The U.S. childhood immunization schedule, the grid of colored bars pediatricians share with parents, recommends a set of vaccines given from birth through adolescence to prevent a range of serious infections. The basic structure has been in place since 1995, when federal health officials and medical organizations first issued a unified national standard, though new vaccines have been added regularly as science advanced.
Vaccines on the childhood schedule have been tested in controlled trials involving millions of participants, and they are continuously monitored for safety after being rolled out. The schedule represents the accumulated knowledge of decades of research. It has made the diseases it targets so rare that many parents have never seen them.
But the schedule is now under scrutiny.