A new scientific paper published on the preprint server medRxiv* shows that the spread of COVID-19, the respiratory illness that has spread across the world to kill hundreds of thousands in 2020, shows that weather conditions reduce the spread of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).
Novel Coronavirus SARS-CoV-2 Transmission electron micrograph of a SARS-CoV-2 virus particle, isolated from a patient. Image captured and color-enhanced at the NIAID Integrated Research Facility (IRF) in Fort Detrick, Maryland. Credit: NIAID
The spread of the novel coronavirus illness COVID-19 across countries and continents has been nothing short of terrifying, with the total toll having crossed 4.5 million in terms of infected cases, and over 300,000 deaths, in just over four months.
COVID-19 typically begins with fever, a dry cough, and shortness of breath develops later. The incubation period seems to be 5-6 days, on average, and not above 14 days. Most fatal cases terminate with acute respiratory distress syndrome and multi-organ failure.
The rapid spread of the virus prompted the World Health Organization (WHO) to call it a pandemic.
Climate and Viral Spread
Some climatic conditions can cause more significant interaction between the virus and humans, facilitating faster and greater contact and, therefore, more extensive host infection.
Other meteorological variables can lead to increased human-human interactions, and to the persistence of the virus on environmental surfaces, which can foster the spread of the infection from one human to another.
Earlier research on the correlation of weather conditions and the spread of the novel coronavirus have been conflicting. In Northern Europe, earlier studies have shown that influenza virus spread is more easily under cold conditions and an increased ultraviolet index.
A study from Jakarta, Indonesia, showed the only weather variable to show a significant correlation with the spread of the virus was the average temperature.
On the other hand, a recent Chinese study found that there was no link between heat or ultraviolet exposure and viral transmission.
Testing Weather-COVID-19 Associations In Japan
The current study was focused on determining whether this association was meaningful.
The study was carried out in Japan across all the prefectures. The total numbers of confirmed COVID-19 cases in each of them were collected in the period from January to April 2020. Similarly, the population density for each square kilometer of the inhabitable area was obtained for 2020. Finally, meteorological data was collected for each capital city of the prefectures over the same period.
The weather data included the monthly air temperature in degrees Celsius, the wind speed in m/s, the air pressure at sea level in hPa, the relative humidity in percentage, the percentage of possible sunshine, the monthly total for the duration of sunshine in hours, the amount of rain in mm, and the monthly average for maximum daily ultraviolet index.
To arrive at a more meaningful index of viral spread, the researchers calculated the total number of COVID-19 patients divided by the total population per 100 square kilometers of inhabitable area, which would compensate for gross differences in population density.
What Did the Findings Show?
The analysis of the data showed that the incidence of COVID-19 varied with the meteorological data. The number of new cases went down significantly with air temperature, air pressure, and ultraviolet radiation.
Caution: Human Behavior Ahead
Many other factors come into play, however, as explained by eminent epidemiologist Marc Lipsitch, of Harvard’s T. H. Chan School of Public Health. He lists at least four modifiers among environmental conditions that could influence viral spread:
- Dry cold conditions favor the spread of the flu virus because it is more stable and survives longer. This may not apply to SARS-CoV-2, which is able to make its way in widely different climate zones, from equatorial to Arctic zones.
- SARS-CoV-2 can survive for up to 72 hours on plastic and stainless steel surfaces between 21-23 oC) and with 40% relative humidity. At 4 oC they can survive for more than 28 days.
- People spend more time indoors during winter and are closer to each other, which favors the spread of respiratory pathogens. In the case of COVID-19, it is not clear whether children, for instance, get the infection as easily, or spread it less, or more, than adults do. This is an area where urgent research is needed.
- The host immunity may wane during winter, due to variations in the level of vitamin D, melatonin (a light-sensitive hormone which regulates the body’s circadian rhythms).
- The number of susceptible hosts in the population at any time may interact with the above factors to cause seasonal variation, as well as prompt seasonal epidemics. Since SARS-CoV-2 is a new virus, the low immunity level in the population is a crucial advantage that masks any potential seasonality.
The researchers conclude, “Higher air temperature, air pressure, and UV may be associated with less Covid-19 incidence, which should be confirmed by further epidemiological investigations taking other risk and protective factors of COVID-19 into account.”
However, scientists caution against pinning our hopes on weather changes rather than changes in human behavior in stopping viral transmission. Environmental researcher Miguel Araujo of Madrid’s National Museum of Natural Sciences warns, “This is not a one-variable equation. The virus spreads from human to human. The more humans at any given place and the more they get into contact with each other, the more infections there will be. Their behavior is key to understanding the propagation of the virus.”
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
- Tosepu, R., et al. (2020). Correlation Between Weather and Covid-19 Pandemic in Jakarta, Indonesia. Science of the Total Environment, Volume 725, 10 July 2020, 138436. https://doi.org/10.1016/j.scitotenv.2020.138436. https://www.sciencedirect.com/science/article/pii/S0048969720319495
- Lipsitch, M. (2020). Seasonality of SARS-CoV-2: Will COVID-19 go away on its own in warmer weather? Available at: https://ccdd.hsph.harvard.edu/will-covid-19-go-away-on-its-own-in-warmer-weather/. Accessed on May 15, 2020.
- Gray, R. (2020). Will warm weather really kill off Covid-19? Available at: https://www.bbc.com/future/article/20200323-coronavirus-will-hot-weather-kill-covid-19. Accessed on May 15, 2020.