CDC researchers added that these make the toddlers vulnerable to infectious diseases that are popping up in the United States.
Infectious diseases included measles, mumps, whooping cough and chicken pox.
CDC lead researcher Elizabeth Luman, PhD, tells Medline Plus that many children that are vaccinated received their shots too early or too close together which make it not effective.
The researchers examine the histories of vaccination of 17,500 children aged 19 and 35 months and considered the federal guidelines from the Advisory Committee on Immunization Practices (ACIP). The study revealed that 19% of children were missing one or more doses and 8% had received at least one invalid vaccination.
The study is published in the June issue of the American Journal of Preventive Medicine.
