Thousands of COVID-19 cases and deaths in California, Oregon, and Washington between March and December 2020 may be attributable to wildfire smoke, according to a new study released Aug. 13 by researchers at the Harvard T.H. Chan School of Public Health.
The study, published in the journal Science Advances, looked at the connection between county-and daily-level data on fine particulate matter — PM 2.5 — and the number of COVID-19 cases and deaths in 92 counties across California, Oregon, and Washington. The researchers accounted for factors such as weather, population size, and societal patterns of social distancing and mass gatherings.
University of California San Francisco pulmonologist John Balmes explains the correlation between exposure to wildfire smoke and greater vulnerability to COVID-19. Balmes — who has studied California’s air pollution for more than three decades, and who served on the California Air Resources Board — says people of color are at greater risk because many live in regions that consistently suffer from poor air quality.
The increased risk related to wildfire smoke further supports the importance of COVID-19 vaccinations, according to Balmes. “Vaccines are doing their job,” he says. Public health experts are hopeful that the recent FDA approval of the Pfizer vaccine will offer an additional nudge to those who have been hesitant to get vaccinated.
The UCSF Professor of Medicine is the Chief of the Division of Occupational and Environmental Medicine at San Francisco General Hospital, and Director of the Human Exposure Laboratory of the Lung Biology Center. Balmes is also Professor of Environmental Health Sciences at the University of California, Berkeley, where he is the director of the Northern California Center for Occupational and Environmental Health and the Center for Environmental Public Health Tracking.
In this FAQ, Balmes explains how individuals can mitigate their exposure to polluted air.
EMS: Is there a clear correlation between exposure to wildfire smoke and a greater vulnerability to COVID-19? Please explain how this happens.
Dr. Balmes: The research on wildfire smoke and COVID-19 is limited, but the results of at least two recently published studies show an association between exposure to the fine particulate matter (PM2.5) in wildfire smoke and increased risk of COVID-19. The Harvard study also shows an association between wildfire smoke PM2.5 and risk of infection with the novel coronavirus.
There are more published studies of the association between non-wildfire PM2.5 and COVID-19 outcomes. It is felt that PM2.5 from any combustion source, whether from cigarette smoke, diesel trucks, or wildfires, inhibits the immune response to the virus.
One mechanism by which this happens is overloading of the cells in our deep lungs that are the first line of defense against lower respiratory tract infection, alveolar macrophages (AMs), with particles which are toxic to their function. In other words, the AMs are full of smoke particles that inhibit their ability to properly respond to the coronavirus.
EMS: Many people of color live in regions which routinely have poor air quality, irrespective of wildfires. Have we been at greater risk throughout the pandemic?
Dr. Balmes: Yes, low-income people of color have a disproportionate burden of exposure to air pollution, primarily due to diesel emissions from trucks, railyards and ports in California, as well as from power plants and industrial sources.
People of color are also at greater risk of COVID-19 for reasons other than greater exposure to air pollution.
EMS: Should fully vaccinated people also be concerned, given the increasing numbers of breakthrough infections?
Dr. Balmes: While breakthrough infections are occurring — at a relatively low rate — the vaccines are doing the job of protecting people who are vaccinated from getting very sick, including hospitalization and death..
EMS: How can people mitigate the risk to themselves and their families? What types of masks are particularly effective in filtering out particulate matter? How effective are home air purifiers?
Dr. Balmes: During episodes of poor air quality due to wildfire smoke, people should reduce their exposure by staying inside with the windows closed and trying to clean the air in their homes.
Clean air can be achieved by putting a MERV 13 filter in a home with central ventilation and turning the ventilation system to recirculate. In a home without central ventilation, you can clean a room with a portable HEPA air cleaner – the cheapest ones that are good cost $160-$200. If this is too expensive, you can DIY by placing a MERV 13 filter that can be purchased at any hardware store over a box fan. There are YouTube videos that show how to do this.
If you have to go outside during poor air quality from wildfire smoke then N95 respirators are the best mask to use. Cloth masks don’t provide any protection against wildfire smoke PM2.5; surgical masks provide less than 20% reduction exposure; N95s reduce exposure by 80% or more.
EMS: You have stated in previous interviews that this is an environmental justice issue. How can local municipalities mitigate risk for their residents?
Dr. Balmes: Local governments could provide portable HEPA air cleaners and N95s to low-income communities of color. They could also help weatherize homes so there is less penetration of wildfire smoke PM2.5.
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