Does climate play a large role in SARS-CoV-2 transmission?

By Dr. Priyom Bose, Ph.D.Feb 19 2021

The emergence of the novel coronavirus disease (COVID-19) was first reported in Wuhan, China, in December 2019 and its rapid spread across the world has caused the World Health Organization (WHO) to announced a Public Health Emergency of International Concern (PHEIC). COVID-19's causative pathogen – severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) – is highly contagious and spreads rapidly through the respiratory droplets from infected individuals. Most people infected with COVID-19 develop mild symptoms or are asymptomatic. For the others, it may cause acute respiratory problems, severe health issues and in some cases, it may also prove to be fatal.

Scientists across the globe have been fighting to curb the spread of the disease by devising various approaches such as the development of vaccines, nasal sprays, sophisticated masks, oral medicines, and many more. They are also working to establish valid links between environmental conditions and the coronavirus infection rate to develop a better understanding of the nature of the virus and how it spreads.

In a new paper released on the medRxiv* preprint server, a team of researchers from the Universidade Federal de Itajuba in Brazil has reported that weather plays a vital role in determining the transmission rate of SARS-CoV-2 infection. They have further stated that after controlling for parameters such as age, population, and urbanization, the meteorological variables are highly significant for predicting mortality rates of a region. During the early days of the global outbreak of COVID-19 in early 2020, it was wrongly assumed that the virus thrives only in cold conditions. However, the subsequent intense spread of the coronavirus in many tropical countries such as Brazil and India have challenged this misconception.

Study: Are there significant correlations between climate factors and the spread of COVID-19 for less densely populated and less polluted regions? Image Credit: Andrii Vodolazhskyi / Shutterstock

*Important notice: medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Recently, the correlation between the spread of SARS-CoV-2, and meteorological variables such as temperature, wind speed, relative humidity, and precipitation of urban-rural sparsely populated cities located in southeastern Brazil was analyzed. For this study, researchers collected meteorological data for the six study locations from the Federal University of Itajubá (UNIFEI, 2020) and the National Institute of Meteorology (INMET, 2020) for the period of April to December, 2020. The daily data of COVID-19 cases were procured from the database of the Secretary of Health of the Government of Minas Gerais state (SHGMG, 2020). The correlation study was conducted using Spearman's correlation coefficient.

In the first year of the pandemic, the study revealed a lower incidence of COVID-19 in less densely populated areas (i.e., the study area for the experiment). This is in contrast to the high infection rates in other more populated regions of Brazil. Scientists initially hypothesized that the lower number of cases was perhaps due to the better air quality in smaller cities.

Many prior studies have suggested that relative humidity plays a significant role in the persistence and transmission of the virus in a closed environment or indoors. An increase in virus transmission takes place when relative humidity is low. Similar studies conducted in various regions of the world such as New York City, Chinese provinces, and South American regions indicated a significant correlation between the daily incidence of COVID-19 cases and absolute humidity. The current study under consideration further confirmed that irrespective of the level of pollution, the rate of transmission of the virus is high at lower levels of relative humidity.

Many scientists have also reported that maximum and minimum temperatures are positively correlated to virus transmission. The current research corroborates these findings and indicates that an increase in temperature and a decrease in relative humidity aid in the transmission of the SARS-CoV-2 virus.

In many cities, wind speed showed a positive correlation with the incidence of COVID-19. However, researchers claim that this result might not be conclusive because of various reasons. For example, wind speed disperses pollutants present in the atmosphere. In the regions where the wind speed is high, a lesser amount of contaminant prevails. Further, wind speed varies from one region to another; for instance, coastal regions will have greater wind speed than inland. Therefore, more research is required to determine a correlation between the COVID-19 incidence and wind speed.

Researchers have further reported that daily accumulated rainfall and COVID-19 infection are not correlated. However, in another study conducted in Oslo, Norway, scientists found a significant correlation between lack of precipitation and increased COVID-19 cases.

The current study helps the scientific community to understand the relationship between climatic conditions and the spread of SARS-CoV-2 in the less densely populated regions. Such evaluations assist the scientists in designing preventive measures to stop the spread of the disease and thereby contain the pandemic. The outcome of this research is also expected to assist in the framing of appropriate and more efficient mitigation policies, against the spread of SARS-CoV-2, on the basis of local climatic profiles.

*Important notice: medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.