What we can learn from evolutionary science

The mark of evolutionary success is survival and reproduction. Natural selection describes the process by which those organisms that are most suited to their environment have the best chance to survive and reproduce and their genes are therefore propagated. Evolution has no foresight and only has the past to go on and thus does not prepare us for just one optimal future condition. On the contrary, there are often a wide range of possible environments and there are also many different strategies that can be successful. For example, in a benign environment, it makes sense to delay reproduction, have fewer children and invest more in each. This is typical of a ‘slow life history’. On the other hand, if the environment is harsh and survival is not certain, those people who follow a ‘fast life history’ and reproduce early and have more children have a greater chance of leaving living descendants.^{Reference Arnot, Brandl, Campbell, Chen, Du and Dyble10}

People who have been oppressed and whose fertility has been curtailed will be much more sensitive to threats to their future reproduction. This is the case for ethnic minorities and for people who live under conditions of high deprivation. Nesse described how the functioning of the anxiety system is akin to a smoke detector.¹¹ It is evolutionarily sensible to overreact to avoid a potentially catastrophic danger (a false positive), rather than be complacent and die (a false negative) or be unable to leave descendants. Therefore, the widespread fear that the vaccine may reduce fertility^{Reference Diaz, Reddy, Ramasahayam, Kuchakulla and Ramasamy12} is highly salient, despite the lack of scientific evidence to support this fear. It may, therefore, not be a coincidence that the vaccination rate in older people is close to 100%, whereas almost 1 in 10 of 22- to 25-year-olds are not vaccinated.³ Of course, a further explanation is that COVID-19 has a disproportionate impact on the elderly compared with the young.

Detecting and avoiding threats is a crucial skill shaped by natural selection. When this ability is triggered unnecessarily (false positive), it may be expressed as conspiratorial thinking and even paranoia. However, where there has been a proven threat in the past, humans have generally adapted to be more careful in future. Post-traumatic stress disorder (PTSD), with the symptoms of hypervigilance, avoidance of similar situations and re-experiencing of trauma, is, in moderate levels, evolutionarily adaptive in that it keeps us on our toes, keeps us safe and does not let us forget. This can help us avoid a future catastrophic danger and therefore allows us to survive and reproduce. However, PTSD can be excessive, as seen in clinical cases, being seen as an extreme of such an adaptation and a mismatch with modern environments.^{Reference Zefferman and Mathew13}

The role of widespread misinformation should also be considered. Ironically, even before the pandemic, social psychology researchers proposed that an ‘inoculation’ of facts in the era of fake news may be needed.^{Reference Schmid and Betsch14} Such an approach would build on trust and counteract unhelpful impulsive decisions in the context of emotionally salient information. Given the fast pace of changing information during the pandemic, people who have persistent trust issues may be drawn into more extreme views. A line of evidence showed that a shift to extreme views is associated with impulsive decisions based on imperfectly processed evidence.^{Reference Zmigrod, Eisenberg, Bissett, Robbins and Poldrack15} One might argue that vaccine misinformation hijacked the trust systems that pushed the limits of an adaptive system interfering with decision-making even in the face of compelling evidence of vaccine effectiveness. Widely available access to social media platforms, and the algorithms that potentiate continuous flow of misinformation, may also have played a role.

It is understandable that those who have suffered discrimination, oppression or racism from authorities in the past will be much more likely to suspect it will happen again. Interestingly, even some people who have not suffered discrimination have struggled with taking advice to get vaccine ‘boosted’ from politicians who have been mendacious over other matters. We need to understand how much more difficult it is for those people to trust healthcare professionals, especially those who have experienced recent or past intergenerational trauma from authority figures.

Recent research confirms that people are much more likely to be vaccinated if other people like them are vaccinated too. Evolutionary science also describes how it has been critically important in our evolutionary past to not be ostracised from our in-group, as that would have meant certain death. We are therefore adapted to fit in with our family and friends and find it very difficult to go against what they advise.^{Reference Salali and Uysal16} This is especially relevant (and problematic) if our friends are against accepting the vaccine.

Lastly, evolutionary theory informs us about ‘trade-offs’: as life is rarely easy, we need to weigh up the risks and benefits to make decisions. These are mostly unconscious. We are the descendants of a long unbroken line of ancestors who survived and reproduced, and we have evolved to prioritise our own survival and that of our offspring.^{Reference Arnot, Brandl, Campbell, Chen, Du and Dyble10} Therefore, we are vulnerable to cognitive biases if the information we are provided with does not match what we feel we need to achieve these aims (Box 1).

