Skepticism and anxiety are as old as vaccines themselves.

It’s not a problem that can be brushed off. There’s little hope of life returning to normal, much less of conquering a virus that has killed 2.7 million and paralyzed economies worldwide, until enough people step up to achieve herd immunity: probably upward of 70%. Even a small shortfall could be enough to cost lives and livelihoods.

The good news is that experience has taught us plenty about campaigns and resistance. Plus, while COVID-19 has been a catastrophe, it’s also an unprecedented opportunity, given the visible public health ravages, to change minds and prove the value of vaccines.

The less positive news is that the causes of skepticism are manifold and complex. Misinformation is one problem: We know that from episodes such as the Nigeria polio vaccine boycott in 2003-2004, or the scare around the diphtheria, pertussis and tetanus vaccination in the 1970s and 1980s.

A Facebook study showed a small subset of users was responsible for most of the skeptical content posted. But there are plenty more sources, from lack of trust in authorities to health care barriers to simple racism. Episodes like the 40-year Tuskegee syphilis study that denied Black men in Alabama diagnosis and treatment cast a long shadow.

It’s a far lengthier list for COVID-19, where disinformation was present from the start, fed by geopolitical tensions and polarized domestic agendas.

The swift appearance of vaccines unsettled even more people, unclear where time was saved or how risks balance against rewards. Europe’s suspension of AstraZeneca’s COVID-19 vaccine over reports of blood clotting may be understandable as a show of caution, but real-world evidence suggests the shots are safe. Once sown, doubts are very hard to clear.

In a way, it’s odd that vaccines spark so much debate. Far fewer people feel so strongly about allergy medication or cough syrup. Heidi Larson, who runs the Vaccine Confidence Project at the London School of Hygiene and Tropical Medicine and studies rumors, connects it to the involvement of government and big business: institutions in which distrust runs high.

In a recent address, she said it’s less an information problem than a relationship one. Low faith in authorities means few will take risks.

It’s clearly necessary to block anti-vaccine disinformation on social media platforms, but it’s not a solution on its own, any more than mandating the injection: a move that would further antagonize and polarize, damaging future efforts. Simply shutting down skeptics is a poor tactic when exclusion is half the problem.

Pictures of vaccinated celebrities, simple booking mechanisms and basic access to injections are all important.

But it’s vital to listen to the doubters and understand where the problems are coming from.

One option is what one U.S. public health specialist described to me: Focus groups that connect peers and seek to answer questions and educate without preaching. His experience among Hispanic and other communities suggests naysayers are brought around after evidence from a friend or relative, or when an acquaintance has been vaccinated without adverse consequences.

Community discussions won’t fix deep-seated distrust in government and may not reconcile everyone with science. It’s late, and the push should have started months ago. But we can still reach enough people to make a difference.

Clara Ferreira Marques is a Bloomberg Opinion columnist covering commodities and environmental, social and governance issues.