COVID-19 Restrictions, Social Distancing, and Immune System Development

With the COVID-19 pandemic having placed everyone into a state of hygiene hypervigilance, social distancing, and mask wearing for over a year, many have worried whether our immune systems will be consequently weakened. For adults, this is unlikely to be a concern – most experts agree that by adulthood the immune system is fully developed, and giving it “rest” is not going to weaken it (Burling). For children who are still developing their immune system, however, public opinion is more skewed. The “hygiene hypothesis” – with its most well known claim being that an excess of hygiene may prevent microbial exposure and thus children’s immune systems from properly developing, leading to an increase in allergic and autoimmune diseases – has been repeatedly propping up in news articles on the topic.  While the original understanding of the hygiene hypothesis would understandably lead one to worry that COVID precautions will cause a generation of children with hyper-reactive immune systems, children growing up in the COVID-19 pandemic may still have access to microbial exposure to build their immune system up. 

Over the past year, news publications such as Business Insider, The Conversation, and The New York Times have published articles with headlines claiming that COVID lockdowns and quarantines will have an adverse effect on the development of children’s immune systems according to the hygiene hypothesis. These articles stress the importance of microbial exposure for children’s immune systems and suggest that the bulk of this interaction occurs through exposure to other adults and children. The Conversation and Business Insider’s articles are identical, both written by Byram W. Bridle, a professor of Viral Immunology at the University of Guelph, who warns against the COVID-19 restrictions effect on children’s immune systems. He writes that “most COVID-19 policies have maximized the potential for children to develop dysregulated immune systems” and predicts that there will “likely by a cluster of ‘pandemic youth’ that grow up to suffer higher-than-average rates of allergies, asthma, and autoimmune diseases” (Bridle). He goes as far as suggesting that COVID-19 is equivalent to the annual flu for children, condemning the restrictions that have been placed upon them, and closes his article with the words “let’s consider letting children be children again” (Bridle). 

The New York Times opinion piece, written by Columbia University’s professor of immunology Donna L. Farber and professor of pediatrics Thomas Connors, opens with the bold statement that “the world is unwittingly conducting what amounts to the largest immunological experiment in history on our own children” and claims that we may be “unintentionally inhibiting the proper development of children’s immune systems” (Farber). They claim that without the typical “everyday experiences of childhood – such as interactions with friends, teachers, trips to the playground, sports… we are altering the frequency, breadth and degree of exposures that are crucial for immune memory development” (Farber). They cite the studies on laboratory mice, where germ free mice have “reduced and altered immune responses to many types of pathogens” and “succumbed to pathogens that the pet mice were able to fight off,” as well as the clinical trials that found that early introduction of peanuts reduced the chances of a peanut allergy (Farber). Farber and Connors take a less aggressive stance than Bridle, however, advocating for children to “return to school and re-establish their normal routines” only once “teachers and caregivers can be vaccinated” (Farber). 

Bridle, Farber, and Connors’ claims are not entirely unsubstantiated. Sally F. Bloomfield’s study, which Bridle cited, surveys a wide range of research (using 135 different references) on immune system development and dysregulation, and found evidence that “interaction with microbes that inhabit the natural environment and human microbiome plays an essential role in immune regulation” (Bloomfield). She also agrees that “there is a window of time” when developing the microbiome is critical for the maturing of the immune system, and that “disruption or delay in acquisition of the microbiome in the first few years of life may predispose to later immune dysfunction”. Additionally, a study published by the National Institute of Health found that exposure to other children as a toddler, defined as the ages of 16 to 36 months, did have a protective effect against asthma risk, “independent of the number of respiratory tract illnesses a child experiences during this period” (Gurka 5). Yet, the validity of this study may be affected as it did not exclude those with a family history of asthma, and did not control for factors such as frequency of outdoor time, family size, or cleanliness of the house (Gurka). 

While there is some substance to the hygiene hypothesis and the proper development of children’s immune systems is righteously an area of concern, one’s level of hygiene and exposure to disease may not be the most important factor in a child’s immune system development. The original hygiene hypothesis in the late 20th century did speculate that children born in developed countries were more likely to develop allergic and autoimmune disease because they no longer “run the gauntlet of infectious diseases that they used to” (Yong 122). However, this hypothesis later shifted its emphasis “away from pathogens and more towards benevolent microbes” called “Old Friends” (OF), which can be found in the environment (Yong 122). In Bloomfield’s study, she similarly emphasizes OF exposure as the more crucial factor in immune system development, stating the while “the hygiene hypothesis implicated childhood virus infections as the vital exposures, from an evolutionary point of view this was never likely. Crowd infections were not part of the human evolutionary experience because they either kill or induce solid immunity” (Bloomfield). She furthermore notes that “microbial studies in westernised homes indicate that routine daily or weekly cleaning habits… have no sustained effect on levels of microbes in our homes” and that there is “no confirmed evidence of a link between personal or home cleanliness and increased risk of allergic diseases” (Bloomfield). 

There are multiple ways in which children can gain OF exposure that are not inhibited by COVID-19 protocols. The first Bloomfield touches upon is those that occur “during pregnancy, delivery, and the first few days or months of infancy”. She cites an external review of studies that show that “Caesarean section is linked to increased risk of allergy”, implying that natural births may be a crucial point of OF exposure. She also suggests that “breast versus bottle feeding has a large influence on gut microbiome” though she acknowledges that “further studies are needed to confirm any association with allergic disease” (Bloomfield). Studies also show that “children from large families are at lower risk of developing allergies” likely because the presence of other children contribute to the diversity of microbial exposure (Bloomfield). Later in life, “contact with microbial diversity from the natural environment is crucial” (Bloomfield). Though COVID-19 protocol may inhibit one’s ability to get outdoors, it is not altogether impossible and open air, green spaces are some of the few public spaces that remained open. Lastly, proper maintenance of the microbiome is an important consideration. Bloomfield claims that “the optimal composition of the microbiota is maintained by diet”, emphasizing a diverse and fiber rich diet. Asides from diet, antibiotics can “have lasting effects on the microbiota of young children and increase risks of asthma” (Bloomfield) as they “kill the bacteria we want as well as those we don’t” (Yong 125). 

While the hygiene hypothesis’s name suggests that personal and household hygiene is the main barrier to our microbial exposure, according to Bloomfield the more recent research demonstrates that there are a multitude of factors that are equally, if not more, important to our microbiome and immune system development. There has yet to be solid evidence that increased personal hygiene or decreased crowd infections have an adverse impact on our microbiome or immune systems. COVID-19 restrictions may provide a unique avenue to study immune system development, and specifically to research whether a lack of social contact and an increase in hygiene really does have an influence on immune system development.  Yet, current research indicates that natural birth, breastfeeding, family size, contact with the natural environment, a microbiome friendly diet, and antibiotic use appear to be the more crucial factors. COVID-19 restrictions are unlikely to affect these factors, aside from contact with the natural environment. For families who do not have access or the time to natural environments outside of schools and playgrounds, COVID-19 may have an impact on their children’s microbiome and immune system development. If a child from one of those settings is additionally an only child, who’s mother underwent a Cesarean Section and chose to bottle feed, and has a constricted, fiber-deficient diet coupled with the taking of antibiotics, then that child may have reason for concern. However, by taking each of these factors into consideration, it seems unlikely that there will be a full generation of “pandemic youth” with dysregulated immune systems.

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