Cases of once nearly-eliminated diseases measles and pertussis (aka “whooping cough”) have risen in the U.S., and researchers are pointing the blame at anti-vaccination attitudes.

In a new JAMA study funded by the National Institutes of Health, scientists from Emory and Johns Hopkins Universities directly linked the rise in measles cases in the U.S. to vaccination refusal. They also found a strong connection between pertussis cases and refusals to vaccinate.

Measles cases have been on the rise in the U.S. over the last few years, according to data from the Centers for Disease Control and Prevention, and the majority of people who contracted the disease were unvaccinated. In 2012, there were 55 reported cases of the disease, but in 2014 there were 667 cases, followed by 189 in 2015 (145 of which were linked to the Disneyland outbreak in early 2015).

According to CDC data, 32,971 cases of pertussis were reported in 2014—a 15 percent increase over the number of cases reported in 2013.

For the study, researchers analyzed separate studies done on measles and pertussis outbreaks, which described 1,416 measles case and 10,609 pertussis cases. Of the 970 measles cases that had vaccination data, 574 were unvaccinated despite being eligible and 405 were unvaccinated due to non-medical exemptions (such as religious or philosophical reasons).

For the pertussis cases, up to 45 percent of the largest outbreaks happened among unvaccinated or under-vaccinated people. However, several outbreaks also happened among people who were vaccinated “indicating waning immunity,” researchers wrote.

Board-certified infectious disease specialist Amesh A. Adalja, M.D., an assistant professor at the University of Pittsburgh Medical Center, tells SELF that he isn’t surprised by the findings. “The last two years were big years for measles,” he says. “We got an understanding of how bad the vaccination problem has become in the U.S.”

Measles cases have largely sprung up in specific geographic areas where anti-vaccination attitudes and actions run high, he points out.

However, Adalja calls the increase in pertussis cases “more complex.” “There was a change in the formulation of the vaccination,” he explains. “We’ve seen breakthrough cases as a result.” According to Adalja, the new vaccine, known as DTaP (Diphtheria, tetanus, and pertussis vaccine) came into favor after people had concerns that the previous vaccine, DTP, might cause encephalitis, an inflammation of the brain. “The anti-vaccine attitude is responsible for that indirectly because they had a lot of misgivings about the DTP vaccine,” he says. “People switched from the DTP to the DTaP, which gives a less strong immunity. And, on top of that, there are people who are not vaccinated.”

Martin Hirsch, M.D., professor of medicine at Harvard Medical School and a senior physician in the infectious disease unit at Massachusetts General Hospital, points out that the refusal to vaccinate affects more than just the patient. "People who are unvaccinated are potentially a risk to not only themselves but to others in the community," he tells SELF, adding that any increase in measles and pertussis cases is "a worrisome thing."

The danger in contracting these illnesses is that they’re often difficult to treat, Lawrence M. Dell, M.D., internal medicine specialist and cofounder of Michigan’s Lakes Urgent Care, tells SELF. “Pertussis is typically referred to as a 100-day cough, and it can be really severe,” he says, adding that it can even kill people (newborns are especially at risk). Plus, he notes, some people end up going through various trials of treatment and misdiagnoses before doctors even figure out that it’s whooping cough. There can also be after-effects of the disease. “There can be a residual persistent cough or shortness of breath,” Dell says.

For measles, which Adalja calls “one of the most contagious diseases on the planet,” people typically have to just wait it out.

While Dell says we can get these diseases under control by increasing vaccination rates, he also expects that we’ll see more outbreaks first.

Adalja is hopeful that news of these outbreaks as well as the latest study will help more people vaccinate their children. “There are always going to be people who hold out against it,” he says. “But the measles outbreak in Disneyland got a lot of people to rethink their opposition to vaccines. Hopefully now more will do the same.”

Photo Credit: Kkgas / Stocksy