Oh that’s where all the anti-vaxxing is coming from.

In 2008, Vaccinate Your Family, the nation’s largest nonprofit dedicated to advocating for vaccinations, had to stop posting videos to YouTube.

Then known as Every Child By Two, the organization had used its channel on the massive video platform to post interviews with doctors, public service announcements and testimonials from parents of children who had died of vaccine-preventable diseases.

But those messages were quickly sabotaged. YouTube’s recommendation system, which appears alongside videos and suggests what users should watch next, would direct viewers to anti-vaccination videos, according to Amy Pisani, executive director of Vaccinate Your Family.

Yes, it’s The American Way. You’ve read /listened to /watched something reasonable and evidence-based, now wouldn’t you like to read or watch something cracked and evidence-free and just made up out of somebody’s empty head? Of course you would! Here are four to choose from.

Pisani’s story offers a window into the struggle that public health officials and advocates face as they attempt to provide information on vaccinations on social media, where anti-vaccination proponents have spent more than a decade building audiences and developing strategies that ensure they appear high in search results and automated recommendations.

Because when in doubt, try to get epidemics going again!

After more than a decade and facing mounting pressure, YouTube announced a change in its recommendation algorithm this month, saying it would stop suggesting conspiracy videos like the ones that followed Vaccinate Your Family’s. YouTube also stopped some anti-vaccine videos from showing ads and earning money, and started providing more information about the threat of vaccine hesitancy in a window below anti-vaccine videos.

In a statement to NBC News, a YouTube spokesman called misinformation around medical topics “a difficult challenge,” and referred to their recent policy changes, adding, “like many algorithmic changes, these efforts will be gradual and will get more and more accurate over time.”

No worries. It’s not as avoiding epidemics is a big deal or anything.

And on social media, the anti-vaccination proponents seem to be winning.

Vaccinate Your Family’s Facebook page has nearly 200,000 likes and followers, but nowhere near the visibility or engagement of anti-vaccine pages and private groups, where hundreds of thousands of users post articles from fringe health websites, trade tips on avoiding state-mandated vaccinations, and share memes bashing parents who vaccinate.

But Team Anti-epidemics is getting better at pushing back.

Stephan Neidenbach, 38, a middle-school technology teacher from Annapolis, Maryland, runs “We Love GMOs and Vaccines,” a Facebook page he started in 2014, he said, to combat growing misinformation on Facebook.

At first Neidenbach said he was just anonymously replying to anti-vaccine content, but soon scientists, farmers and doctors started following the page and sharing.

The page — now with with 194,000 followers — is one of several on Facebook that respond directly and in-kind to anti-vaccination pages. Users share news reports about vaccine outbreaks, and post memes and screenshots of posts from anti-vaccine groups, which they ridicule in the comments.

One recent post read, “If you’re antivaxx and you see me making fun of antivaxx people, I just want to say that I am talking about you personally and I hope you’re offended because you’re fucking stupid.”

“That’s what separates me from other organizations,” Neidenbach said. “I’m not an organization, and I’m not trying to run a nonprofit. I’m just a school teacher. And I don’t have to be as nice as I do in the classroom.”

“They have to worry about being professional,” he said. “But we can do more inflammatory stuff that the World Health organization can’t do. And the inflammatory stuff, as you can tell by the anti-vaxxers, does well on Facebook.”

When it’s anti-epidemic it’s in a good cause.