For the first time, US doctors have found a fully vaccinated person who transmitted measles to other people, Science reports. Now dubbed "Measles Mary," the 22-year-old theater worker in New York City had been released without quarantine because she was fully vaccinated. Then four people she'd interacted with got sick—including, oddly enough, two who had been vaccinated and two who showed signs of earlier measles exposure, which should have protected them. In Measles Mary's case, her vaccine-given immunity had apparently declined.
We all have natural IgM antibodies that protect us from microbial invasions, if imperfectly; a full vaccination or case of the measles should buttress that with stronger IgG antibodies. But an investigation found that Mary's IgG antibodies had lost their power to fight off measles. The prospect of waning measles immunity is unnerving as the disease makes a comeback in major US cities, Science notes. There were only 189 reported cases last year, reports The Week, but even a low failure rate could devastate a large high school, according to a vaccination expert. Still, he said, the worst failures occur "when people refuse the vaccine in the first place."