In two essays, “Illness as Metaphor” in 1978 and “AIDS and Its Metaphors” in 1988, the critic Susan Sontag observed that you can learn a lot about a society from the metaphors it uses to describe disease. She also suggested that disease itself can serve as a metaphor—a reflection of the society through which it travels. In other words, the way certain illnesses spread reveals something not just about a nation’s physiological health but also about its cultural and political health. For instance, AIDS would not have ravaged America as fully as it did without institutionalized homophobia, which inclined many Americans to see the disease as retribution for gay sex.

Now another virus is offering insights into the country’s psychic and civic condition. Two decades ago, measles was declared eliminated in the U.S. Yet in the first five months of this year, the Centers for Disease Control and Prevention recorded 1,000 cases—more than occurred from 2000 to 2010.

The straightforward explanation for measles’ return is that fewer Americans are receiving vaccines. Since the turn of the century, the share of American children under the age of 2 who go unvaccinated has quadrupled. But why are a growing number of American parents refusing vaccines—in the process welcoming back a disease that decades ago killed hundreds of people a year and hospitalized close to 50,000?

One answer is that contemporary America suffers from a dangerous lack of historical memory. Most of the parents who are today skipping or delaying their children’s combined measles, mumps, and rubella (MMR) vaccine don’t remember life with measles, much less that it used to kill more children than drowning does today. Nor do they recall how other diseases stamped out by vaccines—most prominently smallpox and polio—took lives and disfigured bodies.

Our amnesia about vaccines is part of a broader forgetting. Prior generations of Americans understood the danger of zero-sum economic nationalism, for instance, because its results remained visible in their lifetimes. When Al Gore debated Ross Perot about NAFTA in 1993, he reminded the Texan businessman of the 1930 Smoot-Hawley Tariff Act, which raised tariffs on 20,000 foreign products—prompting other countries to retaliate, deepening the Great Depression, and helping to elect Adolf Hitler. But fewer and fewer people remember the last global trade war. Similarly, as memories of Nazism fade across Europe and the United States, anti-Semitism is rising. Technology may improve; science may advance. But the fading of lessons that once seemed obvious should give pause to those who believe history naturally bends toward progress.

Declining vaccination rates not only reflect a great forgetting; they also reveal a population that suffers from overconfidence in its own amateur knowledge. In her book Calling the Shots: Why Parents Reject Vaccines, the University of Colorado at Denver’s Jennifer Reich notes that starting in the 1970s, alternative-health movements “repositioned expertise as residing within the individual.” This ethos has grown dramatically in the internet age, so much so that “in arenas as diverse as medicine, mental health, law, education, business, and food, self-help or do-it-yourself movements encourage individuals to reject expert advice or follow it selectively.” Autodidacticism can be valuable. But it’s one thing to Google a food to see whether it’s healthy. It’s quite another to dismiss decades of studies on the benefits of vaccines because you’ve watched a couple of YouTube videos. In an interview, Reich told me that some anti-vaccine activists describe themselves as “researchers,” thus equating their scouring of the internet on behalf of their families with the work of scientists who publish in peer-reviewed journals.

In many ways, the post-1960s emphasis on autonomy and personal choice has been liberating. But it can threaten public health. Considered solely in terms of the benefits to one’s own child, the case for vaccinating against measles may not be obvious. Yes, the vaccine poses little risk to healthy children, but measles isn’t necessarily that dangerous to them either. The problem is that for others in society—such as children with a compromised immune system—measles may be deadly. By vaccinating their own children, and thus ensuring that they don’t spread the disease, parents contribute to the “herd immunity” that protects the vulnerable. But this requires thinking more about the collective and less about one’s own child. And this mentality is growing rarer in an era of what Reich calls “individualist parenting,” in which well-off parents spend “immense time and energy strategizing how to keep their children healthy while often ignoring the larger, harder-to-solve questions around them.”

