“Mask up!” – a familiar phrase that most of the world has grown accustomed to as the COVID-19 pandemic unfolded in the past 3 years. In Singapore, mask-wearing regulations were recently loosened, leaving healthcare institutes as the only places with necessitated mask-wearing. After reading this blog entry, however, you might very well choose to continue wearing your mask even if it is no longer required to do so in your country.
According to Weaver et al. (2022), air pollution exposure undermines one’s immunity system and increases the likelihood of respiratory viral infections (such as COVID-19) in 2 ways: heightened risk of comorbidities and weakened immune functions that raises susceptibility. More specifically, inhaled particulate matter stimulates the upregulation of proteins that allow the SARS-CoV-2 virus to enter host cells, translating to higher viral loads and stronger symptoms of COVID-19. Particulate matter, NO2, and ozone undermine the body’s “first line of defence against invading pathogens”, causing inflammation. Hence, individuals with a history of long-term exposure to such air pollutants are more prone to more severe COVID-19 infections
Figure 1. Mechanisms through which various environmental conditions (including air pollution) influences susceptibility to and severity of COVID-19 infections (Weaver et al., 2022)
These findings are supported by Li et al. (2020)’s study which noted that the airborne transmission of respiratory diseases is aggravated by the longer residence time of viruses that attach to particulate matter. The authors discovered a positive relationship between the number of COVID-19 cases and the daily concentrations of various air pollutants in Wuhan, the Ground Zero of COVID-19.
Figure 2. Correlation between daily COVID-19 incidence and ambient air pollution in Wuhan (Li et al., 2020)
Academics continue to hold contrasting opinions with regards to the true relationship between air pollution and spread of infectious diseases like COVID-19. For instance, Kogevinas et al. (2021) suggest that the consequences of exposure to air pollution are limited to that of post-infection severity, and Yu et al. (2022) propose that COVID-19 transmissions are “more likely” due to indoor settings rather than outdoor air pollution. Meanwhile, Zhu et al. (2020) cited a 7.79% decrease in COVID-19 cases following a 10 μg/m3 increase in SO2 exposure, thereby nuancing the matter at hand further.
The diverse pool of perspectives and findings warrant further research into this relatively new field of air pollution for a clearer understanding of its relationship with the spread of COVID-19. Nonetheless, given that air pollutants are proven to hamper our bodies’ respiratory functions and immunity, it seems wiser to err on the side of caution. So… will you continue to mask up outside?
Until the next entry, breathe safe and be safe!
References
Kogevinas, M., Castaño-Vinyals, G., Karachaliou, M., Espinosa, A., de Cid, R., Garcia-Aymerich, J., Carreras, A., Cortés, B., Pleguezuelos, V., Jiménez, A., Vidal, M., O’Callaghan-Gordo, C., Cirach, M., Santano, R., Barrios, D., Puyol, L., Rubio, R., Izquierdo, L., Nieuwenhuijsen, M., … Tonne, C. (2021). Ambient air pollution in relation to SARS-COV-2 infection, antibody response, and covid-19 disease: A cohort study in Catalonia, Spain (COVICAT study). Environmental Health Perspectives, 129(11). https://doi.org/10.1289/ehp9726
Li, H., Xu, X.-L., Dai, D.-W., Huang, Z.-Y., Ma, Z., & Guan, Y.-J. (2020). Air pollution and temperature are associated with increased COVID-19 incidence: A time series study. International Journal of Infectious Diseases, 97, 278–282. https://doi.org/10.1016/j.ijid.2020.05.076
Weaver, A. K., Head, J. R., Gould, C. F., Carlton, E. J., & Remais, J. V. (2022). Environmental factors influencing COVID-19 incidence and severity. Annual Review of Public Health, 43(1), 271–291. https://doi.org/10.1146/annurev-publhealth-052120-101420
Yu, Z., Bellander, T., Bergström, A., Dillner, J., Eneroth, K., Engardt, M., Georgelis, A., Kull, I., Ljungman, P., Pershagen, G., Stafoggia, M., Melén, E., Gruzieva, O., Almqvist, C., Andersson, N., Ballardini, N., Bergström, A., Björkander, S., Brodin, P., … Schwenk, J. (2022). Association of short-term air pollution exposure with SARS-COV-2 infection among young adults in Sweden. JAMA Network Open, 5(4), 1–12. https://doi.org/10.1001/jamanetworkopen.2022.8109
Zhu, Y., Xie, J., Huang, F., & Cao, L. (2020). Association between short-term exposure to air pollution and COVID-19 infection: Evidence from China. Science of The Total Environment, 727, 138704. https://doi.org/10.1016/j.scitotenv.2020.138704