Why people reject vaccination — and how to change their minds

As of early December, about 8.5 billion doses of Covid-19 vaccine have been administered worldwide. That makes the Covid-19 vaccination effort easily the largest public health intervention in history — and yet, its success has been mixed. 

The world's most vulnerable countries have been denied their fair share of vaccination doses, while in wealthier countries, the main problem is not access but hesitancy, often concentrated in specific regions of anti-vaccination sentiment. 

For example, the eastern German state of Saxony has full vaccination rates of only around 56%, and an infection rate more than twice as high as the country as a whole.

Much of the discussion around Covid-19 vaccine hesitancy has focused on how different the Covid-19 vaccine is from other vaccines — for example, no other vaccine has been developed as quickly. But to view Covid-19 vaccine hesitancy as a new phenomenon neglects the meteoric rise of broader anti-vaccination sentiment worldwide over the last few decades. 

There may be no better illustration of this concept than the measles vaccine. As an extraordinarily contagious disease, measles requires a vaccination rate of around 95% to achieve herd immunity—the point at which the disease won't circulate through the population freely. 

In 1978, after the year before the first dose of the measles vaccine was introduced in Romania, 540 out of every 100,000 people contracted measles. By the turn of the millennium, child vaccinations had hit 96% and incidence in Romania had reduced to 0.16 per 100,000 people—a tremendous accomplishment by any standard.

But then measles vaccination rates began to fall. By 2017, they were down to 86% of the population for the first dose, 75% for the second, and Romania was embroiled in a years-long epidemic, along with much of Europe. In 2018, there were 83,540 cases of measles across Europe, compared to 5,273 just two years before.

In cases like Romania's, when a country has initially high rates of vaccination that then decline, vaccine access is not the issue; instead, vaccine hesitancy is the culprit. For example, Italy also suffered outbreaks of the measles in 2017-19 due to a similar lapse in vaccine uptake. 

The demographic patterns of the cases in such outbreaks emphasise the role of vaccine hesitancy: 78% of the cases in a 2013 measles outbreak in New York were children unvaccinated due to parental refusal or intentional delay.

Vaccine hesitancy might seem like a niche behaviour—some research suggests only 8% of Americans reliably identify themselves as "anti-vaxxers"—but it is a well-established issue in public health, and it is here to stay. 

Nearly a year before Covid-19 first emerged, the World Health Organisation identified vaccine hesitancy as one of the top ten threats to global health. Eradicating disease will not be possible until we understand the complex psychological and cultural reasons that underlie anti-vaccination attitudes. 

Let us start with the psychological part. Vaccination is psychologically counterintuitive. Human behaviour is strongly motivated by rewards — specifically, immediate and tangible rewards, which trigger powerful emotional reactions. 

When the instant pleasures of junk food face off against the subtle, long-term rewards of a nutritious diet, healthy eating rarely wins out. This calculus does vaccination no favours. A successful vaccination experience is characterised by not getting sick—a non-event that is difficult to even perceive, let alone appreciate as a reward.

In addition, vaccination's reputation suffers from the psychological phenomenon known as omission bias: people see the harm caused by action (such as side effects of getting vaccinated) as more severe and meaningful than the harm caused by inaction (such as becoming ill after not getting vaccinated). 

Perhaps worst of all, vaccines can become victims of their own success. When vaccination rates increase, disease rates drop. Generations who grew up without exposure to diseases such as measles have little reason to fear their consequences. When misinformation about the risks of vaccines meets ignorance about the risks of disease, vaccination rates drop.

Until the next outbreak, that is. In 2018, Romania's measles vaccination rate rebounded to 81% for the full two doses, an example of the upticks that often occur when the consequences of being unvaccinated become visible.

But anti-vaccination attitudes are not only about what happens inside our heads; they are also in constant conversation with our social and cultural environment. 

Motivations to vaccinate are very culturally specific. Many anti-science beliefs can be best understood as the product of certain attitude roots, or psychological motivations that keep people from changing their minds even in the face of contradicting evidence. In fact, among individuals who are the most committed to anti-vaccination beliefs, correcting myths about vaccination only increases skepticism.

To overcome vaccine hesitancy, we must unearth these roots and determine what the act of vaccination means to people—something that does not always generalise across cultural contexts.

In the US, for example, anti-vaccination beliefs are often a function of conspiratorial ideation or Republican political affiliation. Conspiracy theories appeal to believers for many reasons—for one, they can help people feel intelligent for seeing through society's lies. 

