Mahi Wants You Healthy and Happy – A column using science to focus on physical health and myths associated with disease.
On March 11, 2020, the World Health Organization (WHO) categorized COVID-19 as a pandemic: the first pandemic caused by a coronavirus. At this time, there were more than 118,000 cases in 114 countries and 4,291 people had lost their lives. Since then, the virus has propagated tremendously with over 7.1 million confirmed cases worldwide, and over 1.6 million deaths. The rapid rise of COVID-19 can be attributed to many factors, among those include the lack of preparedness, shortage of PPE, the dearth of a coordinated national plan, and the loose implementation of safety regulations. Currently, due to the surge of coronavirus cases and hospitals in some areas stretching to capacity, states all across the U.S. have lockdown and stay-at-home orders. As COVID-19 continues to spread globally and with the looming reality of a second wave, it is important to understand the factors that affect the transmission of COVID-19. This article explores the effect of temperature and humidity on the transmission of COVID-19.
Cold Weather and Transmission of COVID-19
One study, which looked at epidemiological data of COVID-19 reported by WHO, provided preliminary evidence that the COVID-19 pandemic may be partially suppressed with increases in temperature and humidity. The study used a generalized additive model (GAM) to obtain its results and had a 95% confidence interval. GAM is an additive modeling technique where the impact of the predictive variables (in this case temperature and humidity) is captured through smooth functions; smooth functions are functions whose derivative is continuous in the domain that is captured in the GAM. It is important to note that a 95% confidence interval is considered relatively good statistically especially with the large population sample that the data provided. However, this study is limited by its use of available data which is often dependent on other variables.
Various studies have been done on viruses that are genomically similar to the coronavirus. Studies on these viruses have also suggested a positive correlation between heat and humidity and virus transmission. For example, a published laboratory study on SARS-CoV, responsible for the outbreak of SARS in mid-November 2002, showed that increased heat and humidity leads to lower infection viability of the virus.
It is important to note that other studies have shown contradictory results, particularly regarding humidity. One study researched the effects of relative humidity, temperature, and wind speed on the transport and viability of COVID-19 in saliva droplets. It found that high humidity facilitated sufficient droplet travel and COVID-19 viability. The scientific explanation for this phenomenon is explained by the theory of heat and mass transfer. The computerized theoretical transient (meaning impermanent) correlations describe the heat and mass transfer at the microscopic scale of contaminated droplets. Then they used it in tangential with a program that mimicked saliva sprays from a 1.7 m tall human to get their results.
The association with low temperature and infectibility is corroborated by another contagious respiratory illness, the seasonal influenza viruses. They are most common during the fall and the winter and while infection by these viruses can occur year-round, it is important to note their peak during the colder months.
Despite the continuous investigation of the effects of temperature and humidity on transmission, there is still too much inconsistency and uncertainty to come to a conclusion. Discrepancies in results can result from non-environmental factors, which include changes in social behavior. It is still important to actively protect yourself and others from infection by wearing a mask in public, washing your hands frequently, and practicing respiratory etiquette. While the COVID-19 vaccine is rolling out and the arrival of the Omicron variant, let us continue to limit the spread of this virus to keep everyone safe.
Mahi Ravi is a senior at Saratoga High School who is dedicated to getting more vaccinators in line for the COVID shot. In her free time, Mahi leads a website The Corona Page that offers simplified research on COVID.
Sharon Tu is currently a Biological Science major with a minor in Health Care Studies and Chemistry at USC. At school, she is a peer health educator and an undergraduate research assistant at USC HEAL and Feakins Leaf Wax lab.