A bit of a long read.

They came from across North America, paying $200 each to attend the ritzy event in Washington, D.C., hoping to snag selfies with some of the biggest names in the anti-vaccination movement.

For the anti-vaccination activists gathered in the U.S. capital last November, it was also a chance to strategize on ways to further their cause.

And they were more than willing to share those strategies with the undercover Marketplace journalists who attended the event, posing as activists trying to grow the movement in Canada.

The Marketplace investigation provided a rare glimpse into the inner workings of the anti-vaxx movement, which experts say is largely to blame for a shift in mindset about vaccination. Nearly half of Canadians today have some concern about vaccine safety.

"Take vaccines out of the name — that way you won't get flagged," said one Virginian woman attending the event.

She was speaking about how to get around social media filters geared at weeding out anti-vaccination content.

The woman also pointed to another popular tactic: Challenging vaccination policies under the seemingly libertarian banner of "health freedom," "medical freedom," or "informed consent."

Her own group is named Virginians for Informed Consent and has about 1,200 members.

She's also gone a step further, making the group almost impossible for the public to find.

"We're secret," she said. "You can't search our name [on Facebook].

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