"I just remember being very scared."
That's how Lydia, a 39-year-old mother of three in Canada, describes feeling when she was pregnant in 2008 with her daughter and had questions about vaccinating. She worried it might cause more harm than good.
"I remember feeling some trepidation and saying to my husband, 'We can't undo this once we do it,' " she says. NPR is not using Lydia's full name because she's worried about backlash from a community she once believed in — people opposed to vaccines.