Public trust is critical when it comes to vaccines. When people lose their confidence in immunizations and see them as useless, unhelpful, or downright harmful, they are less likely to get the lifesaving shots. And when people don’t get their immunizations, terrible, vaccine-preventable diseases like measles or whooping cough are more likely to flare up.

In a new study, published in EBioMedicine, researchers at the London School of Hygiene & Tropical Medicine, Imperial College London, and the Saw Swee Hock School of Public Health in Singapore tried to measure vaccine confidence around the world. In the largest survey on the subject ever conducted, they asked 66,000 people in 67 countries about their views on the importance, safety, and effectiveness of vaccines.

The aim was simple: To take the global temperature on vaccine sentiment and identify which countries might be at risk of "vaccine confidence crises" and, therefore, outbreaks.

Their findings are striking. Some of the poorest countries and regions of the world had the most trust in vaccine safety, while wealthy Europeans — who also have some of the best access to immunizations — fared terribly.

Regions of the world ranked by their trust in vaccine safety (from most to least):

Southeast Asian region

African region

American region

Eastern Mediterranean region

Western Pacific region

European region

Countries most confident in vaccine safety

Bangladesh (fewer than 1 percent of people surveyed disagreed that vaccines are safe)

Saudi Arabia (1 percent)

Argentina (1 percent)

Philippines (2 percent)

Ecuador (3 percent)

Countries least confident in vaccine safety

France (41 percent of people surveyed disagreed that vaccines are safe)

Bosnia & Herzegovina (36 percent)

Russia (28 percent)

Mongolia (27 percent)

Greece (25 percent, tied with Japan and Ukraine)

France had far and away the most science denialists in the survey, with nearly half of respondents (41 percent) disagreeing that vaccines are safe. (The study authors point out that this is more than three times the global average of 12 percent.)

The United States fell somewhere in the middle. Of the 1,000 people in the US surveyed, 14 percent disagreed vaccines were safe and 10 percent disagreed vaccines were effective. Lead study author Heidi Larson thought this average, however, masked some variation in the country.

"I’m pretty confident that if we had done a state-level analysis, we’d have seen more extremes," Larson said, referring to the tremendous variation in vaccine coverage rates within states and counties in the US.

Why does Europe distrust vaccines?

The study didn’t look at the reasons for the discrepancies in vaccine trust, but Larson surmised that there’s probably a link between high-profile vaccine controversies in Europe and diminished trust in vaccines. A number of vaccine scares have taken place in France in recent years — including concerns about whether the hepatitis B vaccine may cause multiple sclerosis, and worries about the safety profile of the HPV vaccine — "none of which have been scientifically [proven], but they’ve created some anxieties," Larson said.

A similar cycle played out in the UK over the past two decades. In 1998, an esteemed medical journal published a paper with a startling conclusion: that the measles, mumps, and rubella vaccine — administered to millions of children across the globe each year — could cause autism.

This study, led by the discredited physician-researcher Andrew Wakefield, has since been thoroughly eviscerated: The Lancet retracted the paper, investigators have described the research as an "elaborate fraud," and Wakefield has lost his medical license. Still, Larson said, "it took five years for [MMR vaccine coverage] to drop to its lowest point after that article, and another 15 years for it to recover to the pre-Lancet days."

Many of the countries with a lot of vaccine denialism are also places with strong beliefs in homeopathic and alternative medicines. "In France, if you go into most pharmacies, they will have a good portion of the store dedicated to homeopathy," Larson says. (There is no reliable evidence that homeopathy is effective.)

By contrast, she thinks the higher trust in vaccines in many poorer countries in Africa and Asia may be attributed to the fact that the diseases vaccines prevent are still common there. "People in these countries have other reasons for being more confident in vaccines," she said. "It’s something they feel there’s some value in for their children’s health, because they face these diseases." There may be less room for denialism in places where people can see the impact of these deadly scourges every day.

Europe has seen massive outbreaks of measles and other vaccine-preventable diseases

France has been battling some of the world’s largest measles outbreaks in recent years, on a scale usually seen in low-income countries like the Democratic Republic of Congo or Somalia. Between January 2008 through December 2011, France reported 22,686 measles cases — an epidemic that has hampered the country’s efforts to eliminate the disease.

France isn’t alone in Europe. There were 2,016 measles cases in England and Wales in 2012 — the most in a year since 1994. Over the past year, Italy reported 617 measles cases, the United Kingdom reported 371, and Germany reported 260. In 2015, Spain experienced an outbreak of whooping cough involving more than 4,800 people.

These numbers make the 2015 Disneyland measles outbreak in California, which involved fewer than 200 people, look small.

Unsurprisingly, researchers have found that rates of whooping cough and measles are higher among people who are intentionally unvaccinated. So there’s a clear link between refusing vaccines and risk of outbreaks.

What to do about this is less clear. Since vaccine exposure and availability don’t seem to predict how people feel about shots, the study authors noted that their research signals a "shift away from access to vaccines as the primary barrier to vaccination in many countries."

This means the public health community needs to work on understanding and addressing all the other barriers that may be preventing people from getting immunized — including the lack of vaccine confidence in some places.

"The public is much more questioning today," Larson said. There’s a limit to how much people will accept the old "take this because it’s good for you" adage, she added. "People are saying, ‘Wait a minute — I want a voice here.’" The trouble is, when it comes to vaccines, waiting can be deadly.