The CDC recommends a schedule of vaccines for young children, including the following. Most of these vaccines require multiple doses by age 3. In past years, the majority of U.S. children ages 19 months to 3 years have been vaccinated.
CDC vaccination coverage data for children ages 19 months to 3 years are based on telephone interviews with parents and surveys of immunization providers. 2017 is the CDC's latest published data. Haemophilus influenzae type b requires 3 or 4 doses depending on the formulation.