In her poem “Snapshots of a Daughter-in-Law,” Adrienne Rich writes of a woman who is “Poised, trembling and unsatisfied, before / an unlocked door, that cage of cages.” The subject of these lines is unclear, and so is the boundary between the woman and the cage; only the relation between the two is firm, defining. It is also alienating, divisive and halting. Like Rich, Eula Biss—essayist, poet, linguistic trespasser—has an eye for identifying insecurities around dividing lines. Her uncanny knack for seeing cages that entrap others is continuous with her talent for anxiously building them around herself.

In 2008, Biss won the Graywolf Press Nonfiction Prize and published her first collection, Notes From No Man’s Land. Over the course of thirteen essays and innumerable apologies, she travels from New York to California to the Midwest, pointing out along the way the borders that arrange black, brown and white bodies. The collection won a National Book Critics Circle Award, and Biss was hailed as the next Joan Didion, possibly because she wrote her own essay titled “Goodbye to All That.” But Biss is more off-putting than Didion ever was.

Of the woman in her poem, caught in the uncertainty trap, Rich asks, “Is this fertilisante douleur?” Is this fertile pain? Biss is drawn to the same question but frames it differently: Where language is simultaneously the force that locks up and liberates, can anything grow? In America, there is only one side to every border. You are a citizen or an alien, a productive member of society or an invisible one; you’re in or you’re other. Biss explores why this is not a logic problem, but instead a problem of language and of metaphor in particular.

In Notes, Biss writes often about how she, as a white woman, is a racialized subject. It is a privileged role that is, nonetheless, always putting words in her mouth. Biss fusses with her status of diffident white chick as if it were ten sizes too small on her. In the book’s title essay, she recounts some time she spent with her husband in Chicago, where she was teaching at a university. There she observed the history of redlining and played a part in the slow gentrification of her neighborhood, Rogers Park, one of the few racially diverse areas in the city. Her friends and family tell her repeatedly that Rogers Park is dangerous, and Biss comes to resent her racial prerogative to pay for safety with her own detachment from the community. Still, she admits to experiencing her whiteness as a wall between herself and her neighbors. “So many of us have agreed to live within a delusion,” she writes, “that we will be spared the danger that others suffer only if we move within certain very restricted spheres.” The tension between withdrawal and engagement manifests itself in many poignant but undeniably awkward interactions. One night, on the way home, Biss and her husband encounter a group of black boys drinking and riding their bikes on the street and having a good time. As they cross the street to their apartment, one of the boys shouts after them, “Don’t be afraid of us!” Biss doesn’t reply, hurrying toward the gate of her apartment building, unsure of how she should have reacted and full of shame.

In her new book, On Immunity, Biss crosses a threshold into a completely different subject—inoculation in America—but enters it through a familiar door. A private security concern gives rise to a meditation on public security, primarily public health. The book begins with—and always returns to—Biss’s concern for the health of her young son. Worry over how many shots her son is receiving leads her to the Internet, where she invariably stumbles across the anti-vaccination conspiracy theories of the American right, which decry adjuvant injections as hotbeds of diabetes, asthma, allergies and autism. Although Biss is skeptical of parents who accept these theories wholesale, she is sympathetic to their fears and even suffers her fair share of anxiety over her son’s collateral chemical intake. She remembers the time she called her husband in tears because she had read online that the plastic cover on her son’s mattress might release toxic gases, according to “preliminary research.”

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Biss’s central thesis is that “The natural body meets the body politic in the act of vaccination, where a single needle penetrates both.” This is an ambitious and wide-ranging area of exploration. The ways in which our bodies come into contact with and are circumscribed by the state are seemingly endless. Yet following the thread of this argument through the book is often like trying to find a hypodermic needle in a haystack. In one section, Biss writes about the sterilization of vaccines: how they are filled with preservatives, more mechanized than organic, resulting in unforeseen consequences for the health of the vaccinated. They are the products of big pharmaceutical companies, of capitalism, which prioritizes speed and the elimination of toxins for the sake of efficiency—but, as with genetically modified organisms and pesticides, the costs have yet to be added up. This leads to a discussion of Victorian vampires, who, Biss argues, are agents of capitalism and of inoculation. For good measure, she throws in germ theory and some words by Mark Twain on faith before the chapter ends soon after.

On Immunity is decidedly panicked and slipshod, unlike Notes From No Man’s Land. Still, the book is full of brilliant moments, and, as with its predecessor, some of its most effective and interesting discussions are those that charge into the fray of American racism, this time by using the subject of vaccination as a spear.

Beginning in 1898, a smallpox epidemic tore through the United States for a little more than five years, infecting thousands. Many at the time believed that whites could not be infected, so blame for the death and destruction fell squarely on immigrant and black populations. A swarm of racial slurs—“Nigger itch,” “Italian itch,” “Mexican bump” among them—spread along with the disease. Eventually, both the illness and its social stigma reached New York City, where police were dispatched to Irish and Italian immigrant neighborhoods in order to force inoculation upon them. In Middlesboro, Kentucky, black residents were inoculated at gunpoint.

At the time, Biss writes of these events, “the bodies of the poor were seen as a liability to public health, as dangerous to others.” In the nineteenth century, the metaphor for illness that most captivated the American imagination was “filth”—a rhetorical device as much as a poetic one, one that paired perfectly with the pathogenic belief that poor and minority Americans were inherently dirty or impure. In this single word, the lines between immigration, race, policing and medical science were clumped together in a single putrid ideology.

