As a measles outbreak continues to spread in Washington state, Facebook is “exploring additional measures” to fight false anti-vaccine content on the platform, Bloomberg reports.

The news comes on the heels of criticism from Representative Adam Schiff, who sent Facebook CEO Mark Zuckerberg a letter about vaccine misinformation on Facebook and Instagram today. In the letter, first reported by Bloomberg’s Sarah Frier, Schiff voiced concerns that both Facebook and Instagram serve up misleading, fear-mongering content about vaccines, which have been shown to be safe, effective, and critical for public health. Schiff also sent a similar letter to Google’s Sundar Pichai about vaccine misinformation on YouTube.

In the letters, Schiff wrote that the misinformation on these platforms could make parents ignore legitimate medical advice to vaccinate their children. “Repetition of information, even if false, can often be mistaken for accuracy,” he wrote. He referenced recent reporting by Julia Carrie Wong at The Guardian, who discovered that both Facebook and YouTube are full of fear-mongering, inaccurate anti-vaccine propaganda. What’s more, Wong found, YouTube’s recommendation algorithm helped lead people to those lies.

Schiff applauded YouTube for its recent move to start restricting recommendations for videos “that could misinform users in harmful ways,” which YouTube told The Guardian will include certain anti-vaccine videos. (Google declined to comment on the record to The Verge.) In July, YouTube announced that it will also link viewers to outside information “alongside videos on a small number of well-established historical and scientific topics that have often been subject to misinformation.” For example, YouTube links people to a Wikipedia page when they search for the MMR vaccine on the platform. Bloomberg points out, however, that anti-vaccination videos still rise to the top of YouTube’s search results for “vaccines.”

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In response to an inquiry about Schiff’s letter, a Facebook spokesperson told The Verge in an email: “We remove content that violates our Community Standards, downrank articles that might be misleading, and show third-party fact-checker articles to provide people with more context.” The company is “committed to accurate and useful information,” the spokesperson said. “We have more to do, and will continue efforts to provide educational information on important topics like health.”

The spokesperson did not immediately respond to a follow-up question asking for clarification about what those efforts might be. But a Facebook spokesperson told Bloomberg that they might include “reducing or removing this type of content from recommendations, including Groups You Should Join, and demoting it in search results, while also ensuring that higher quality and more authoritative information is available.”

In his letters, Schiff also asked both Google and Facebook heads for information about whether they’ve accepted money for anti-vaccine advertisements. According to the Daily Beast, anti-vaccine ads on Facebook have targeted demographics “most likely to include mothers,” including in Washington state where there is an ongoing measles outbreak. (Facebook did not immediately respond to a request for comment about the allegation.)

Vaccine misinformation is dangerous to more than just the kids whose parents voluntarily leave them unvaccinated — it’s dangerous to the community at large because it can encourage the spread of preventable, potentially deadly diseases like measles. While measles is known for causing a rash and a fever, the incredibly contagious virus can also cause pneumonia, brain damage, and death. People who aren’t able to receive the measles vaccine — including children under the age of 12 months — rely on everyone else being vaccinated to keep the virus at bay.

That’s why measles flare-ups like the one in Clark County, Washington, are so worrying, Peter Hotez, dean for the National School of Tropical Medicine at Baylor College of Medicine, told The Verge in January. “[Parents] have to live in fear of walking out with their infant into Walmart, or the public library.”