While the vast majority of parents in the United States have their children inoculated against measles, a small but growing number are saying no to vaccines.

Those who refuse the immunization cite concerns about the vaccines causing illness, allergic reactions or neurological problems.

Government agencies and most doctors, however, say the risk is minimal, and is overshadowed by the risks of contracting the disease.

In Bucks County, the Woodlands Healing Research Center in Quakertown carries a lengthy vaccine informational piece, offering benefits and caveats, on its website.

The piece states scientific evidence shows while vaccines prevent infectious disease, it does not support their safety.

Parental choice is the deciding factor, the website states.

Calls to the center were not returned.

Locally, Dr. Peter Baddick says the resurgence of the disease is a "historic development as our state has not seen this disease in generations. It is perhaps the most infectious viral disease on the planet."

Most people who contract measles recover without any lasting damage. But children under 5 and adults are more likely to have complications, according to the U.S. Centers for Disease Control and Prevention.

Those complications can include hearing loss, developmental delays and pneumonia, the most common cause of death from measles in young children.

Children are typically immunized against measles at 1 year, and again at 4 or 5. Two doses is all a person needs for immunity, says Dr. Tibisay Villalobos, of the Pennsylvania Chapter of the American Academy of Pediatrics and a practicing pediatric infectious disease specialist in the Lehigh Valley.

But babies under 1 year and some people with suppressed immune systems cannot get vaccinated, and they are most at risk if they catch the disease.

Vaccine history

Many are blaming the growing number of unvaccinated people for the current rise in measles cases in the United States.

An outbreak at Disneyland in Anaheim, Calif., in December [2014] that spread to 102 people in 14 states alerted health officials to the problem.

The U.S. Centers for Disease Control and Prevention logged 121 cases of measles in 17 states between Jan. 1 and Feb. 6, most stemming from the California outbreak.

Earlier this month, a U.S. House subcommittee chaired by Pennsylvania Congressman Tim Murphy, R-18, held hearings on whether children should be vaccinated.

At the hearing, Murphy, who holds a doctoral degree in child psychology, said mercury is not used in the vaccines. That was a concern because people thought it caused autism, thanks to a now discredited 1990 study by a British physician who has since lost his medical license.

The testimony included that of National Center for Immunization and Respiratory Diseases Director Dr. Anne Schuchat.

"Vaccines save lives and are the best way for parents to protect their children from vaccine-preventable diseases," she said.

Measles was declared eradicated in 2000 due to the introduction of the vaccine, which became widely available in 1963. That year, 500 of the 3 million or 4 million people who got measles died.

Since then, the incidence dropped by 98 percent. By 1983, a record low of 1,497 cases were reported.

But then, parents became either complacent or wary and the numbers again grew. Between 1989 and 1991, there were a total of 55,622 cases, with 123 deaths.

In 1991, five unvaccinated children in Philadelphia died from the disease.

Health officials mounted a public education campaign, and the numbers again dropped, hitting a low of 37 in 2004.

New outbreaks

But after the now-debunked British study, and the pronouncements of celebrities who claimed vaccines cause autism, cases are again on the rise.

In Pennsylvania, there has been only one case, in Cumberland County. After it was confirmed, the state Department of Health set up a vaccination clinic and inoculated 300 people, containing an outbreak.

While all school-age children – public, private, charter, cyber or home-schooled – are required to be vaccinated in Pennsylvania, there are exemptions for religious, medical and moral or philosophical grounds.

Medical exemptions must be verified by a doctor; religious, moral or philosophical exemptions must be explained in writing by parents or guardians.

Some parents in California are having "measles parties" to deliberately expose their unvaccinated children to the disease, according to news reports. If the children contract measles, they will become immune. The California Department of Public Health is discouraging parents from the practice.

Unvaccinated children may be removed from school during outbreaks, but it's up to the districts to make that call.

Eighty-seven percent of kindergarten students in Pennsylvania are vaccinated, a low rate. But the figure reaches about 97 percent by seventh grade. A rate of 95 percent must be achieved to prevent outbreaks.