Historical amnesia and individualism have contributed to a third cultural condition, one that is more obvious but also, perhaps, more central to measles’ return and at least as worrying for society overall: diminished trust in government. For earlier generations of Americans, faith in mass vaccines derived in large part from the campaign to eradicate polio, in the 1950s—a time when the country’s victory in World War II and the subsequent postwar boom had boosted the public’s belief in its leaders. This faith made it easy to convince Americans to accept the polio vaccine, and the vaccine’s success in turn boosted confidence in the officials who protected public health. So popular was the vaccine’s inventor, Jonas Salk, that in 1955 officials in New York offered to throw him a ticker-tape parade.

In the 1960s, the Johnson administration made mass inoculation one component of the ambitious assault on poverty, ignorance, and disease known as the Great Society. In 1964—a year in which 77 percent of Americans told pollsters they trusted government to do the right thing most or all of the time—the surgeon general established a committee to determine how states should administer vaccines. There was little public resistance. By 1968, half the states required children to be vaccinated to attend school, and the rest soon followed.

As Reich details, today’s skepticism of vaccines has its roots in the alternative-medicine and self-help movements of the 1970s, which encouraged people to question established medical authority. This questioning coincided with a post-Watergate, post-Vietnam disillusionment with government that Ronald Reagan exploited when he declared in his 1981 inaugural address that “government is not the solution to our problem; government is the problem.”

As distrust of government has grown, so too has distrust of vaccines. The anti-vaccination movement’s Rosetta stone is a 1998 paper in the British medical journal The Lancet that linked the MMR vaccine to autism. As is well established, the paper was a fraud. Its lead author, the physician Andrew Wakefield, falsified data and received money from lawyers who were suing vaccine makers. The Lancet later retracted the study, and Wakefield lost his medical license. Twenty-one subsequent studies—including a Danish one involving more than 650,000 children—have found no connection between the MMR vaccine and autism.

But with autism rates rising in the United States, Wakefield found followers on the Republican Party’s anti-government fringe. In 2002, Representative Dan Burton, who in the 1990s had repeatedly implied that the Clintons were involved in the death of Deputy White House Counsel Vince Foster, invited the disgraced doctor to testify before his committee. Burton—whose grandson has autism—went on to hold at least 20 hearings, suggesting that government scientists were covering up a link between vaccines and autism.

Burton was a harbinger. After a Republican presidential debate in 2011, one of the candidates, Michele Bachmann, claimed that the HPV vaccine, which protects against cervical cancer, causes mental retardation. While running for president in 2015, Senator Rand Paul—a physician—argued against mandatory vaccinations by asserting that there are “many tragic cases of walking, talking, normal children who wound up with profound mental disorders after vaccines.” And from 2012 to 2014, while Donald Trump was claiming that President Barack Obama hadn’t been born in the United States, he also tweeted more than 30 times about the supposed dangers of vaccines.

Yet it’s not only conservatives who translate their suspicion of government into suspicion of vaccines. Many liberals distrust the large drug companies that both produce vaccines and help fund the Food and Drug Administration, which is supposed to regulate them. The former Green Party presidential candidate Jill Stein has suggested that “widespread distrust” of what she describes as the medical-industrial complex is understandable because “regulatory agencies are routinely packed with corporate lobbyists and CEOs.” The environmental activist Robert F. Kennedy Jr. claims that thimerosal, a preservative formerly used in some vaccines, harms children. Bright-blue counties in Northern California, Washington State, and Oregon have some of the lowest vaccination rates in the country.

Although polls suggest that conservatives are slightly less accepting of vaccines than liberals are, a 2014 study found that distrust of government was correlated with distrust of vaccines among both Republicans and Democrats. Indeed, the best predictor of someone’s view of vaccines is not their political ideology, but their trust in government and their openness to conspiracy theories.

It’s not surprising, therefore, that a plunge in the percentage of Americans who trust Washington to do the right thing most or all of the time—which hovered around 40 percent at the turn of the century and since the 2008 financial crisis has regularly dipped below 20 percent—has coincided with a decline in vaccination rates. In 2001, 0.3 percent of American toddlers had received no vaccinations. By 2017, that figure had jumped more than fourfold. Studies also show a marked uptick in families requesting philosophical exemptions from vaccines, which are permitted in 16 states.

