The recent rise in measles and whooping cough (pertussis) cases in the United States is being driven by people who are unvaccinated or under vaccinated.

That’s what researchers concluded in a study published today in the Journal of the American Medical Association (JAMA).

The researchers focused on measles cases. Measles, along with pertussis, were officially considered eradicated in the United States in 2000. Rates for both diseases were at the lowest point for U.S. incidence in 1977.

After analyzing previously published research, the study authors estimated that more than half of people who contracted measles had not been vaccinated against the disease.

rise in measles

The researchers also said anywhere from 24 to 45 percent of people who came down with pertussis were either unvaccinated or under vaccinated.

That’s despite the fact that less than 1 percent of parents do not vaccinate their children, according to the Centers for Disease Control and Prevention (CDC).

The study authors said in a statement that the research shows greater emphasis needs to be placed on the association between vaccine refusal and the increase in these diseases.

“This review has broad implications for vaccine practice and policy,” the authors wrote. “For instance, fundamental to the strength and legitimacy of justifications to override parental decisions to refuse a vaccine for their child is a clear demonstration that the risks and harms to the child of remaining unimmunized are substantial.”

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Looking at the Numbers

The researchers looked at 18 published measles studies for their report.

They uncovered 1,416 measles cases in patients from 2 weeks to 84 years of age. 57 percent had no history of measles vaccinations.

Detailed immunization records for 970 measles cases were reviewed. Of these cases, 574 were eligible to have vaccines, and 71 percent of the patients skipped inoculation for nonmedical reasons.

The researchers also looked at 32 reports of pertussis outbreaks. More than 10,000 of these cases had information on vaccination status. The age range was 10 days to 87 years of age.

In the five largest statewide epidemics, the researchers said, anywhere from 24 to 45 percent of pertussis patients were not inoculated against the illness.

Several pertussis outbreaks, however, occurred in highly vaccinated regions. The researchers suggested these epidemics were caused by decreased immunity among the population.

CDC officials said outbreaks generally happen in clusters.

“While coverage rates are high nationally, locally there may be clusters of under vaccinated or unvaccinated children that put those children, their schools, and communities at risk for outbreaks,” the CDC stated in an email to Healthline.

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Community Immunity

The rising number of cases is particularly serious for people who can’t be vaccinated for medical reasons. That includes children who are undergoing cancer treatment.

Researchers also noted that no vaccine is 100 percent effective.

The CDC estimates that about 3 percent of people who have the recommended doses of measles vaccines will still get the disease.

They also estimate 2 percent of those who’ve received the pertussis vaccine will come down with that illness.

The study authors highlighted a December 2014 outbreak of measles that originated in Disneyland in Southern California. There were 111 measles cases. About half of the people affected were unvaccinated.

Researchers also noted that rates of nonmedical exemptions for vaccines have increased steadily the past 20 years. The initial increase was mostly seen in states with more personal belief exemptions. However, they noted, the rise is now also seen in states with moderately difficult exemption procedures.

They said potential policies to combat the rise in exemptions include school-mandated immunization and increased difficulty obtaining exemptions.

CDC officials said the best preventative measure is for parents to make sure their children have a full slate of vaccinations. These vaccinations will protect them from 14 serious illnesses.

“Following the recommended immunization schedule protects as many children as possible, before they are exposed to potentially life-threatening diseases,” the CDC said in its email.

The CDC said a team effort is needed to improve vaccination coverage. Health professionals, school officials, government officials, and parents need to be involved.

As part of this effort, the study authors said, the concerns of vaccination opponents need to be addressed.

“At the same time, immunization policy makers must also address the reasons for vaccine hesitancy, which may include parental perceptions regarding the risk and severity of vaccine-preventable diseases, the safety and effectiveness of routine immunizations, and confidence in medical professionals, corporations, and the healthcare system,” the authors wrote.

Read More: Gaps in Vaccinations Leave 1 in 8 Children at Risk of Measles »