Throughout her book, Biss powerfully invokes “herd immunity,” the notion that if a critical portion of the population is inoculated, the entire community will be immune from disease. It is usually not known where this threshold lies until we pass through it. Black Americans may no longer be vaccinated under threat of death, but in a country where minority-majority status is still drawn along racial lines, herd immunity is a radical notion, because it implies that we are all responsible for one another’s bodies. “Herd immunity, an observable phenomenon, now seems implausible only if we think of our bodies as inherently disconnected from other bodies,” Biss writes. “Which, of course, we do.”

A 2004 analysis of CDC data affirmed as much: it showed that unvaccinated children were more likely to be white and to live in a household with an income of at least $75,000. “Public health, we assume, is for people with less—less education, less healthy habits, less access to quality health care, less time and money,” Biss notes. In fact, the question of exactly who benefits from public health becomes more complicated from the standpoint of security. Suspicions about shared health have more to do with how risk is assigned and fears apportioned than with a rigorous analysis of who is protecting whom.

Another study found that subjects who were told stories of the spread of harmful bacteria later had more conservative opinions when they were asked questions about immigration policy. This suggests that “infection” and “immigrant” are still metaphorically connected in the minds of the American public. Flashes of Biss’s earlier work can be seen in her insistence that public health is sliced into regions, much like urban areas are. In both cases, race and citizenship act more often than not as boundaries. And just as we cannot understand America without conceiving of “the other,” we cannot understand contagion without some conception of the quarantined subject.

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That the history of vaccination in the United States has been about the poor being obliged to protect the privileged, Biss argues, is one of many reasons why the topic is deeply enmeshed in the language of war. Americans call vaccines “shots,” the British “jabs.” And, she points out, “the term conscientious objector…originally referred to those who refused vaccination.” The term came into being in the late nineteenth century through efforts to resist Britain’s Compulsory Vaccination Act of 1853.

I found myself nodding along with most of this, but perturbed by how much the metaphor doesn’t explain (metaphors, like people, are, of course, so flawed!). Why, for example, are those Americans who are most mistrustful of vaccines so often the same people who champion their right to carry guns? Biss has a tendency to meander into positions that are too sweeping and difficult to defend.

More intriguing and complete are the connections that she makes between vaccination and global outbreaks of disease as a way for national governments to forestall suffering through never-ending wars. From SARS to the H1N1 flu to the Ebola virus, the United States orders pre-emptive strikes against global health crises, isolating and inoculating ourselves against them before they can creep across our borders. And yet, much like the terrorist threats that go into remission only to emerge in new states, the fear of a pandemic coming to our shores is always looming. Infections are a perfect enemy because they are an inevitable enemy, Biss argues. By the time a cure is found and we are inoculated against the disease, the disease is already inoculated against us through ideology. This too feels like a continuation of Biss’s earlier work: in her essay on Chicago, Biss writes that “one of the paradoxes of our time is that the War on Terror has served mainly to reinforce a collective belief that maintaining the right amount of fear and suspicion will earn one safety.” This fear of what lies beyond the border unsettles us, but it also gives us balance, coherence, poise.

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Biss’s approach to immunity is reminiscent of Susan Sontag’s Illness as Metaphor (1978). Sontag established that military metaphors were first used to describe medical conditions in the 1880s, when bacteria were recognized as a cause of illness. This history squares nicely with Biss’s reading of infections as meandering, stateless agents of chaos and war. Similarly, Sontag argues that metaphors, war among them, march in lockstep with disease and medicine as repressive measures. “Nothing is more punitive than to give a disease a meaning,” Sontag writes, “that meaning being invariably a moralistic one.” Whether tuberculosis is romanticized or cancer militarized, metaphor narrows the possibilities for understanding bodies in peril.

Sontag’s essay is famous for its disavowal of metaphorical language. The purpose of Illness as Metaphor, writes Sontag in AIDS and Its Metaphors, published a decade later, “was to calm the imagination, not to incite it.” Her approach, as she describes it, is both “polemical” and “practical.” Metaphors obscure power, therefore we should remove the blockage.

On this point Biss diverges from Sontag radically, in an astonishing new way. Over the course of her new book, particularly around her discussion of herd immunity, a powerful argument in support of metaphors takes shape. “Fear of contamination rests on the belief, widespread in our culture as in others, that something can impart its essence to us on contact,” Biss writes. So we throw up the walls and disseminate the policies that keep us sheltering in place. What Biss proposes is a kind of metaphorical thinking that embraces the reality that we are “continuous with everything here on earth. Including, and especially, each other.”

Biss ends On Immunity by likening society to a garden, “unbounded and unkempt, bearing both fruit and thorns.” In this reconfiguration, the health of our individual bodies is not equivalent to the health of the nation, but is dependent upon the health of one another. The process of growing through and into one another is painful, but it is also lush: “Perhaps we should call it a wilderness. Or perhaps community is sufficient.”

The garden is reminiscent of a no-man’s land—a place that does not recognize sides, where there can be a brief reprieve from violence. It seems far too idealistic far too often, yet is tethered to territories, which lend it definition. Creating an opening into it requires wild imagination and courage, finding doors in the walls. Like the gate to Biss’s house in Rogers Park, which “gives the appearance of being locked but is in fact always open.”