Among the many questions surrounding the Covid-19 pandemic, this one might be the most crucial: Why are some individuals who have been infected harder hit than others? We know underlying conditions account for some disparities, but there’s variation in impact even among those with such conditions.
In the field of chemical risk assessment and toxicology, we have been asking ourselves if some of this differential response could be explained by an individual’s previous chemical exposure. The U.S. population is at risk for exposure to multiple, ubiquitous chemicals that are known to adversely impact the immune system, making it more difficult to fight off infections such as Covid. Among this class of chemicals are per- and polyfluoroalkyl substances (PFAS).
PFAS is a group of chemicals that have been referred to as “forever chemicals” given that, once in the environment, they are present more or less in perpetuity. These man-made substances have a variety of uses in commercial products, firefighting foams, food packaging, and water and stain repellents.
Certain chemicals in this class have been evaluated by the country’s top toxicological research agency, the National Toxicology Program, and have been found to be directly associated with adverse effects on the immune system. Other researchers have found associations between PFAS and a wide range of serious health impacts, including reproductive, developmental, endocrine effects, and increased risk of some cancers.
While many questions still remain about the potential impact PFAS exposure can have on the immune system, a review of the existing literature offers some insight into how these chemicals may be exacerbating the effects of Covid, and suggests some additional areas of inquiry.
PFAS Impacts the Immune System’s Memory
The human immune system is comprised of two response mechanisms that defend the body against harmful invaders: innate immunity and acquired immunity. Innate immunity is your first line of defense against an infectious agent and confers broad, non-specific protection from various pathogens. Sneezing, coughing, and fever are part of your innate immune system.
The acquired immune system is made of a highly complex set of cells, receptors, and communication mechanisms that remember what pathogens your body has been exposed to in the past and how you fought them off. This allows for specific responses to be initiated in the body to respond quickly and efficiently when you’re re-exposed to these pathogens.
Studies have found PFAS have a particular impact on your acquired immune system. A disruption of the normal levels of these cells in either direction can be detrimental to health.
With too little of these cells your body may not efficiently fight off a pathogen. With too much activity from these cells your body may experience chronic inflammation, which is associated with a range of health effects such as diabetes, arthritis and cancer. In some studies, the cells of the acquired immune systems are observed to be suppressed by chemical exposure while, in others, PFAS exposure appears to result in over activity of the cells.
In addition, studies have also observed decreased rubella and influenza vaccine effectiveness in children, as measured by antibody levels, when comparing individuals with higher PFAS exposure to lower levels of exposure. Further, other research has also demonstrated a positive association with PFAS exposure and the risk for hospitalization due to infectious disease in female children. These are fairly notable findings in the context of the Covid pandemic.
There Is Much More to Understand
There are numerous data gaps that substantially hinder our ability to truly understand the effects of PFAS exposure on the immune system. Only 2% of toxicity studies on PFAS chemicals evaluated the effect of long-term exposure to PFAS and subsequent health effects.
There is a lack of understanding of the impact a pregnant mother’s exposure to PFAS can have on her children, and there is little to no data on the effect of PFAS on already immunocompromised individuals. Studies that follow individuals who have been exposed to PFAS for many years may help fill some of these data gaps. In addition, using readily available data such as the Centers for Disease Control and Prevention’s NHANES data sets might give us a better understanding of these chemicals’ effects, which could motivate action to remove them from our drinking water, and reduce their production and use.
Further, geo-spatial mapping combined with rigorous statistical analysis of the relationship between Covid infections and potential exposure to immunosuppressive chemicals such as PFAS in drinking water will allow us to further understand the relationship between exposure to these chemicals and one’s outcomes when infected with Covid.
One thing we do know: we need to mitigate exposure to these chemicals to give people the greatest chance to fight off both novel, and well-established, pathogenic threats.
This column does not necessarily reflect the opinion of The Bureau of National Affairs, Inc. or its owners.
Lauren Brown is a board-certified toxicologist with more than a decade of chemical risk assessment experience. She is a senior scientist for Abt Associates, supporting a multitude of federal agencies by applying rigorous scientific methods to inform policy decisions.