It started with a trip to the Philippines. When the travelers returned to Ohio in March of this year, they brought back a tiny but destructive souvenir, one of the most infectious human viruses on earth. The travelers hadn’t been immunized with the measles-mumps-rubella (MMR) vaccine and had become infected with measles. Their one trip ended up setting off the largest outbreak of the illness the U.S. had seen in more than a decade. By the end of May, U.S. measles cases were the highest they had been since the disease was eliminated from the country 14 years ago. (Elimination means the disease is no longer circulating on its own in the country but can still be brought in from the outside.) At time of publication, the count from this year’s imported cases has reached almost 600 across 21 states. Still, the U.S. has been better off than the U.K., where more than 1,300 cases in 2008 forced Britain’s Health Protection Agency to announce that measles was now endemic in that country again, after having been eliminated in 1994. “Due to almost 10 years of sub-optimal MMR vaccination coverage across the UK, the number of children susceptible to measles is now sufficient to support the continuous spread of measles,” stated the HPA that year. Last year, confirmed cases in the U.K. surpassed 1,800 despite MMR vaccination rates finally returning last year to the levels they had been before 1998.

Today, both counties are now seeing more measles cases than at any other time since 1998.

It was the events of 1998 that helped both the U.S. and the U.K. end up where they are today, fighting to contain outbreaks of a vaccine-preventable disease both countries had already exiled once before. A now-disgraced surgeon by the name of Andrew Wakefield held a press conference where he presented fraudulent findings claiming that the MMR vaccine caused autism. While other factors would play a lesser role, that single press conference had the same effect as flipping the wrong railroad switch, facilitating the train wreck—the return of measles—that would occur in both countries several years later. The effect in the U.K. was quickly apparent. In just five years after the press conference, vaccination rates had dropped to 80%. A similar trend would play out in pockets of the U.S. a few years later. Today, both counties are now seeing more measles cases than at any other time since 1998, and it’s not clear if the numbers have reached their peak or if they will continue climbing. In the U.K., at least, there’s reason to hope that measles cases will begin to decline. In the last year, England’s vaccination rates for measles passed 92% for young children, part of a continuing upward trend, and rates in Scotland and Northern Ireland are above 95%. The British government has pushed hard to recover from the drop off in the late 1990s and early 2000s and meet the 95% target that ensures population-level protection. Meanwhile, in the U.S., rates have stubbornly hovered around 91% and, in some regions, are substantially lower. In both countries, the persistent anti-vaccination movement remains a threat, which has public health officials on both sides of the pond looking to their counterparts: How can they successfully address low immunization rates and tame the now-persistent measles outbreaks? Setting the Stage Measles was one of the top killers among infectious diseases worldwide until a vaccine was developed in 1963. Even as recently as 1980, before global vaccination efforts began in earnest, an estimated 2.6 million children worldwide died from measles each year. It is also one of the most contagious of vaccine-preventable diseases: Nine out of ten people exposed to it will become ill without immunity from a vaccine or a prior infection, and each case yields 15 to 20 more in a non-immune population. After the U.K. and the U.S. introduced the vaccine, cases plummeted. One dose provides 95% protection against the disease; the second boosts that to 98-99%. Such an effective vaccine was one reason the World Health Organization has chosen measles as the next disease slated for worldwide eradication, to follow in the footsteps of smallpox and, if successful, the current polio eradication campaign. Not all diseases can be eradicated; to be a candidate, there must be an effective way to stop transmission of the disease (such as a vaccine), it must be a disease we can accurately diagnose, and it must only afflict humans. Because of the existence of an effective vaccine, the World Health Organization chose measles as the next disease slated for worldwide eradication. When the campaign was rolled out by the WHO in 1998 , one of the first steps toward worldwide elimination by 2015 was the elimination of measles from Europe by 2010. The announcement occurred the same year that Wakefield published a fraudulent, now-retracted study in the prestigious British medical journal The Lancet that claimed a link between the MMR vaccine, autism, and gastrointestinal problems. On February 26 at the Royal Free Hospital in London, Wakefield spoke off-script from what he and his fellow authors had arranged before the press conference. Based only on a case series of 12 children—with data later shown by journalist Brian Deer to have been doctored—Wakefield expressed doubts about the safety of the MMR vaccine. The year before, MMR coverage in England stood at 91 percent—better than the 88.5% in the U.S.—but by the end of that year, English MMR rates had dipped below 90% for the first time in seven years. But Wakefield had not come out of nowhere. “Everyone believes that the Wakefield trouble all started with the Lancet paper but this just isn’t true,” says David Salisbury, former Director of Immunization at the U.K. Department of Health. “He had already published a series of papers trying to link measles virus with inflammatory bowel disease, then measles vaccine with IBD, and we already knew that his research findings could not be trusted.” Nevertheless, it was after the publicity of the Lancet paper that MMR coverage began dropping. The trend continued for more than a decade, hitting a low of 80% in 2003, the same year as the first big outbreak since measles elimination in the country.

