Measles is making a comeback and that is prompting public figures, health officials, and parents of vaccinated children to speak out.

The United States is headed for its worst outbreak of measles in decades.

And that’s causing some backlash from people whose children are vaccinated, as well as public statements from societal leaders in support of vaccines.

The Centers for Disease Control and Prevention (CDC) reported 102 cases of measles from Jan. 1 to Jan. 30. The country is on track for the worst year of measles since 1994, when 958 cases were reported.

The truth about the MMR vaccine »

The situation prompted President Obama in an interview on the “Today” show to urge people to get vaccines.

“I understand that there are families that in some cases are concerned about the effect of vaccinations,” the president said. “The science is, you know, pretty indisputable. We’ve looked at this again and again. There is every reason to get vaccinated, but there aren’t reasons to not.”

Dr. Sandy Hassink, president of the American Academy of Pediatrics, had a similar message in a statement released Monday.

“The American Academy of Pediatrics strongly urges parents to make sure their children have received the measles, mumps and rubella (MMR) vaccine,” she said. “While it is best to get the vaccine as soon as your child reaches the recommended age, it is never too late to get your children caught up so they can receive the vaccine and be fully protected.”

The outbreak has caused some parents in California to demand that the state Legislature toughen the laws concerning vaccinations, according to a story in the San Jose Mercury News.

California is one of 19 states in the country that allow exemptions to childhood vaccinations simply due to personal beliefs. Another 29 states allow some sort of personal exemption. Mississippi and West Virginia have the toughest requirements, allowing exemptions only for medical reasons.

The outbreak started in December at two Disneyland parks in Southern California. The CDC reported the disease was probably imported from the Philippines.

Measles is back, health officials say, because a growing number of parents are refusing to have their children vaccinated.

What does measles look like? »

The Disney outbreak is “100 percent connected” to parents who refuse vaccination, said Dr. James Cherry, a pediatric infectious disease specialist at UCLA.

“It wouldn’t have happened otherwise. It wouldn’t have gone anywhere,” he told the New York Times. “There are some pretty dumb people out there.”

Melinda Gates, co-founder of the Bill and Melinda Gates Foundation, put it more gently.

“We take vaccines for granted in the United States,” she told the Huffington Post. “Women in the developing world know the power of [vaccines]. They will walk 10 kilometers in the heat with their child and line up to get a vaccine because they have seen death. We’ve forgotten what measles deaths look like.”

The anti-vaccine movement was fueled by a 1998 study in The Lancet. A British gastroenterologist, Andrew Wakefield, said the measles vaccine caused chronic inflammation of the colon and autism.

The paper was determined to be a fraud, based on false data, and paid for by anti-vaccination groups. Dr. Wakefield was banned in 2010 from practicing medicine in the United Kingdom. The Lancet retracted the article that same year.

Health experts agree no medication is 100 percent effective or 100 percent safe. That includes the two measles vaccines approved for use in the United States — MMR (measles, mumps and rubella) and MMRV (measles, mumps, rubella and varicella).

Nonetheless, measles vaccinations are more than 95 percent effective. Up to 10 percent of people who receive the vaccine develop only a low-grade fever and a mild rash.

The American Academy of Pediatrics said there are no safety studies that show any link between measles vaccine and other health problems.

Measles used to be one of those childhood diseases like chicken pox or whooping cough that everyone got in the 1950s and early 1960s. The CDC said more than 3 million Americans contracted measles every year and 400 to 500 died from it. That changed when the first measles vaccine was released in 1963.

After the measles vaccine was released, the number of cases plunged. In 2000, measles was declared eradicated from the United States. There were about 60 cases every year, mostly people who got measles while traveling outside the country. But measles didn’t spread because so many people in the United States were vaccinated.

The idea is called “herd immunity” or “community immunity.” When enough people are immunized, the disease has difficulty spreading.

Community immunity is especially important in diseases like measles. It is one of the most contagious diseases known. Without vaccination, about 90 percent of people exposed to measles will get the disease.

There are people who should not get the measles vaccine. That includes infants younger than 12 months and anyone with an immune system that has been weakened by diseases such as HIV and cancer or by drugs such as high-dose steroids.

Community immunity protects those who are the most likely to get measles and the most likely to die from it.

Measles seldom kills directly. In populations with elevated levels of malnutrition and inadequate healthcare, up to 10 percent of people who get measles die. Complications associated with measles include encephalitis (an infection that causes brain swelling), dehydration, and severe respiratory infections such as pneumonia. Even if measles doesn’t kill, it can still cause blindness and other lifelong problems.

“This outbreak is the poster child of why we need to immunize,” said Dr. David Kimberlin, president of the Pediatric Infectious Diseases Society and professor of pediatrics at the University of Alabama at Birmingham. “There will be a major measles epidemic unless something changes. People do not take lifesaving opportunities and it’s our children who end up paying the price.”