(CNN) Amid a significant rise in measles cases across the United States, lawmakers met in a congressional hearing on Capitol Hill on Wednesday to discuss what has been called " a growing public health threat ."

The House Committee on Energy and Commerce held the hearing, which included talks around response efforts for the current measles outbreak and where in the country vaccination rates of the recommended measles, mumps and rubella vaccine are found to be low.

"I do believe that parents' concerns about vaccines leads to undervaccination, and most of the cases that we're seeing are in unvaccinated communities," Dr. Nancy Messonnier, director of the National Center for Immunization and Respiratory Diseases at the US Centers for Disease Control and Prevention, said during the hearing

Nationally, the United States has high measles vaccination coverage.

"However, there are pockets of people who are vaccine-hesitant. ... Outbreaks of measles occur when measles gets into these communities of unvaccinated people," she said. "The only way to protect against measles is to get vaccinated."

America's climbing measles cases

Lawmakers discussed concerns around the spread of medically inaccurate information online relating to the measles vaccine -- and whether addressing that misinformation might be a way to stop outbreaks before they start.

For instance, Facebook has announced plans "to reduce the distribution of health-related misinformation" on its social media platform, a representative for the company said this month.

Around the same time measles cases have been rising nationwide, anti-vaccination groups have been vocal on Facebook, sharing and posting information against the safety of vaccines.

"I'm really concerned about the misinformation, but I also understand how complicated it is for parents," Messonnier said.

Even though there has been a small but slowly growing number of young unvaccinated children in the United States, CDC research shows that most parents continue to have confidence in the safety and effectiveness of the measles vaccine, Messonnier said.

She added that parents should talk to their children's pediatricians if they have any concerns.

Messonnier also noted that a lack of adequate access to health care can be a barrier to getting vaccinations, as has been seen in some rural and low-income communities.

Anti-vaccination content often claims that vaccines are unsafe -- such as that they can cause autism -- even though research has debunked such claims and the CDC points to its vaccine safety system to ensure that vaccines are as safe as possible.

The CDC website notes that common side effects of the MMR vaccine include a sore arm from the shot, fever, mild rash, and temporary pain and stiffness in the joints. Serious side effects, including allergic reactions and febrile seizures, are rare.

Messonnier said patients should talk to their doctor about their or their child's personal risk for rare side effects.

At one point during the hearing, anti-vaccination activists in the audience could be heard objecting to testimonies by Messonnier and Dr. Anthony Fauci, director of the US National Institute of Allergy and Infectious Diseases.

One woman in the audience raised an anti-vaccination book in the air. Another rubbed her fingers together, making the hand gesture for money.

'The sad thing is, this is a completely solvable problem'

The CDC recommends that children get two doses of MMR vaccine : the first dose at 12 through 15 months of age and the second at 4 through 6 years of age.

"You have one of the most contagious viruses known to man juxtaposed against one of the most effective vaccines we have," Fauci said at the hearing.

He added that there are two reasons why following vaccine recommendations remain important: "One, it is for the safety of your own child, and the other is a responsibility for your own community. ... We all have a responsibility to be part of that umbrella of herd immunity."

To achieve this for measles, the population immune needs to be 93% to 95% . "With measles, because it is so contagious, you have to have a herd immunity greater than 90%," said Dr. Robert Murphy, professor and director of the Center for Global Health at Northwestern University's Feinberg School of Medicine , who was not involved in Wednesday's hearing.

"That means that only 7 out of 100 people really would be at risk for getting measles. If somebody had measles, the likelihood that they would run into one of those seven is pretty low," he said, adding that in some communities facing measles outbreaks, herd immunity has dropped well below 93%.

"It's amazing that we actually have to have congressional hearings with what's going on today," said Murphy, who has treated children and adults with measles. "The sad thing is, this is a completely solvable problem, because we have a safe and very effective vaccine."

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Measles was declared eliminated in the United States in 2000, after a vaccination program. Elimination is defined by no continuous disease transmissions occurring for greater than 12 months.

Even though it has been declared eliminated in America, "measles continues to circulate globally, which means unvaccinated US travelers can be exposed to measles and bring it back home with them," Messonnier said at the hearing.