HELENA -- Federal health officials are worried about a measles outbreak spreading to the United States, especially to places like Montana that have a lower vaccination rate for measles, mumps and rubella.

British authorities announced last month that the United Kingdom faces an impending measles outbreak this winter because many parents refuse to vaccinate their children citing scientifically unfounded concerns that vaccines are linked to the neurological disorder autism.

Earlier this month, U.S. health officials cautioned that an outbreak across the Atlantic could lead to an outbreak here, especially in places with low vaccination rates.

Montana is among a handful of states and counties across the country with a vaccination rate below 87 percent -- a rate experts believe could allow an epidemic to take hold.

Only 67 percent of Montana 2-year-olds are vaccinated against the standard suite of childhood diseases, including measles, polio, whooping cough and others, said Joyce Burgett, program manager for the Montana Immunization Program. The rate for measles, mumps and rubella is just over 85 percent.

That rate is so low that a person carrying measles could spread it to enough unprotected children to establish an epidemic, she said.

''We always worry about measles," said Jim Murphy, the state's communicable disease surveillance officer.

Measles can spread ''from any place to any place," Murphy said, but the United Kingdom is a particularly popular spot for measles to spread because it's more common for Americans to visit the United Kingdom and vice versa.

To that effect, the state has a broad measles surveillance program, with doctors reporting any possible measles cases to the state. So far, said Murphy, there hasn't been a reported case of someone catching measles in Montana in more than 10 years.

Just why parents sometimes don't vaccinate their children is difficult to pin down.

''Some people have philosophical objections to vaccinations," Murphy said. ''They don't think it works."

Other parents fear that vaccinations lead to autism -- a neurological disorder currently on the rise in the United States marked by difficulties relating to other people.

In fact, Murphy said, numerous studies have shown no relation between childhood vaccinations and autism.

Burgett said she thinks the rarity of measles and other common childhood killers now nearly eradicated by vaccinations reduces the drive for parents to immunize their children. Many parents have never seen a person with measles. The disease doesn't seem real, so the desire to vaccinate is less.

''All they see is the rare adverse effects," she said.

There is some good news. Vaccinations are required before children can enter school. Consequently, the vaccination rate for school-aged children in Montana is 99.8 percent.

The measles threat, then, is most concentrated in very young children.

''If someone carrying (measles) went to a school setting, it probably wouldn't sustain an epidemic," Burgett said. ''But if they went into a daycare setting where children are less than a year old, measles could spread through that group."