights are in line with calls from health experts who have warned Kenyans against throwing caution to the winds, and ignoring recommended Covid-19 prevention strategies, with the false assumption that high temperatures will protect them from the coronavirus disease.
As Covid-19 is a new condition that scientists are still trying to understand, the World Health Organisation notes that there is insufficient evidence to determine - with certainty - the impact of temperature variations on the transmission of the disease.
Whereas the pandemic began in China during the winter season and proceeded to hit Europe and US at a time when these regions were experiencing cold weather, scientists observe that the disease also spread very fast in nations such as Australia and Iran that were experiencing warm and humid weather.
In addition, strains of viruses may also change in certain environments, thereby enabling the bugs to survive and thrive in various geographical regions.
As such, health experts note that it is important for people not to take chances. They should continue to protect themselves and those around them by practising social distancing, wearing masks in public and washing hands frequently with soap and water.