Catherine Montantes was a 28-year-old college student, training to become a border patrol agent, and recently diagnosed with an autoimmune disorder.

When she stepped into the Lower Elwha tribal health clinic in Port Angeles, Washington, she had no idea she arrived just an hour after a 52-year-old infected with measles. The virus is one of the most contagious and can live on infected surfaces for up to two hours.

Despite being vaccinated against measles, Montantes was killed less than three months later by the disease, because her immune system was suppressed by medication to control the autoimmune disorder dermatomyositis.

Her death, on 8 April 2015, became the last recorded death from measles in the United States. At the time, no one had perished from measles in 12 years. Now, as a record-setting measles outbreak spreads in 28 states, with the majority of cases in New York, her death shows how preventable diseases can devastate families far outside the communities which choose to delay or decline vaccines.

In an exclusive interview with the Guardian, Montantes’s mother, Ralphenia Knudson, describes how the disease, often called “harmless” by anti-vaxxers, claimed her daughter’s life and upended her family.

“You don’t have a right to play with other people’s lives like that, you don’t get to choose – ‘OK we’ll let it run its course, we’ll make them tough’,” Knudson said. “You’re not going to make them tough, you’re exposing them to a deadly virus their body won’t be able to fight and that’s what happened.”

Montantes was the first person to die of measles in the US since 2003. Since Montantes’s death, at least 1,655 people have been sickened with measles in a series of outbreaks across New York, California and Washington. Statistically, the US Centers for Disease Control and Prevention is likely to find one person killed by the disease in 2019, a record year for measles with 1,077 cases.

“I understand the importance of vaccination. I had all my kids vaccinated,” said Montantes’s mother, Knudson, a former long-haul, semi-truck driver who lives in Juneau, Alaska. Montantes had three siblings. Her sister, who was contacted by the Guardian, declined to comment for this story, saying her sister’s death was still too difficult for her to talk about.

Vaccine hesitancy was named a top 10 global health threat by the World Health Organization this year. By this April, measles cases had risen 300%. In its decision to call vaccine hesitancy a global health threat, the WHO attributed the virus’s rise, in part, to people declining or delaying vaccines despite their availability.

Although reasons to decline vaccines are often multi-faceted, in the United States the rise of misinformation spread through social media by anti-vaxxers has played a prominent role in one of the worst measles outbreaks in nearly a decade.

Most of the cases are concentrated in conservative Orthodox Jewish communities in and around New York City. Prominent anti-vaxxers, who have targeted a close-knit Somali community in Minnesota, have visited the city to spread propaganda and false claims about the dangers of vaccines.

Unvaccinated children and those with suppressed immune systems – like Montantes – are the most vulnerable to measles, which kills between one and two people for every 1,000 it infects. The virus can also cause brain inflammation, called encephalitis, and permanent brain damage at about the same rate. In 2017, measles killed 110,000 people, mostly children under five, according to the World Health Organization.

By contrast, it is possible – though not proven – that the measles component of the MMR vaccine could lead to encephalitis in less than one patient per 1m doses. Put another way, the vaccine is at least 1,000 times less risky than not vaccinating, according to the World Health Organization.

“[Measles exposure] is dangerous, especially for those who don’t have an immune system when it is suppressed by medication,” said Knudson. “The law states you’re supposed to have your kids immunized, that’s what the law says. If you can’t follow it, there should be consequences for that.”

Montantes was diagnosed with dermatomyositis just months before she was killed by measles. In November 2014, Montantes, a Mexican-Alaska Native, was studying criminal justice at Peninsula College in Port Angeles, hoping to switch careers from dental hygienist to become a border patrol agent. That month, she was riding with her mother on her route as a long-haul semi-truck driver.

“One thing Cathy and I were able to do,” on trips, Knudson said, “was work out a lot of things between her childhood and what I messed up on … We ended up with a very close relationship.”

The two were at the Fedex hub in St Paul, Minnesota, when Montantes started to feel unwell, initially thinking she had a urinary tract infection. After she arrived at St John’s hospital, she started having difficulty breathing.

“They couldn’t figure out why Cathy was so sick,” said Knudson. Then, doctors took a tissue sample of her left arm. “That’s how they discovered [the disorder],” said Knudson.

In January, while on the immune-suppressant drugs often used to treat dermatomyositis, Montantes went to the Lower Elwha clinic in Port Angeles and was exposed to measles.

New York City’s Mayor Bill de Blasio declared a public health emergency in parts of Brooklyn in response to a measles outbreak. Photograph: Shannon Stapleton/Reuters

Montantes was ill for months before she passed away in a hospital in Port Angeles, still trying to get out of bed in her final hours as she coughed up blood.

“Probably 36 hours before she passed away, I have video of her, and she was still trying to stand up,” said Knudson, bereft and hardly able to get out the words. “Even at that point, when we got to University of Washington [hospital] and put her in the [critical care] unit, they didn’t tell me she was passing away.

“It wasn’t until they said I needed to notify my other kids to come by here if they wanted to see her,” said Knudson.

Knudson described Catherine as the tough, quick-witted “glue” of the family, always calling her three siblings to make sure they stayed in touch with her parents.

“That was one thing I always teased her about. She had a great sense of humor – this girl was quick,” said Knudson. “I just loved her to pieces.”

Montantes’s death sent her mother into a near “emotional breakdown”. Unable to continue driving her routes from Bismarck through Texas, Utah and Indiana, Knudson moved to Juneau to care for her mother. Montantes’s siblings continue to struggle with the loss.

Montantes’s identity was first revealed in the Seattle Times a year after her death. The Guardian confirmed her identity through state death records. Health authorities never released the name of the 52-year-old man who started the outbreak. And although Montantes was the only person to die as a result, the outbreak did not stop at the Lower Elwha clinic.

The man may have exposed as many as 149 people, the Seattle Times reported at the time, including a five-year-old girl whose infection led to the closure of a private Christian school.

A sign in Brooklyn, New York, advises about the measles outbreak. Photograph: Carlo Allegri/Reuters

The girl took the virus back to her school, the Olympic Christian Academy attended by 115 students – including an estimated 18 who were not vaccinated – according to state records and Seattle Times reports from the outbreak.

Olympic Christian still has a “chunk of parents who don’t believe in immunizations”, said Tiffany Gillespie, the principal, and a teacher during the outbreak. Gillespie said parents believe common lies spread by anti-vaxxers, including the falsehood that vaccines “can be linked to learning disabilities, and there is not enough research out on it yet to say they are not linked to autism or other disabilities”.

“Some say they contribute to Alzheimer’s when they are older,” Gillespie said, and added, “I haven’t personally taken the time to research, I just went for vaccinations.” Vaccines are one of the safest and most widely tested medical interventions in human history.

Montantes’s case not only shows the toll such deaths can take on families, but how difficult it is to capture the toll of a disease such as measles. Her infection was only diagnosed after death, during an autopsy. US states are responsible for measles investigations, and then must report them to the federal authorities.

“Cathy just loved life,” said Knudson. “She loved life, and she wanted to live.”