One in five toddlers across El Paso County went without the measles vaccine in the first half of 2014. Statewide immunization rates haven't been much better.
That, public health officials say, is a problem.
After tracking down hundreds of El Paso County residents recently exposed to the highly contagious virus, county health officials say the latest outbreak highlights an ever-present need for vaccinations that some parents question - putting at risk others who can't be immunized.
Few states have more lenient vaccination laws than Colorado, which only requires parents to sign a piece of paper stating they have a religious, medical or personal objection to the immunization. Doctors or public health officials are not required to approve the request.
Small changes could be coming this year, possibly requiring those forms to be turned in more frequently, rather than just once. Some fear the system does too little to protect those most vulnerable; others say it works as is.
The issue comes amid wavering support for vaccinations by some parents, who have sought to opt out of school immunization rules over fears the vaccines could cause other health problems.
It also comes as a national spike in cases has left state and county health departments scrambling to keep the virus from making a permanent return.
"Measles is the most contagious of the vaccine-preventable diseases," said Dr. Greg Wallace, with the Atlanta-based Centers for Disease Control and Prevention. "So if you're exposed to measles and you haven't been vaccinated, it's a very high likelihood that you'll get the disease."
Making a comeback
Once a common virus in the U.S., measles can mingle in the air and infect people at a remarkable rate.
For example, if a sick person sneezes, the air inside that room can remain infectious for at least two hours.
Most people fully recover, but in rare cases it can cause death. Other side effects can include pneumonia, encephalitis (a swelling of the brain) and miscarriage.
Until about 50 years ago, almost everyone contracted measles by the age of 15 - in part, because it was so difficult to avoid. Of the 3 million to 4 million cases each year, 400 to 500 people died, according to the CDC.
A decades-long vaccination campaign led the CDC to declare it eliminated from the United States in 2000.
Cases still arise in the U.S., but they only happen when people from elsewhere in the world - mainly the Eastern Hemisphere - travel to the U.S. and infect people who aren't immune. Americans who travel abroad also have brought it back.
Most years, fewer than 100 people have been sickened. But measles outbreaks have grown larger in recent years, said Wallace, who heads the CDC's domestic measles, mumps, rubella and polio program.
Last year, 644 people caught the virus, roughly triple the amount of any year since 2000.
An epidemic in the Philippines fueled much of the United States' record increase, and more than half of cases in America affected an Amish community in Ohio, Wallace said. Most patients had not been vaccinated or did not know if they had been vaccinated.
"Within any specific group, all you need is to have that importation into that community and it will find the people who aren't vaccinated," Wallace said.
The wrong vaccine?
The trend shows no signs of slowing in 2015.
As of Friday, an outbreak that began at two California theme parks had infected 41 people in the U.S. and one in Mexico, according to The Associated Press.
A woman sickened in that outbreak was treated at Penrose Hospital on Jan. 3 and exposed more than 300 people in El Paso County to the virus.
No one else had caught it as of Friday, and fewer than five people remained quarantined over the weekend - largely because they could not prove they were immune, said Dr. Bill Letson, El Paso County Public Health's medical director.
The last day symptoms could appear is Jan. 24 because the virus incubates for up to three weeks.
The department is working to confirm whether the infected woman received a version of the vaccine used in the mid-1960s that wasn't as effective, Letson said.
The vaccine used since 1968 is 95 percent effective with one dose, and even more effective with the recommended two doses, he said.
"In that patient's case, we're not sure," Letson said last week. "We think that she got a vaccine, but we don't know which one."
Too many unvaccinated
To keep the virus from once again taking root in the U.S., experts say 90 percent - perhaps even 95 percent - of people need to be vaccinated.
In Colorado, that vaccination rate needs to improve, said Lisa Miller, state epidemiologist with the Colorado Department of Public Health and Environment.
In 2013, 86 percent of children ages 19 to 35 months old had at least one dose of the measles, mumps and rubella vaccine, according to the National Immunization Survey.
Over the first six months of 2014, 80 percent of children in that age range in El Paso County had that shot.
"We should be doing better," Miller said.
Public health costs can grow once it does appear. Health departments try to contact anyone possibly exposed to the virus once someone becomes infected as a means of checking its spread.
In El Paso County, at least 10 people in the health department dedicated most of the last two weeks tracking down people who visited Penrose Hospital, Letson said. Other agencies - including the Tri-County and Boulder health departments - were asked to help.
The exposures were limited by the fact that the Penrose Hospital's air circulation system did not mix contaminated air beyond the emergency room, CAT scan facility and the fourth floor, he said.
The biggest concern is people whose immune systems are compromised, or who can't get the vaccine even if they wanted it, including cancer patients and children under the age of 1.
The last major outbreak - which sickened 55,000 people and killed more than 100 people from 1989 through 1991 - disproportionately affected low-income children. One reason: Their families had a harder time accessing health care and the vaccine.
A massive federal vaccination effort, the implementation of a two-dose regiment and health care reforms in recent years have sought to address that need.
Still, a University of Colorado at Denver researcher said that issue remains a concern. Children whose parents opt not to give them vaccines often come from higher-income families, whose mothers have more time and resources to make such decisions.
"All parents have to consider whose children they're responsible for," said Jennifer Reich, an associate professor of sociology at CU Denver. "The parents I study feel they take vaccine choice very seriously. They spend a lot of time and energy thinking about vaccines.
"But they only feel responsible for their own children."
Worth the risk?
A bill last year sought to toughen regulations on avoiding vaccines.
Last year, Dan Pabon, D-Denver, introduced legislation that would have required parents seeking an exemption to take an online education course about the risks and benefits of being immunized.
It passed, but only after the requirement was stripped and replaced with a call for the Colorado Board of Health to examine how often parents must submit paperwork exempting their children.
School districts must also release immunization and exemption rates upon request and the state must create an online education module, though viewing it isn't mandatory.
Among those concerned about it was Theresa Wrangham, executive director of National Vaccine Information Center.
Living in Louisville, southeast of Boulder, Wrangham said she initially began having her children immunized, but gradually stopped after doing research. She also said she suffered seizures after getting a vaccine as a child in the 1960s.
People typically contact the organization about the influenza and human papillomavirus vaccines, she said, and their concerns often center around risk of shots' side effects. In some cases, parents have decided that the effects of a virus - such as measles - are not as bad as those risks, she said.
"I think parents have a right to evaluate that risk and decide what risk they're willing to take with their children," Wrangham said.
Reich's research found that people refusing vaccines occasionally cite a discredited British study from the 1990s that claimed vaccines cause autism - despite the fact that it has since been retracted, and subsequent studies have debunked the claim.
More often, the parents said they didn't trust vaccine ingredients made by pharmaceutical companies, Reich said.
Count Alisha Morales, a Colorado Springs mother of four, among parents who steadfastly seek vaccines.
She vaccinated three of her children - ages 9, 7 and 1 - after doing her own research, and has yet to have problems. Her youngest child is 2 months old, meaning he's too young to get a measles shot.
For other children to go without it would be "irresponsible," she said.
"They're taking more than just their child's life into their hands," Morales said.