The one-day immunisation clinic at David Douglas High School in Portland, Oregon, was hectic on Saturday, with a wait of 45 minutes to more than an hour just to see a nurse.

But Cameron Wagner said that after balking this long at getting her 4-year-old son vaccinated, out of concerns about potential side effects, a few more minutes would not matter.

“I’ve talked to more doctors and have weighed the options, and decided to come in and get a shot,” said Ms Wagner, 46, a massage therapist.

Measles, which has broken out in the Pacific Northwest and elsewhere this year, was a major force in her changed thinking.

She said she had been keeping Lux, her son, out of play spaces and other crowded public areas in recent weeks as alarming reports flooded the news, and she was tired of it.

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As the outbreak has flared, vaccination rates have soared in a state where the percentage of residents who decline vaccines for nonmedical reasons — 7.5 per cent, according to the US Centres for Disease Control and Prevention — is the highest in the country.

Parents of unvaccinated or undervaccinated children like Lux have come forward, raising health officials’ hopes that perhaps a corner has been turned.

In Oregon and southwest Washington, where measles cases have clustered, about triple the number of children have been vaccinated this year, compared with the same period in 2018.

Since 1 January, 10 states, according to federal health records, have reported cases of measles, which was declared eliminated as a major public health threat nearly 20 years ago.

Of the 101 cases confirmed across the nation, 53 were in southwest Washington, just across the Columbia River from Portland, and four were in Multnomah County, which includes Portland.

Refusal or resistance to vaccination — which health experts say can raise the chances of an outbreak by putting at risk people who cannot be immunised for medical reasons — might be connected to a broader anti-vaccination movement, including concerns that vaccines lead to autism, an idea that has been widely debunked.

But fears incited by the outbreak could trump those concerns, experts say.

“I’m an optimist,” said Dr Jennifer Vines, deputy health officer for the Multnomah County Health Department. “But it’s hard to predict long-term,” she added.

Around Oregon and within Portland, the percentage of children unvaccinated for measles varies widely from school to school, with most at or near the threshold protection levels that epidemiologists say keep the virus at bay, about 93 per cent.

Still, at some Portland schools, 10 to 20 per cent or more of their students are unvaccinated for nonmedical reasons.

At least seven schools have measles vaccination rates lower than 80 per cent, which is lower than some developing countries like Guatemala, where 86 per cent of children between 12 months and 23 months old are protected against measles, or India, with 88 per cent, according to a World Bank study.

The clinic on Saturday shed light on some of the myths, and nuances, about people who do not get their children vaccinated, medical experts said.

On that spectrum of people are hard-core refusers, who decline all vaccines and believe them harmful; moderates who worry about the timing or clustering of vaccines and their side effects; and parents who are simply overwhelmed with so many other aspects of their lives, from economics to health insurance, that vaccination slipped off the table.

Vaccine advocates say gentle persuasion, and the occasional deadline, work better at convincing families to protect their children than attacks.

“We do a disservice if we sort of denigrate or shout at families who choose not to vaccinate, because it’s understandable: They don’t want to do any harm to their kid and they’ve heard so much that’s negative,” said Dr Matthew F Daley, a paediatrician and researcher who works on public vaccination issues. “We need to meet them where they’re at.”

But health officials have not won over everyone just yet. Ms Wagner, who was at the clinic with her son, said she had not changed her mind on the safety of all vaccines.

The MMR combination shot — for measles, mumps and rubella — was all Lux would be getting, at least for now.