(CNN) Facebook is looking into suppressing certain anti-vaccine messaging on its social platform, a move that raises questions about free speech and public health.
"We've taken steps to reduce the distribution of health-related misinformation on Facebook, but we know we have more to do. We're currently working with outside experts on additional changes that we'll be announcing soon," a representative for the social media giant said Friday.
In recent years, anti-vaccination groups have been vocal on Facebook, frequently sharing and posting information against vaccines and their safety. At the same time, there has been a rise in cases of measles and other infectious diseases across the United States.
On Thursday, House Intelligence Committee Chairman Adam Schiff wrote open letters to Facebook CEO Mark Zuckerberg and Google CEO Sundar Pichai about his concern that the technology companies are allowing the spread of anti-vaccine misinformation.
He wrote to Zuckerberg, "Facebook and Instagram are surfacing and recommending messages that discourage parents from vaccinating their children, a direct threat to public health, and reversing progress made in tackling vaccine-preventable diseases."
That open letter went on to ask Zuckerberg whether distributing medically inaccurate information about vaccines violated the social media platform's terms of service and whether Facebook accepts paid advertising from anti-vaccine activists, among other questions.
"There is no evidence to suggest that vaccines cause life-threatening or disabling diseases, and the dissemination of unfounded and debunked theories about the dangers of vaccinations pose a great risk to public health," Schiff wrote.
Google, which also owns YouTube, had no direct response to the letters but noted that YouTube has worked to improve recommendations regarding content.
Schiff's letter noted that he "was pleased" to see YouTube's announcement in January that it would no longer recommend videos that violate its community guidelines, including "content that could misinform users in harmful ways," according to the announcement.
Now, it seems, Facebook has entered the vaccine battle as it mulls the distribution of anti-vaccination messaging on its platform.
Arthur Caplan, a professor and founding head of the Division of Medical Ethics at NYU Langone Health in New York, said that he is "very supportive" of Facebook's new efforts to police anti-vaccine messaging.
"They don't have to be a platform for lying, for fearmongering, for inaccuracy, especially when children are put at risk," said Caplan, who has written about anti-vaccination groups' social media presence in the journal Human Vaccines & Immunotherapeutics.
"I'm not trying to say that somebody can't take positions against vaccines on Facebook," he said. "I know people are going to say this is an intrusion into free speech -- many anti-vaxxers will say that -- but no one is saying you can't be anti-vaccination. What we're saying is, you can't lie. You can't fearmonger."
In the state of Washington, a measles outbreak in Clark County, just north of Portland, Oregon, has been officially declared a state of emergency. At least 58 people have been infected since the outbreak began in January, according to state and local health officials.
"It is exquisitely contagious," said Dr. Alan Melnick, director of the county health department. "You can be in a room where somebody with measles had left two hours earlier and still get the disease."
Measles kills about 2 of every 1,000 children infected, he said. "The thing that keeps me up at night is having a death, you know, a child die from this."
Washington lawmakers are now weighing a bill, House Bill 1638, that would tighten the state's vaccination rules, according to CNN affiliate KOIN.
Vaccination rates in Clark County are low partly because Washington allows parents to opt out of vaccinating their children, not only for medical and religious reasons but for "philosophical" and "personal" ones. Lawmakers are debating removing those provisions for the measles, mumps and rubella vaccine.
"Hundreds of thousands of people in my community have been involved in this issue and have lent support to this bill," Rep. Paul Harris told the State Assembly last week. He represents Clark County and is sponsoring the legislation.
"They're concerned about our community, its immunity and the community safety."
Bernadette Pajer, co-president of the advocacy group Informed Choice Washington, which opposes mandatory vaccination, told CNN affiliate KOIN that the bill "takes away our freedom."
Anti-vaccination activists protested outside the State Assembly during a hearing on the bill last week.