This surge reflects the ease with which conspiracy theories can spread, and not only via social media. Anti-vaccination activists have enjoyed particular success in communities whose cultural isolation makes them easy prey for misinformation. In 2010 and 2011, Wakefield—who now lives in the U.S.—reportedly visited the Somali community in Minnesota three times, and his supporters distributed pamphlets at community events. As of 2014, the local childhood MMR vaccination rate—which had been 92 percent in 2004—had fallen to 42 percent. By 2017, children of Somali descent accounted for a majority of America’s measles cases.

The epicenter of this year’s outbreak has been the ultra-Orthodox Jewish communities in and around New York City. Here too, anti-vaccine activists have run laps around government and media gatekeepers, who have struggled to keep pace with anti-vaccination misinformation. In May, Wakefield addressed an anti-vaccination rally in New York’s heavily ultra-Orthodox Rockland County, and anti-vaccination messages produced by a supporter have been featured on an influential ultra-Orthodox parenting hotline.

This year’s measles outbreak appears to have started with people who traveled to Ukraine, where infection rates are high. Which points to a broader problem: Unvaccinated Americans face a growing risk of infection because vaccination rates are declining in Europe too, for largely the same reasons. Many of Europe’s political insurgents—including the German Green Party on the left, and Marine Le Pen’s National Rally in France and Italy’s Northern League on the right—oppose mandatory vaccinations. And a 2019 study of western-European voting patterns in the European Journal of Public Health found “a highly significant positive association between the percentage of people in a country who voted for populist parties and [the percentage] who believe that vaccines are not important.”

Of course, some skepticism toward official information—including information from the intermeshed corporate, scientific, and governmental establishments that regulate public health—is worthwhile. Neither the drug companies that produce vaccines nor the public-health officials who regulate them are infallible. Even during the campaign against polio, one of America’s great public-health triumphs, a laboratory in California manufactured defective batches of the vaccine, which ended up paralyzing 164 people and killing 10. And some Americans have legitimate concerns about the influence that drug companies wield today over the regulators who are tasked with keeping their vaccines safe. But there’s a crucial difference between wanting to insulate America’s regulators from corporate influence and believing that the CDC, the FDA, the National Academy of Medicine, and the American Academy of Pediatrics are perpetrating a massive conspiracy to maim children.

Given America’s crises of memory, expertise, and institutional trust, one might despairingly conclude that, just as America will never restore its now battered political norms, it will never restore the norm of near-universal vaccination that existed in the late 20th century. But there’s nothing inevitable about this trend. If vaccination rates can fall, they can also rise. The key is determined, deliberate action to turn the tide.

Since conspiracy theorists thrive when government is corrupt and opaque, Americans can rebuild faith in vaccines by making their approval process more independent and transparent. Congress should provide the FDA with enough funding to review vaccines and other drugs in a timely manner without taking Big Pharma’s money. And it should prevent former bureaucrats from going to work for the drug companies they used to regulate.

Stopping measles also requires empowering doctors. A 2011 Washington State law that required parents to talk with a doctor before getting a vaccine exemption reduced exemptions by 40 percent. And a 2012 study by researchers at Emory and Johns Hopkins found that parents who viewed their doctors as reliable sources of information were less likely to search for material about vaccines online. The problem, as Reich told me, is that pediatricians spend less time with patients than they did decades ago. Changing insurance companies’ reimbursement practices to reward doctors for taking the time to reassure patients that vaccines are safe could push vaccination rates back up.

The implications of all of this go far beyond one disease. Although measles may be the most vivid medical manifestation of America’s political and cultural ailments, it won’t be the last. If Americans won’t take expert advice about something as scientifically proven as the benefits of vaccinating their children, what other life-and-death advice will they ignore?