Fears about vaccines in general go as far back as Edward Jenner’s first vaccine against smallpox in 1796

The hysteria over a possible MMR-autism link took longer to reach the U.S. and never achieved the same heights as in the U.K. But it certainly left an impact, adding fuel to a vaccines-autism fire on this side of the Atlantic. To grasp how Wakefield’s study could have such reverberations in both countries—especially when dozens of subsequent studies showed no link between autism and MMR or any other vaccine—it’s important to understand the history of vaccine concerns. In a way, Wakefield’s paper was just history repeating itself. Fears about vaccines in general go as far back as Edward Jenner’s first vaccine against smallpox in 1796, but the most recent eruption of such fears in the U.K. had been just two decades earlier, centering on the diphtheria-tetanus-pertussis (DTP) vaccine. Pediatric neurologist John Wilson, of The Hospital for Sick Children in London, published a paper in 1974 claiming that 36 children had suffered severe neurological complications from the DTP vaccine. The pertussis vaccine used the whole cell of the bacterium, which could lead to high fevers sometimes resulting in seizures in children, but these febrile seizures did not cause any long-term damage. Still, media reports perpetuated the fears, and the resulting drop in DTP immunizations—from 80% to 31% in four years—led to several whooping cough (pertussis) epidemics and dozens of infant deaths. “Study after study showed that [Wilson’s] study was wrong,” says Paul Offit, chief of the division of infectious diseases at Children’s Hospital of Philadelphia. “But [the U.K.] exported that fear, the notion that the whole cell vaccine caused encephalopathy.” Soon enough, concerns about the DTP vaccine crossed the ocean and arrived in the U.S., leading to litigation against pharmaceutical companies. When an acellular pertussis vaccine became available, the U.S. switched to it in the mid-1990s. By then, pertussis immunization rates in the U.K. had recovered, but the U.K. was in the midst of a different public health scare, a legitimate one surrounding bovine spongiform encephalopathy (BSE), or mad cow disease, in the country’s beef products—just two years before Wakefield’s press conference. By the time the Wakefield press conference did happen, says Heidi Larson, a senior lecturer at the London School of Hygiene and Tropical Medicine, “There was mistrust of the public health officials partly due to loss of trust during the management of the ‘mad cow’ BSE saga, where the public health officials were not transparent and played down the scale of the problem.” As the MMR-autism scare gained momentum in the U.K., public wariness increased when, in 2001, Prime Minister Tony Blair refused to say whether his son had received the MMR vaccine, citing privacy concerns. Although it was later revealed that his son had been vaccinated, the family’s initial refusal to say only exacerbated public mistrust. Meanwhile, concerns in the U.S. had been centering on a vaccine preservative called thimerosal, which some believed might cause autism. Although those concerns were also unfounded, the preservative was removed from all childhood vaccines in 2000, both the year measles had been declared eliminated in the U.S. and the year Wakefield appeared in U.S. media for the first time, in a story buried on page 20 in the New York Times about Congressional hearings being held to look into the MMR-autism link. Six months later, Wakefield was on 60 Minutes , and U.S. coverage of the controversy took off. Managing the Crises Fueled by sensationalist media coverage, fears about an MMR-autism link had left the U.K. well below the 95% coverage needed for herd immunity protection from measles. Measles cases soon began climbing in the small country. By 2002, immunization levels in London were at 73%, and an outbreak led to hundreds of cases. Health officials were already springing into action. “We realized that the worst thing was to try to engage with Wakefield and his allies as we were put into indefensible positions and misrepresented,” Salisbury says. “We also realized that the best redress was by using local health providers as our advocates with parents as we knew they were trusted by families. When the local health professionals were resolute, parents trusted their advice. If they wavered, it was too easy for parents to shun MMR.” MMR rates slowly began recovering, but that could not reverse the damage done. “The new kids being born get vaccinated and the coverage goes back up, but you have these cohorts of children who were not vaccinated before who are still susceptible,” says Dan Salmon, deputy director for the Institute for Vaccine Safety at Johns Hopkins Bloomberg School of Public Health. “That’s why you’re seeing all these outbreaks now.”

