John F. Enders is likely turning in his grave.

Massachusetts in April reported this year’s first case of the measles, for which Enders created a vaccination more than 50 years ago. The deadly virus is making a comeback across the United States.

“There is heightened concern,” said Dr. Lawrence Madoff, director of the Epidemiology and Immunization Division at the Massachusetts Department of Public Health. “The United States is seeing hundreds of cases this year – way above normal levels.”

The U.S. Centers for Disease Control and Prevention in March said 387 measles cases were reported in 15 states, already exceeding the total from 2018. Massachusetts joined the list on April 1 when state officials reported the first case of 2019, and warned residents of potential exposure in multiple locations, including Braintree, Framingham, Hyannis, Plymouth and Waltham.

Measles is a disease caused by a virus resulting in fever and a red skin rash that spreads more easily than most other illnesses. The virus lives in the nose and throat and is sprayed into the air when an infected person sneezes or coughs. It can stay in the air for up to two hours.

The resurgence of the measles virus since the U.S. announced its elimination in 2000 — meaning no cases of transmission for a one-year period — is concerning to the medical community, but not entirely surprising.

Vaccinations, including the one to prevent measles, have come under fire in recent years. Opposition groups, sometimes called “anti-vaxxers,” claim vaccinations are potentially harmful, and can be linked to rising rates of chronic-health conditions and developmental disabilities such as autism spectrum disorder.

“It is our belief that these rates will continue to increase if parents are not aware of the unhealthy choices in their lifestyle such as industrial processed foods, side effects of vaccine choices and other environmental and lifestyle factors,” Health Choice Massachusetts wrote on its website.

The nonprofit, an affiliate of Minnesota-based American Citizens for Health Choice, is one of many organizations across the country promoting anti-vaccination information. The group, which did not respond to a request for comment, regularly posts articles and flyers about the potential harm of vaccinations to Facebook. The group has more than 1,000 likes and followers, respectively.

The anti-vaccination sentiment — which has mounted support in pockets across the country — contradicts what most medical doctors agree on: Vaccinations are safe and effective.

“They’re clearly one of the best health tools that we have, so of course we do our best to combat misinformation,” Madoff said.

In some ways, he argues, the success of vaccinations makes it even harder to promote the importance of inoculation. Before Enders created his vaccination in the 1960s, the measles killed roughly 450 U.S. residents and hospitalized another 48,000 each year. Today, most Americans are unfamiliar with the illness.

“Most people in the United States have never seen a case,” Madoff said.

The campaign against vaccinations has worked well in many states, and many in the medical community say its success has contributed to the comeback of measles, including six outbreaks this year in California, New Jersey, New York and California. An outbreak is defined as three or more cases.

Social media is one way anti-vaccination messaging reaches more people and its impact has been studied. In 2017, a group of researchers turned to Twitter to try and understand the demographics behind communities with anti-vaccine beliefs.

The group analyzed more than half a million tweets between 2009-2015, and found the sentiment was most common among women who recently gave birth, along with households with high income levels, men aged 40-44 years old and men with minimal college education, according to the study.

The research also found the highest frequency of such tweets happened in five states, including Massachusetts. The group, which published the work in Social Science & Medicine, determined the information could help public-health officials target anti-vaccination sentiment.

“Real-time interventions are needed to counter anti-vaccination beliefs online,” according to the report. “Identifying clusters of anti-vaccination beliefs can help public health professionals disseminate targeted-tailored interventions to geographic locations and demographic sectors of the population.”

Dr. Alain A. Chaoui, a family physician at Congenial Healthcare with offices in Lynn, Middleton, Peabody and Wakefield, says he works hard to change the minds of pregnant women who are skeptical about vaccinating their children. Chaoui, a Boxford resident, says increasingly the question comes up.

“Unfortunately, I do hear about it a lot and I see it talked about on social media. This is very dangerous. People need to understand how preventable these diseases are,” said Chaoui, who also serves as president of the Massachusetts Medical Society.

Despite the high rate of anti-vaccination discussion online in Massachusetts, the state boasts 97 percent coverage when it comes to measles vaccinations for kindergarteners. According to the CDC, Mississippi has the highest coverage for all vaccinations with 99.4 percent. Washington D.C. is the lowest with 81.3 percent. In the Bay State, the coverage is so high in part because parents are required to provide proof of vaccinations before their children can enter the school system.

But there are two exceptions to the rule.

The first is a medical exemption, which is allowable if a physician determines a patient is not healthy enough for certain vaccinations. The second is a religious exemption and the qualifying factors are much more nuanced.

“In the absence of an emergency or epidemic of disease declared by the department of public health, no child whose parent or guardian states in writing that vaccination or immunization conflicts with his sincere religious beliefs shall be required to present said physician’s certificate in order to be admitted to school,” according to Massachusetts general laws.

In some cases, parents have taken advantage of the exemption and reportedly faked religious beliefs to avoid vaccinating their children. Religious exemptions are highest on the islands and the western part of the state.

In New York, a sharp rise in religious exemptions between 2000 and 2011 pushed lawmakers to establish more rigorous guidelines, which could become more common if outbreaks continue to happen, according to a 2016 study published in The Journal of Pediatric Pharmacology and Therapeutics.

“These burdens of proof are likely to become more popular as an increasing number of parents attempt to use the nebulous loophole of religious freedom to bypass the societal necessity of combating preventable diseases through immunizations,” according to the study.

The American Medical Association would like to completely do away with non-medical exemptions.

“The AMA strongly supports legislation that eliminates non-medical exemptions from immunizations, and we will continue to actively urge policymakers to eliminate non-medical exemptions from immunizations,” said Dr. Barbara L. McAneny, AMA president.

The number of religious exemptions is relatively miniscule in Massachusetts, but has increased during the last decade. In the 2007-08 school year, 779 kindergarteners – representing 0.6 percent – claimed religious exemptions, according to the state. By 2017-18, the number increased to 853, or 1.1 percent of kindergartners in the Bay State. A similar trend is realized among 7th graders, although the trend appears to be leveling off.

The medical community, including Madoff, says under-vaccinated communities are concerning because once an illness happens to one person, the likeliness of it spreading increases. It happened in 2011 when 24 cases of measles were reported.

“There are always some pockets where we’re waiting for the match to hit the gasoline,” he said.

Eli Sherman is an investigative and in-depth reporter at Wicked Local and GateHouse Media. Email him at esherman@wickedlocal.com, or follow him on Twitter @Eli_Sherman.