In March 2020, the World Health Organization (WHO) declared Covid-19 to be a pandemic due to the worldwide outbreak of the novel coronavirus (SARS-CoV-2). Scientists are not only working on the development of a vaccine for Covid-19 but are also working tirelessly to understand the correlation between various external factors (e.g. air pollution, temperature, humidity, etc.) and virus transmission.
Research conducted by van Doremalen and group has shown that SARS-CoV-2 remains alive and infectious in PM2.5 particles (particles with an aerodynamic diameter less than 2.5-micron present in the air) for many hours suggesting an airborne route of Covid-19 transmission.
In another study, scientists recorded the data from two heavily polluted Italian metropolitan areas (Milan, Lombardy (the epicenter of a virus outbreak in Italy) and Florence, Tuscany) and the independent province of Trento. The data was recorded for a period of 103 days from 09 March 2020 to 19 June 2020. It included variables like the daily Intensive Care Unit (ICU) admissions, virus transmission rate, air pollution levels, and other meteorological variables.
Following the data collection, the scientists fitted a Gaussian Mixture Model (GMM) to the number of patients admitted to the ICU and obtained the residuals. The residual is a different variable from the others because the number of daily new positive infections is independent of the number of tests conducted.
The conclusion drawn from this study stated that physical variables such as temperature, humidity, and water vapor are negatively correlated with the virus infection. However, PM2.5 concentration is positively correlated (at a lesser degree) with SARS CoV-2 transmission. This result also signifies the possibility that air-conditioned settings without sub-micron filters for organic particulate may aid in virus transmission.
Researchers in the US have also reported a similar result. Their research suggested that air pollution has significantly escalated Covid-19 transmission. Thereby, in other words, air pollution has played an important role in the rapid transmission of the virus which has subsequently led to an increased number of deaths. The research team led by Rachel Nethery and Xiao Wu at Harvard University’s T.H. Chan School of Public Health, states that an increase of 1 microgram per cubic meter in long-term PM2.5 exposure may bring about an increase of 8% Covid-19 deaths.
So, what is the internationally agreed safe threshold for air pollution levels? The US Environmental Protection Agency sets the safe air quality standard at 12 μg/m3 annually for PM2.5. However, the WHO recently revised this number and reset it at 10 μg/m3, as an annual mean. In New York City, the level of the atmospheric particulate matter remains consistently above these safety limits. This could be one of the main reasons for the severe outbreak of coronavirus infections in New York State. The number of deaths in New York as of November 20, 2020, is reported as 34,215 which is by far the highest among all other US states.
Based on these studies, an association between PM2.5 and SARS-CoV-2 appears to exist. This association is positively influencing the incidence and transmission of Covid-19.