“The U.S. hasn’t seen the drastic drops in coverage that the U.K. saw, and I believe this is at least partially due to immunization laws.”

Outbreaks in the U.K. began really climbing in 2006, just as those cohorts of unvaccinated children were entering school. Most years since 2008, England and Wales have seen at least 1,000 cases annually. In April 2013, England began a national Catch-Up Programme to identify and vaccinate the children who had not received the MMR during the height of the scare. The U.S., meanwhile, saw only a tiny, brief drop in MMR coverage in 2000, when the percentage of children not getting the MMR vaccine jumped barely two percentage points, but that was before U.S. media coverage of the controversy had taken off. Authors of a 2008 paper looking at nonreceipt of the MMR suggested the jump could have resulted from parents hearing of the controversy from other sources, such as online, or from health care providers who became hesitant to administer the vaccine. But another factor played a protective role: “To some extent, daycare-entry and school-entry requirements may have preserved MMR coverage in this country,” those authors wrote . “We haven’t seen the drastic drops in coverage that the U.K. saw, and I believe this is at least partially due to immunization laws,” says Saad Omer, associate professor of global health at Emory University. He says people outside the U.S. often see these laws as “draconian” because they misunderstand how they work. “In reality, these laws change the balance of convenience from non-vaccination to vaccination,” Omer says. “The basis of these laws is in the police powers of the state, predating the Constitution. States can compel people to do a few things that are in the overall interest of society, and these have provided a buffer against drastic drops in coverage.” In most states, however, public school students can seek exemptions from the requirements for religious or philosophical reasons—the U.S.’s Achilles’ heel. Over the past 14 years, while the Vaccines for Children program was increasing access to vaccines for lower-income children, non-medical exemptions were increasing, so MMR vaccination rates never budged from the low 90s. “It’s hard to separate out the difference between what would have gone up because of improvements in administering immunizations and the impact of exemptions and people delaying vaccines,” Salmon says. “It’s clear we have more parents refusing vaccines for their children in states with exemptions. Maybe we would have seen an increase in coverage if [the MMR controversy] hadn’t held us back.” The problem with exemptions, as Omer’s research has found throughout the country, is that they tend to cluster together geographically, and those clusters have been associated with larger outbreaks of vaccine-preventable diseases. In 2012, Omer published findings in the New England Journal of Medicine showing that non-medical immunization exemptions have “continued to increase, and the rate of increase has accelerated” between 2005 and 2011. Another of his studies found exemptions among California kindergarteners steadily increased over 16 years. “It’s all a local issue. If coverage in your community is really bad, then you’re not helped a whole lot by the state and national coverage,” Salmon says. “The disease doesn’t care why people are susceptible. Disease has a way of finding those pockets.”