Where psychiatric skills can help

Psychiatrists are experts at diagnosing and managing mental disorder. In terms of vaccine refusal, it is very rare that overt psychopathology is the primary cause. One study demonstrated that some psychiatric patients have higher rates of vaccine refusal than the general population, especially those with PTSD, anxiety disorders and substance use disorders.^{Reference Eyllon, Dang, Barnes, Buresh, Peloquin and Hogan18} However, another study demonstrated that vaccine hesitancy in psychiatric in-patients mapped more clearly on to educational and ethnic characteristics.^{Reference Uvais19}

The definition of a delusion requires that the belief is not one ordinarily accepted by other members of the person's culture or subculture and is particularly self-referential, which clearly does not apply to general vaccine refusal. Consequently, the main role for a psychiatrist should be in terms of applying legislation such as the Mental Capacity Act 2005 in England and Wales, designed for patients who have a disturbance of the mind or brain. Patients are thereby evaluated on their ability to understand, retain and weigh up the risks and benefits and communicate their decision. It is nevertheless important to remember that people are allowed to make unwise decisions.

The role of a psychiatrist must not lie in inappropriately forcing people to do something they do not want to do. The Mental Health Act 1983 clearly does not apply to people who simply refuse vaccines. What psychiatrists as doctors can do, though, is to help understand the patient's reluctance and to educate and persuade them to move in the direction that is in their best interests. Psychiatrists are also well placed to explore past experiences that could cause mistrust of the healthcare system, and other reasons for hesitancy, including needle phobia. As psychiatrists we need to be mindful, at least in theory, that some patients who have been forced to have injected medication (for example during rapid tranquillisation or depot antipsychotic medication) may have complex transference responses which may lead to our involvement being unintentionally counterproductive when we recommend vaccination.

Problems that require a political solution

We have so far focused on the individual. However, it is clear that there are international forces at work that have a great influence on individuals that may surpass the effects of their in-group of family and friends. People who are ideologically motivated to be against vaccines are called anti-vaxxers. The anti-vaxxers are partly driven by people who are economically motivated by selling ineffective preparations that supposedly protect against COVID-19 or hasten recovery, or who earn substantial sums from social media sites through the traffic they attract to their sites.^{Reference Watts17} There are also anti-vaxxers who are politically motivated and who aim to destabilise countries and governments. A recent investigation showed that those spreading misinformation are ‘well financed, determined and disciplined’ and ‘actively working to sow doubts about the deadliness of COVID-19, vaccines and medical professionals’ integrity’.^{Reference Ahmed20} Manipulating people for political or economic gain is a part of international big business and is poorly regulated in online services. Scams and disinformation need to be combatted at a national level.

In the USA, political affiliation is also a major determinant of one's stance on vaccines, even stronger than ethnicity or socioeconomic status. A polarised political landscape may have contributed to extreme decisions that would not be possible in other circumstances.^{Reference Galston21}

Recommendations for practice

It is easier to blame an individual than to consider complex systemic effects – this is as true for obesity and child maltreatment as it is for people who refuse to accept the COVID-19 vaccine. Unfortunately, the natural protective effect that distrust in authority holds for people who have reason to feel that way can be co-opted and amplified by others who seek financial and/or political gain by exploiting that distrust.

As vaccine hesitancy is a complex, multifaceted problem, a one-size-fits-all solution will not be effective. Strategies that have been shown to increase vaccine uptake are:^{22,Reference Panchal and Jack23}

• • listening to the individual and taking their concerns seriously and using motivational interviewing skills to help

• • not engaging with misinformation online, as that can increase traffic and amplify it

• • sharing good-quality information from organisations that are above distrusted authority figures, for example from the World Health Organization²⁴ rather from than the national government

• • encouraging scientists, faith leaders and healthcare professionals to share that they are vaccinated and that it is safe and to support others from their social and/or ethnic background to be able to do the same

• • avoiding the imposition of mandatory vaccination programmes that may increase uptake in the short-term, but may cause a serious backlash against all vaccines in the longer term.^{Reference Haviari, Bénet, Saadatian-Elahi, André, Loulergue and Vanhems25}

About the authors

Annie Swanepoel is a consultant child and adolescent psychiatrist working in Southend, Essex and Thurrock Children's and Adolescent's Mental Health Service (SET CAMHS), North East London NHS Foundation Trust (NELFT), Chelmsford, UK. Riadh Abed is a retired consultant general adult psychiatrist living in Sheffield, UK. Muzaffer Kaser is a consultant general adult and liaison psychiatrist working in Cambridgeshire and Peterborough NHS Foundation Trust and in the Department of Psychiatry at the University of Cambridge, UK. Paul St John Smith is a retired consultant general adult psychiatrist living in St Albans, UK.