It’s a puzzle of public health that we don’t take flu seriously. Every year, only about half of American adults get the vaccine that prevents it. And yet, every year, at least 37 million Americans catch the flu, more than 500,000 become sick enough to be hospitalized, and somewhere between 36,000 and 61,000 die. Let’s pause for a second: That’s tens of thousands of deaths, many of which could have been prevented with a simple shot. Meanwhile, international health planners tensely monitor the unpredictable evolution of the flu virus, watching for the emergence of a pandemic strain that could kill many millions.

Yet perhaps because only a small percentage of cases ends catastrophically—or conversely, because many of us have experienced recovering from flu—we chronically underestimate the toll taken by the virus. Which might be the kindest explanation for the decision by US Customs and Border Protection, uncovered last week by CNBC, not to give the flu shot to any of the adults or children the agency is holding in crammed border camps.

Equally likely explanations: racism, prejudice, and outrageous disregard, along with a misguided belief that withholding health care—like the already-documented denials of showers, blankets, hot food, and enough room to lie down—will deter more migrants from coming.

Whatever the reason, the decision to withhold flu shots denies human rights, defies international treaties and legal conventions, and is epidemiologically dangerous and dumb.

Maryn McKenna (@marynmck) is an Ideas contributor for WIRED, a senior fellow at the Schuster Institute for Investigative Journalism at Brandeis University, and the author of Big Chicken.

Not to mention very badly timed. One day after the border agency’s ruling became public, the US recorded the first death of the 2019-20 flu season, a 74-year-old man living near San Diego. That means the flu season is getting an unusually early and deadly start. The agency told CNBC, and later other news outlets, that it was making the flu shot decision because of “the short-term nature” of its camps, which operate under a 1997 agreement limiting child detentions to 20 days. But the administration simultaneously announced it intends to abandon that agreement and plans to detain families with children indefinitely—which would leave many more people vulnerable to the flu.

The danger is easy to grasp. Flu is a respiratory disease, passed from person to person by droplets of lung secretions that travel a few feet when an infected person sneezes or coughs. The closer people are to each other, the more likely it is that an uninfected person will inhale those droplets, conducting the virus into their airways. The more depressed that person’s immune system, the more likely it is the virus will find a home in their airways and trigger an infection and disease.

The crowding in the detention centers is self-evident, and the physical and emotional conditions that migrants endure there and on their journeys—hunger, dehydration, filth, stress, sleep deprivation, and anguish—are known immunological dampers. The camps are an almost perfect arena for transmitting a respiratory disease.

The camps are an almost perfect arena for transmitting a respiratory disease.

Failing to protect detainees from a disease their detainment exposes them to may also be illegal under international law. Legal scholars mainly disagree on how to talk about that law-breaking, when detaining children at all may also be illegitimate under commitments such as the International Convention on the Rights of the Child. (The United Nations High Commissioner for Human Rights, Michelle Bachelet, said last month that she is “appalled” by the detention conditions, adding: “Border management measures must comply with (a) State’s human rights obligations.”)

“The decision to not give people in these detention facilities influenza vaccine is misguided, shortsighted, and unethical, and may be a violation of their human rights,” agrees Alexandra Phelan, an infectious disease expert and a faculty research instructor at Georgetown University’s Center for Global Health Science and Security. “It’s incredibly dangerous.”

That’s not a hypothetical. Since December, three children confined at the border have died of the flu, according to a letter sent to Congress by physicians before the flu-vaccine policy was disclosed. The doctors wrote that there may be 200,000 children in detention, and that last season, there was only one flu death per 600,000 children in the rest of the US—rendering children’s risk of dying from flu approximately nine times higher inside the camps.