Should governments compel their citizens to receive vaccinations? It's a question that's more pertinent than ever in the wake of the coronavirus pandemic, but a new study suggests that forcing people into getting jabs could become counter-productive.

The research looked at surveys completed by 2,653 German residents during both the first and the second waves of the pandemic, analyzing how attitudes changed over time during 2020. The German government has committed to keeping vaccines voluntary for its population.

Despite infection rates being 15 times higher in Germany during the second wave in October and November, the data showed that resistance to mandatory vaccinations had increased from the first wave in April and May.

Participants were asked how likely they were to get vaccinated, based on whether the vaccinations were enforced by law or voluntary: During both waves, people were more likely to want to get vaccinated if they didn't have to, but the gap was bigger the second time around.

"Costly errors may be avoided if policymakers reflect carefully on the costs of enforcement," says economist Samuel Bowles from the Santa Fe Institute.

"These could not only increase opposition to vaccination, but also heighten social conflict by further alienating citizens from the government or scientific and medical elites."

The researchers also looked at some of the predictors for agreeing to be vaccinated, and trust in public institutions was a big one. Doubts about the effectiveness of vaccines and opposition to personal freedom restrictions were also closely linked.

There's something else going on as well though, the team behind the study suggests: When vaccines are voluntary, more people are persuaded to take them as they see friends and family getting jabbed. When vaccines are mandatory, that ripple effect is reduced.

This ripple effect is similar to the spread of new technologies – like TVs and washing machines when they were first introduced – as more and more people get them, more and more people want the same thing as others who are already enjoying the benefits.

The researchers also posit that forcing people to have jabs takes away their agency to do good (very important in convincing healthy people to get vaccinated), comes across as overly controlling, and reduces trust in the vaccine – because if the vaccine was safe and effective, why would enforcement be needed?

"How people feel about getting vaccinated will be affected by enforcement in two ways – it could crowd out pro-vaccine feelings, and reduce the positive effect of conformism if vaccination is voluntary," says psychologist and behavioral economist Katrin Schmelz, from the University of Konstanz in Germany.

Schmelz and Bowles acknowledge that mandatory vaccines may have to play a part in certain countries and in certain situations – if vaccination rates are particularly low, for example – but they say that the approach should be used with caution.

With countries and organizations now starting to introduce guidelines around vaccinations for attending events or courses, or for traveling to specific places, it's becoming more important than ever to understand the various reasons that can lead to vaccine hesitancy.

The findings here can be useful in any scenario where leaders want to change the minds of their people – from promoting low-carbon lifestyles to increasing tolerance among communities. Sometimes a softer approach is better.

"Our findings have broad policy applicability beyond COVID-19," says Schmelz. "There are many cases in which voluntary citizen compliance to a policy is essential because state enforcement capacities are limited, and because results may depend on the ways that the policies themselves alter citizens' beliefs and preferences."

The research has been published in PNAS.