A new study finds nearly half of the babies and toddlers in the United States aren't receiving their recommended vaccines on time. The study from Kaiser Permanente Colorado in Denver found that over 54% of children were late on at least one of their vaccines for serious health issues including measles, mumps, rubella, tetanus and whooping cough. Officials behind the study say there are real concerns that such diseases could make a return to outbreak status due to more and more children being under vaccinated. They say whole communities and schools could be vulnerable to outbreaks.