The reasons why Republican political affiliation has become linked to anti-vaccination beliefs are more complex, but statements by influential figures such as former US President Donald Trump, who encouraged getting the Covid-19 vaccine while in office but both before and after his presidency expressed doubt about vaccines, have contributed to making anti-vaccination attitudes a mainstream belief among American conservatives.

Our research team at Duke University's Center for Advanced Hindsight investigates novel solutions to increase vaccine uptake. In the case of measles vaccination, we decided to focus on the self-protective angle of conspiracy theories. If believing they are in on a secret helps conspiratorial thinkers affirm their self-worth as intelligent people, what happens if we meet that need in a different way?

In 2019, we recruited 1,087 pregnant mothers from the US to tell us about a time they felt intelligent, a time they felt like good parents, a time they felt like bad parents, or to complete an unrelated task. We then had them read a persuasive passage arguing in favour of the measles vaccination. 

Last, we asked about their intentions to vaccinate their future child. Our major interest was in the intelligence prompt, because we wanted to see if we could offer our participants a chance to affirm their self-worth in a healthier way.

The answers we got in response to our intelligence prompt were mostly small moments, spelled out in a sentence or two. Women told us about adapting quickly to new jobs, succeeding at math classes or tests, solving problems for their loved ones, winning arguments with coworkers, innovating at work or impressing a supervisor. 

But despite the brevity of the answers, those who wrote about feeling smart were significantly more likely to agree they would vaccinate their child. 

Why? They found the pro-vaccination passage more persuasive than those who'd written about anything else. Once their psychological need to feel intelligent was met through another source, they could accept the science and consider vaccination as an option. Their vaccine hesitancy had nothing to do with ignorance—and everything to do with what anti-vaccination attitudes mean for someone in the United States. 

More recently, our team has turned our attention to Covid-19 vaccination. This spring, we studied the effects of different pro-vaccination messages on Covid-19 vaccine intentions by surveying a racially representative sample of 1,748 people from the southeastern US. 

We showed our participants one of six different messaging strategies, ranging from framing the vaccine as the route back to normal life to explaining the US Food and Drug Administration's testing process, then asked about their attitude toward the Covid-19 vaccine.

Only two of our approaches worked to increase vaccination intention. The first successful message focused on combating omission bias by emphasising the risks of not vaccinating as far greater than the risks of vaccination.

The second successful message was a little more unusual. We framed Covid-19 vaccination as a patriotic act—a way for people to help the US rise to meet the challenge of Covid-19. 

The idea for this intervention sprang directly from a consideration of what motivates anti-Covid-19 vaccination attitudes in US culture. Trump's historical anti-vaccine statements and remarks subsequent to his presidency contributed to creating an environment where to be pro-vaccine was to be anti-Republican—and in the US, political party affiliation is a stronger identity than even race or religion. 

By tying vaccination to patriotism, another cherished value, this intervention allowed readers to sidestep the uncomfortable tension between Republican identity and vaccination behavior. In fact, our patriotism-themed message was especially successful among Republican participants, nearly erasing the gap between political parties.

But what worked in the US will not necessarily work elsewhere. Omission bias may be universal, but other motivating factors behind anti-vaccination attitudes do not look the same from country to country. 

For example, in 2003, several primarily Muslim states in northern Nigeria boycotted the polio vaccine due to concerns that it could spread HIV and cause sterility. 

These concerns were a result of many complex factors, including fears of an anti-Islam US crusade spurred on by the US' response to Sept. 11, and the memory of Pfizer's deadly anti-meningitis drug trials in Nigeria in 1996. 

Kano, the last Nigerian state to uphold the boycott, lifted it after ten months, only when it received vaccines manufactured in Indonesia—a predominantly Muslim country. There could perhaps be no clearer example of a culturally sensitive solution.

A similar lens must be applied to Covid-19 vaccination.

Experts in the social sciences across the globe must work together to identify the roots that underlie vaccine hesitancy and understand how these factors differ across communities at both national and local levels.

We can then move beyond information and education to target hotspots of hesitancy, either by addressing the psychological needs that anti-vaccination serves or by framing vaccination as part and parcel of important cultural values. 

Whichever paths we choose, one thing is clear: We will not succeed at protecting ourselves and our loved ones against Covid-19 until we understand vaccine hesitancy as an emotional, social, and cultural problem, and apply tailored solutions accordingly.

Jenna Clark is a senior behavioural researcher at Duke University's Center for Advanced Hindsight, where she specialises in applied behavioural science work to encourage preventative health behaviours.

Disclaimer: This article first appeared on Foreign Policy, and is edited and published by special syndication arrangement.