Deb Horning, a survivor of a rare form of acute leukemia, never leaves her house without hand sanitizer, wipes and a face mask.

She recently stopped into her son's high school to ask what percentage of students had been vaccinated against measles. Next month, the Billings, Montana, mother of four is supposed to fly to her hometown of Chicago — a trip she is considering canceling for fear that it might expose her to measles, a disease once declared eliminated in the United States that is now popping up in outbreaks across the country.

Horning was diagnosed with the blood cancer in October 2014, and was told the type she had has a 25 percent chance of survival. Following intensive chemotherapy and a stem cell transplant, her leukemia is now in remission. But the treatment wiped out her immune system, leaving her "like a newborn," she said.

Deb Horning, left, seen with her husband James Horning and their four children, is in remission from a form of leukemia that doctors gave her a 25 percent chance of surviving. Courtesy Deb Horning

As a result, Horning, 47, has no natural protection against contagious illnesses, and is susceptible to getting a more severe case of whatever she catches. Measles, a systemic infection, could kill her.

"All the things that I had to deal with — I’ve survived all this stuff — just to get whacked by the measles? I didn’t go through all this for that."

"I think hand washing is huge, but it’s not going to save me from the measles, and yes, I am freaked out by this," Horning said. "All the things that I had to deal with — I’ve survived all this stuff — just to get whacked by the measles? I didn’t go through all this for that."

There have been more than 760 cases of measles in America this year — the highest number in 25 years. The disease, a common childhood illness decades ago that is now preventable with vaccines, was declared eliminated in the U.S. in 2000, but has made a resurgence in 2019, with cases in 23 states so far.

With measles scares happening everywhere from movie theaters to cruise ships to planes, individuals with compromised immune systems and their families are upending their daily routines to avoid getting the highly contagious disease. They are staying away from public spaces, placing panicked calls to their doctors, and taking to social media to implore others who can get vaccinated to do so.

And unlike vaccine-hesitant parents who choose not to give their children the measles, mumps and rubella, or MMR, vaccine based on arguments discounted by science or those who object for religious reasons, many with weakened immunity desperately want to get the shot to protect themselves — but cannot.

Horning got all her vaccinations long before she got cancer. But her leukemia treatment removed them from her immune system's memory.

Deb Horning, left, prepares to get a stem cell transplant from her sister, Susan Piroth, in February 2015, at the Mayo Clinic hospital in Phoenix as part of Horning's leukemia treatment. As a result of chemotherapy and the transplant, Horning has weakened immunity but cannot get vaccinated against the measles until she finishes a course of immunosuppressant drugs. Courtesy Deb Horning

She is eligible to get revaccinated against some illnesses, like the flu. But because she developed a condition called graft-versus-host disease after she received a stem cell transplant from her sister in February 2015, where the transplanted stem cells attack her body, she has to take immunosuppressant drugs.

Those drugs mean she cannot get live vaccinations like the MMR, because unlike a healthy person whose immune system will respond to a small dose of a disease by creating antibodies against it, her immune system would not. Her doctors say she must wait two years after she is off the immunosuppressants before she can get such vaccines, and they are not ready to take her off the drugs yet.

There have not been measles outbreaks reported yet in Montana, where Horning lives, but she said she has been checking the Centers for Disease Control and Prevention website frequently to monitor where the cases are.

An upcoming trip to Chicago that she has been planning for five years, since before she got leukemia, has her nervous. She is supposed to meet up with a longtime friend there who does not vaccinate her children, and Horning is considering canceling the get-together, or even the entire trip.

Horning is not alone. At the Memorial Sloan Kettering Cancer Center in New York — the state that has seen the most measles cases so far this year — Dr. Miguel Perales, a medical oncologist and deputy chief of the bone marrow transplant service, said almost every patient of his asks how to protect themselves from measles.

"They're worried about being around kids, going to the movies, the store, anywhere where there's kids," he said. "Patients are very worried about their risk of exposure, and not just immediate exposure, but indirect exposures through other family members, other children."

Perales advises patients to carry a mask and a pair of gloves in their pocket, and to put them on if they are out in public with large groups of people.

"These are patients who have potentially fatal diseases and we have given them a treatment that can cure them, and there are risks involved. But to have this added risk, which in my mind was avoidable, just makes it worse."

"There's a limit to what we can say," he said. "It is very frustrating, obviously. These are patients who have potentially fatal diseases and we have given them a treatment that can cure them, and there are risks involved. But to have this added risk, which in my mind was avoidable, just makes it worse."

Dr. Bill Moss, an epidemiologist, pediatrician and interim executive director of the International Vaccine Access Center at the Johns Hopkins Bloomberg School of Public Health, said most of the research that has been done on the effect of measles on people with compromised immunity was on those with HIV.

"People who are immunocompromised are more likely to get severe measles, more likely to die from measles and more likely to have unusual presentations of it," he said, adding that they may not develop the recognizable rash typically associated with measles, leading to the virus going undiagnosed for longer.

The virus is spread through respiratory droplets when infected individuals talk, sneeze or cough. It can also stay suspended in the air for a couple of hours once an infected person leaves the area, Moss said.

"Obviously, the best way of protection is vaccination, but if that's not possible, then you would just be very careful when there are measles outbreaks in an area. Try to avoid those kinds of places," he said.

That is what Horning, the Montana mother, plans to do.

"Everywhere I go now, I think about it," she said. "When I go shopping, it used to be way back in my mind, like, 'I could get sick easily.' But now it's way in the front of my mind."