The World Health Organization, which the Trump administration withdrew from early this year, estimates that for every person infected with measles, 18 secondary infections are likely to result — meaning that schools could soon see an exponential growth in measles cases. Yet instead of sending out additional teams of specialists to encourage vaccinations in places such as Lancaster County, the CDC’s leadership is bowing to political pressures to trash-talk the Pennsylvania public health system and dismiss the seriousness of an outbreak that, nationally, has seen more measles cases and deaths in the past two years than in the preceding quarter century.