evidence: For such parents, emotional descriptions of children who have allegedly been injured by vaccines may prove more persuasive than tales of half-forgotten diseases. "My wife ran the intensive care unit at a major teaching hospital in America, and she's never seen a case of measles or tetanus," says Berkley. "I think that's a big factor." He points out that vaccines are generally embraced in the developing world, where these diseases remain all too real — the WHO estimates that 158,000 people died from measles in 2011. "In general, people there desperately want vaccines and will walk for a day to get them," he says. But in nations with long-standing vaccination programmes, such as the United States or United Kingdom, it's easy to dismiss these diseases as harmless unless you've experienced the potential complications, which include pneumonia and encephalitis. "When I've talked with parents of unvaccinated children who have been admitted to hospital with complications from pertussis or measles, they inevitably say, 'I never knew it could be this serious'," says Halsey.