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Moving Forward Although the U.S. never saw the big drops in MMR coverage and large outbreaks the U.K. experienced, U.S. public health officials can still learn from the U.K., especially in terms of data collection. MMR coverage rates in the U.S. might actually be higher than reported, but it’s currently impossible to know because the National Immunization Survey only collects information on individual vaccines through 35 months of age, and some parents delay the vaccine until after age 3. While NIS surveys include a large sample—about 30,000 children—they still represent only general state and national levels and are unable to detect local clusters of unvaccinated children. State reporting of non-medical exemptions can often reveal those clusters, but that information comes from schools, so data quality varies, and using exemption numbers as proxies for immunization coverage is unreliable. Some children, for example, will be listed as “unvaccinated” even if they have received their MMR vaccine because they may have missed a different shot. “A lot of exemptions are picking and choosing,” Salmon says. “The schools don’t usually collect what vaccines children were exempt for. They just report that kids have an exemption.”

“Nation-wide routine ‘listening’ to the public through polling could identify where confidence issues are occurring.”

Thanks to a national health care system, the U.K. has a record of every child’s immunization status for each vaccine, providing far more detailed information about possible clusters of unvaccinated children. Even better, England conducts regular polls on attitudes toward vaccines. “The Department of Health started biannual polling of public sentiments about vaccines to better understand the nature and scope of concerns and where they were most prominent so that they could tailor and target their communication and trust building,” Larson says. “The nation-wide routine ‘listening’ to the public through polling [in the U.S.] could identify where confidence issues are occurring before they turn into refusals and disease outbreaks.” U.S. researchers do study parent concerns, but coverage is sporadic and methodologies vary. There is no ongoing nationwide surveillance as there is in the UK, even though such information might help provide “a warning before a drop in coverage,” Salmon says. Salisbury attributes the recovery of the U.K.’s MMR rates in part to a health care system in which all children receive scheduled invitations from their primary care providers to come for their vaccines at specific times on specific days at specific places. These are not unlike well-child visits in the U.S., except that not all pediatricians necessarily send reminders to parents, and parents must first choose a pediatrician and make the initial appointment. Once parents do choose a particular doctor, however, research shows those doctors play a major role in parents’ vaccination decisions.

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The problem is having sufficient time at visits, says Douglas Opel, an assistant professor of pediatrics at the University of Washington School of Medicine who has researched vaccine hesitancy. “One of the major barriers to vaccine acceptance, especially among vaccine-hesitant parents, is our inability as providers to adequately address their concerns, and that begins with having the time to do so,” Opel says. The typical 20-minute well-child visit covers recommended vaccines, a physical exam, and discussions of development, nutrition, behavior, and safety. “It really throws a wrench into how adequately you can address those concerns given those competing demands,” he says. Where the U.S. has an advantage over the U.K., again, is in legislation requiring vaccines for school. Here, individual states have more ability to improve immunization rates than the federal government does. Omer’s research has shown that more stringent requirements for exemptions result in lower non-medical exemption rates, and with whooping cough cases soaring and measles back in the headlines, states such as California, Vermont and Washington have been tightening requirements. Although his data have shown increasing non-medical exemptions, it’s unclear whether that trend will continue. “You can’t say which direction the rates will go,” Omer says. “We’ll have to revisit the data in a few years.” In the meantime, Omer sees another challenge for both the U.S. and the U.K. that is mostly beyond the control of public officials in either nation: that vaccines’ success is their greatest enemy. “When you haven’t eradicated vaccine-preventable diseases but they are no longer very visible, parents don’t have experience with the disease,” he says. “The risk-benefit calculus changes in their minds, in a milieu of real or perceived adverse events in the absence of the disease.” And therein lay the rub. “The disease incidence is low not because of a miracle,” Omer says, “but because of high vaccination coverage.”

Photo credit: © Valentin Flauraud/Reuters/Corbis