Assessing the Number of Vaccines Received Per Visit and Frequency of Vaccination Visits among Fully Vaccinated and Partially Vaccinated Children 16-19 Months of Age, IIS Sentinel Sites, 2004-2008

Background:
The addition of new vaccines, such as rotavirus and hepatitis A, to the ACIP-recommended schedule may increase the number of vaccination visits.

Objectives:
Measure the impact of the addition of rotavirus and HepA to the ACIP-recommended vaccine schedule on the number of antigens received per visit and the frequency of vaccination visits by 16 months of age.

Methods:
Data from 8 IIS sentinel sites were used to determine the number of antigens administered by age group and well-child visit, and the number of vaccination visits by age group and vaccination status (partially or fully vaccinated) for two cohorts of 16-19 month olds. Children in cohort 1 (born 8/1/2004-11/30/2004) were considered fully vaccinated with 3 doses DTP, 2 polio, 1 MMR, 3 Hib, 2 HepB, 4 PCV, and 1 varicella. Children in cohort 2 (born 8/1/2006-11/30/2006) were considered fully vaccinated if they received the same vaccines in Cohort 1 plus 3 doses of rotavirus vaccine and 1 dose HepA.

Results:
The average percentage of fully vaccinated children fell from 42.5% in Cohort 1 to 14.3% in Cohort 2. However, the percent of fully vaccinated children remained the same when the Cohort 1 fully vaccinated definition was applied to both cohorts. The average number of antigens administered per visit increased by one antigen at the 2, 4, 6, and 12 month well-child visits from Cohort 1 to Cohort 2. In both cohorts, most fully-vaccinated children received all vaccinations within 5-6 visits.

Conclusions:
Rotavirus and HepA did not increase the number of vaccination visits for children who became fully-vaccinated. Data suggest that children received on average one additional antigen per vaccination visit during their first year. The decrease in fully vaccinated children in the more recent birth cohort was likely due to children not receiving newly recommended vaccines on time rather than affecting previously recommended vaccines.