The COVID-19 pandemic has highlighted fundamental truths about infectious disease in humans. First, the makeup of our societies helps determine who is vulnerable to disease by shaping the risks and protections that dictate pathogen exposure. Second, infectious disease is a social phenomenon, whether it’s pathogens moving between people, the collective efforts necessary to minimize transmission, the role of caregivers, or the effect of sickness — and, unfortunately, mortality — on families. Furthermore, a growing body of literature suggests that the social conditions in which we live can even influence our immune systems.
The power of our social lives over our health and wellbeing is not trivial, nor is it new. We humans are not particularly well equipped for survival, relative to other animals. We’re not very fast or strong. We’re devoid of fang and claw and our senses are mediocre. But we’ve managed to survive as a species for roughly 300,000 years and spread from Africa to every habitable area of the planet — and even some marginally habitable ones. We have accomplished this, in part, by being very good at being social.
In fact, it’s reasonable to hypothesize that because our sociability has contributed so much to our survival over our evolutionary history, any threats to our “social safety” are felt more strongly by our mind and body and therefore cause a greater biological reaction than other stressors.
This reaction includes inflammatory and immune responses, likely to protect against injury and subsequent infection, harkening back to our evolutionary history. Over the last 300,000 years, of course, our social systems have become increasingly complex. Each of us is bound up in multiple interconnected levels of social interaction, from our individual networks to our place in wider society.
We are further embedded in our culture(s), that “internalized and shared framework” through which we experience the world.
Understanding precisely how these different social forces intersect to shape our immune responses is the goal of what, in my review article for BBI Health, I have called “social immunology.”
There is evidence that social connections affect our immune systems. For example, social integration is linked with lower circulating levels of multiple inflammatory markers, like C-reactive protein (CRP) and pro-inflammatory cytokines. While inflammation is an important component of immune responses, chronic inflammation is associated with several negative health outcomes, like cardiovascular disease and cancer. An unrestrained inflammatory response is also a component of the so-called “cytokine storm,” which contributes to COVID-19 mortality. People with a more diverse social network were also less likely to develop a symptomatic cold after experimental exposure to the virus.
However, social relationships can also impose health costs. More interpersonal contacts mean more opportunities to come into contact with pathogens, and some research suggests that frequent pathogen exposure can contribute to accelerated immune system ageing and a decline in efficacy.
Additionally, perceived social role conflict — that is, the degree to which our various social responsibilities conflict with each other — has been linked with greater inflammatory responses.
As noted above, chronic exposure to inflammatory factors can be unhealthy. While elevated inflammation might help fight off infections faster in the short term, chronic social role conflict could lead to a greater inflammatory burden and downstream health consequences. So, while social integration and healthy relationships are generally a net positive, our social lives are highly complex.
It takes time, effort, and attention to maintain our multiple personal and professional social relationships and roles, and this can come at a cost. What’s more, our networks and social roles are shaped by wider societal institutions.
These institutions — things like families, governments, and economic systems — constrain our behaviours through ideologies, rules and norms, and other forms of explicit or implicit guidance. A considerable amount of research shows that factors like work/unemployment status, social support, adequate nutrition, and other social determinants of health (SDoH) affect multiple health domains.
The COVID-19 pandemic has highlighted how unequal burdens of chronic health conditions and health behaviours can affect morbidity and mortality. For instance, asthma — an important underlying COVID-19 vulnerability, is frequently associated with low socioeconomic status, smoke exposure, and racial/ethnic minority status. Indeed, systemic discrimination and racism can lead to chronic inflammation and accelerated biological ageing, again contributing to diminished immunity.
Adequate nutrition is another SDoH that can affect immunity. Malnutrition affects the ability of immune cells to differentiate and replicate, so it is linked with increased infectious disease susceptibility.
Obesity — a state of malnutrition due to increased consumption of energy-rich foods — is also implicated in reduced immune function, including decreased influenza vaccine efficacy.
Much as economic systems and governments set behavioural parameters, so do cultures. Cultural norms like stoicism or gender roles can influence symptom appraisal and health-seeking behaviour. But there is also intriguing research suggesting that differences in norms surrounding negative emotions between the US and Japan can shape biological responses to these emotions, with generally lower inflammation among the latter.
Importantly, we shouldn’t think of cultures as monolithic (that is, one “American culture” for instance). Instead, we often navigate and engage with cultures differently and embody multiple culturally constructed identities. Like social role conflict, conflicting cultural frameworks can be a significant stressor. In one study in Western Samoa, more exposure to non-traditional cultural influences and subsequent stress of navigating between traditional and non-traditional cultural norms was linked with immunosuppression.
Given these different lines of evidence, it becomes clear that immunity is affected by social factors across multiple levels. Crucially, none of these levels are independent of the others. Despite the evidence outlined above, further research is required to better understand the impact of social factors on immune function. While we can observe white blood cell counts or inflammatory markers rise or fall in association with social stress, nutrition, or cultural incompatibility, direct evidence of either improved or impaired ability to fight infections is necessary.
The COVID-19 pandemic has driven home the impact that pathogens can have on individuals and societies, but infectious diseases are a significant public health risk even outside of pandemics. For instance, there were an estimated 54.5 million cases of lower respiratory tract infections attributable to influenza in 2017. Around 8 million of these were severe, with about 145,000 deaths. Like COVID, influenza can lead to health complications, such as cardiovascular events. Understanding who is at higher risk for contracting flu, COVID, tuberculosis, HIV, or other diseases is critical to public health.
Social immunology can help identify the most vulnerable, such as immigrants facing conflicting cultural norms combined with potentially low social support and systemic barriers to accessing healthcare.
Social immunology calls attention to the complex interactions between biology, social institutions, interpersonal relationships, and cultural milieus and reminds us that we are, at the core, social animals. Our social environments, then, should be treated with as much care and consideration as our physical environments.