The other day, during a visit to Portland, I hit my head badly enough to need stitches; I went to the ER only to pause, at the door, where an enormous sign asked patients with measles to don a mask. Although I was still bleeding, I considered turning away. I had a seven-month-old at home, who was not yet eligible for his vaccine. Could I carry measles home with me? I didn’t want to know.

It felt strange to have to worry about this in 2019. A century and a half ago infectious disease was the leading cause of death in Americans, but nowadays mortality from infections is dramatically reduced, thanks not only to antibiotics and the sanitary revolution but to the advent of vaccines. These days, the fear of contagion has given way to a fear of contamination, to fears of BPA and PCBs in our cord blood and estrogen and Prozac in our water supply, and of what vaccines can do to developing immune systems.

And so as of 21 March, 15 states had reported measles cases, for a total of 314 confirmed cases so far this year, several of them in Washington state, where I was visiting, and New York state, where I live. CNN reported on 1 April that the number of measles cases in just these first three months of the year already total the second-highest number of cases since 2000, when measles was eradicated. Darla Shine, the wife of Donald Trump’s deputy chief of staff for communications, epitomized a line of thinking shared by many American anti-vaxxers when she called for us to “bring back” childhood diseases because “they keep you healthy & fight cancer”.

Vaccinations have long been a kind of locus of cultural fear, revealing the nature of our fears

It is slightly ironic that vaccinations, the mechanisms that protect our children from the mortal illnesses that once swept them out of their parents’ hands, are now the focus of our fears, while the once-devastating illnesses are themselves seen as somehow reassuring.

But vaccinations have long been a kind of locus of cultural fear, revealing the nature of our fears. Vaccinations, after all, only work if everyone is in it together. You need to have a herd for herd immunity. Our body politic is splintering and fragmenting, and it is reflected in our vaccination rates. To make a herd, you need to believe in the imagined collective: to be concerned not only about yourself, but the others in the polity.

This fear isn’t new, though our particular iteration of it is modern. Although vaccinations were actually folk medicine in their earliest form (farmers knew that milkmaids exposed to cowpox rarely got smallpox), as the writer Eula Biss points out in On Immunity, people have almost always distrusted them. During an 18th-century smallpox epidemic, citizens in France contested their use, leading Voltaire to inveigh that “twenty thousand persons whom the small-pox swept away at Paris in 1723 [c]ould have been alive at this time.”

Our vaccination debate doesn’t map tidily on to national politics – indeed, anti-vaxxers seem to be spread almost equally across political parties. But our divided politics and the anti-vaxxer movement share three things: distrust of authority, divisive cherry-picking of evidence on both sides, and the fundamental erosion of trust among stakeholders. How can we join together to defeat measles when we don’t share a reality?

Given rising levels of distrust across political parties, it is no surprise that we also can’t agree on the social value of immunity, in which my child’s vaccination will help your grandfather live, or my own vaccination will help your infant survive before she is eligible for her own vaccinations.

‘Our body politic is splintering and fragmenting, and it is reflected in our vaccination rates.’ Photograph: Artyom Geodakyan/TASS

In this sense, the debate over vaccination isn’t just about distrust of medicine or a false nostalgia for our “natural” past. It’s also an expression of the limits of American individualism: a natural (if you will) manifestation of a culture that believes realizing one’s own destiny is the apogee of freedom. Our national narrative privileges Thoreau’s prickly but soaring individualism over, say, Jane Addams’s progressive vision of collective service.

Biss points out in On Immunity that data from the Centers for Disease Control, released in 2014, showed that unvaccinated children are more likely “to be white, to have an older married mother with a college education, and to live in a household with an income of $75,000 or more”. By contrast, under-vaccinated children – children who for various reasons are behind on their vaccinations – “are more likely to be black, to have a younger unmarried mother, to have moved across state lines, and to live in poverty”. Not vaccinating, in other words, moves risk from one group to another – and in this sense is another version of the exercising of inequality and privilege that contribute to national divisiveness in the first place. One has the sense from this data that the well-off believe the risks of illness don’t apply to them, and are willing to let it fall on others. (In a way, vaccination is a victim of its own success: we’ve forgotten how bad infectious disease is.)

Vaccination does carry risks, if small ones – something that doctors like to minimize rather than underscore. But it’s also true that not vaccinating carries risks. (There’s a reason childhood mortality rates are significantly down.) The decision to vaccinate requires a weighing of personal risk against a weighing of benefits to the group – and especially to those most vulnerable within the group, including babies and the elderly. Like many people, I had moments of feeling nervous about vaccines and their effects on developing immune systems. Yet I couldn’t live with myself if one of my children’s bodies caused harm to the vulnerable among us.

Vaccination, like American politics, is polarized and polarizing. The irony is that it is through its pursuit of ultimate individualism – the exercising of the right not to follow recommendations – that it becomes a dangerous reminder that our bodies, like the body politic, are fatefully interconnected.