Shocking news today out of Washington state: For the first time since 2003, a resident of the United States has died of measles. If you wondered, based on my last post, what happens when measles infects unvaccinated people and travels with them in an untrackable manner, this is the answer: It sickens and kills people who are vulnerable for reasons over which they have no control.

As the Washington State Department of Health reported today, the victim is a young woman from Clallam County, which is the northwesternmost point of the state. (The county is pretty thinly populated—most of its area lies within Olympic National Park—so to preserve her privacy, the state department is not giving out too much information.) Because of other health problems, which the department hasn’t specified, the woman was taking drugs that suppressed her immune system. Drugs such as those also suppress immune protection to measles from vaccination or from having had the disease.

The woman was getting medical care at a local facility in Clallam County (update: according to further state information, a local community health clinic), and crossed paths there with another patient who later developed the telltale measles rash—but, because this is how measles unfolds, was capable of infecting others before the rash developed. As the Centers for Disease Control and Prevention noted last week, while investigating a case in which someone was infected just by walking through a gate at an airport, measles is extremely contagious. Any one case of measles can infect on average 18 other unvaccinated/unprotected people; the equivalent number for HIV is 4, and for Ebola is 2. (The American Academy of Pediatrics, not known for being alarmist, calls measles “one of the most highly communicable of all infectious diseases.”)

According to investigative work by the state department, the woman had been vaccinated, though spokesperson Donn Moyer told me her mother was not able to locate a vaccination record. (Update: According to further state info, the woman learned she might have been exposed to measles; had her degree of immune protection checked, and discovered she would have had enough immunity to protect against measles if she had not been taking the immune-suppressing drugs.) Nevertheless, because of the immune suppression, she became infected. And, also because of the immune suppression—this is important—once the disease developed, she did not experience the characteristic rash. Instead, she developed pneumonia. That was one of the chief causes of death from measles in the pre-vaccine era. But measles pneumonia is now so rare—because measles itself is rare, though not as rare as it was—that it is not the first explanation that leaps to mind when a case of pneumonia occurs.

The actual cause of the woman’s illness was only revealed after she had been hospitalized at a second medical facility, and died, and underwent an autopsy. According to the state health department: “The cause of death was pneumonia due to measles.”

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Infographic courtesy CDC.gov; original here

I asked Dr. Anne Schuchat, the director of the CDC’s National Center for Immunization and Respiratory Diseases, her thoughts about the Washington case.

“Measles can be serious, even deadly, and in this case it was,” she said by phone. “As we have been telling people, we need to achieve very high rates of measles vaccination to protect the most vulnerable: babies and people who are immunosuppressed. While measles can be deadly in anybody, it is more likely to cause this kind of complication in people with immune-suppressing conditions.”

It’s no secret that the protection afforded by measles vaccination is crumbling in the US, thanks to parents who have been given bad information turning away from the vaccine. Last year—a year in which the US experienced a record number of measles cases—CDC research found this: “Despite a national MMR vaccination coverage level of 91.9%, one child in 12 in the United States is not receiving their first dose of MMR vaccine on time, underscoring considerable measles susceptibility across the country.”

When people prevent or delay their children’s vaccinations, it isn’t only their children they put in danger. The fence of protection that vaccine-induced immunity throws up around all of us protects not only those who are vaccinated, but those who can’t be: infants too young to get the vaccine and anyone who, like the Washington woman, possesses an immune system undermined by medical treatment or biological hazard. (And, most of the time, older people whose immune systems are decaying—but not in the case of measles, because anyone born before 1957, when measles was common, has natural immunity to the disease.)

Those unknown vulnerables represent a lot of people: cancer patients undergoing treatment, transplant recipients taking anti-rejection drugs, people living with HIV, anyone with an inborn immune deficiency, anyone getting high doses of steroids—and the 4 million children in the United States who at any point are less than 12 months old, the recommended age for the first dose of measles vaccine. As New York physician Kelly A. Chiles said on Twitter, hearing about this case:

Immune suppressed pt dies of measles. Tragic. THIS is what parents of kids with cancer fear #vaccinateyourdamnkids https://t.co/wtktx5X0Si

— Kelly A. Chiles, MD (@kachiles) July 2, 2015

If any vulnerable child were infected in a clinic or a waiting room by another, unvaccinated child, that death would be horrific, because it would have been preventable. Perhaps the legacy of this woman’s sad death will be to make that horrific possibility less likely.

Going forward, a great resource for understanding parents’ vaccine hesitation is journalist Tara Haelle. For further news about this case, a good person to follow will be JoNel Aleccia, the excellent health reporter at the Seattle Times. And for the sad story of why parents turned away from  vaccines, you cannot do better than Seth Mnookin‘s book The Panic Virus.