“If you have to get sick,” Marcia Brady bellows. “Sure can’t beat the measles!” Marcia delivered the line in an episode of The Brady Bunch that aired in 1969. Fifty years later, it's echoing through Facebook antivaxxer communities.

If you ignore the sitcom context, it does sound like a peppy mid-century advertising slogan for the disease, the sort of thing a feverish Don Draper might have come up with after his eighth Old Fashioned. So, naturally, that’s how antivaxxers are taking it.

Emma Grey Ellis covers memes, trolls, and other elements of internet culture for WIRED.

Marcia’s pro-measles platform has been a staple of the antivax community for a while now—it’s a popular meme, which means that it’s also T-shirt. Screengrabs of blonde-pigtailed Marcia grinning at the thought of measles are so common in anti-vaccine forums that Maureen McCormick, who played Marcia, got on NPR and asked to be excluded from this narrative. She’s quaintly scandalized that strangers would use her face for their own ends without her permission, without asking her whether she believes in vaccines or not. The antivaxxers do not care.

To them, whether or not Maureen McCormick vaccinated her children, which she did, is irrelevant, as is McCormicks’ discomfort with becoming the face of measles. (“Boo hoo,” read several Facebook comments.) So is the fact that the creator of The Brady Bunch, Sherwood Schwartz, was also a known child vaccinator. Everyone involved can wave their vaccination records all they want and it won’t deter anybody from buying a T-shirt that informs the world that the titular family of a sitcom failed to die of measles on daytime television. This meme is not about Marcia or any of the Brady bunch: It’s about having a slice of 1969.

For antivaxxers, the episode serves as a time capsule from an era when measles was still a common childhood illness. Because getting and spreading the measles is a goofy, single-episode plotline in a cheery sitcom, the logic goes, measles outbreaks must not have been feared in the 1960s, so they shouldn’t be today.

That’s not necessarily faulty reasoning. Sitcoms are a terrible source for medical advice, but they do reflect the mainstream concerns and attitudes of their time. Clearly your kid catching measles was lower on the hierarchy of parenting worries back then. But it’s not because measles ain’t so bad. It’s probably because 1960s parents were expending their energy fretting over worse diseases like polio and smallpox and the bubonic plague. Also, The Bed-Bound Adventures of Miserable Rashy Children sounds like a terrible TV show.

Trouble is, when antivaxxers watch the measles episode of The Brady Bunch, they’re not seeing a sitcom in which the children will inevitably learn that infecting themselves with measles to avoid school was a bad decision. They’re seeing an infomercial for an acceptable plague that was a laughing matter just half a century ago. And then they bring Braxton over to Jaxon’s house so the boys can cough in each other’s face. In doing so, antivaxxer parents are dooming their kids to life in a medical 1960s that never actually existed because it’s conjured out of a single piece of fiction, puffed up with third-hand nostalgia and stubborn self-fulfilling prophecy. But screw the facts, they’re Making Marcia Measley Again.

More Great WIRED Stories