KEYWORDS:
Immunization schedule, vaccination coverage

BACKGROUND:
Immunization coverage has dropped since 1999. Changes in immunization schedules may have contributed to this decline.

OBJECTIVE(S):
To document trends in vaccine administration relative to changes in the immunization schedule.

METHOD(S):
From 1996 to 2001, we conducted semi-annual chart audits of 22,515 randomly selected 6-35 month-olds at 26 inner city practices in New York City. We assessed immunization rates for 12-23 month-olds for DTaP, Polio, MMR, Hib and HepB (4:3:1:3:3), per ACIP. Quarterly, we calculated median age for each antigen dose (1995-2000).

RESULT(S):
MMR median age remained constant. Introduced in 1996, by 1998, age at receipt of varicella matched MMR’s and remained stable. The 1998 switch to DTaP, disuse of DTP/Hib and introduction of IPV/OPV were not associated with changes in age at vaccination. The 1999 switch to all IPV was associated with a delay of Polio3 by 2000. Also in 1999, the thimerosal scare and introduction of HepB-Hib were associated with delays of age at receipt for HepB1, HepB2, HepB3, Hib3, and Hib4 by 2000. The 2000 introduction of pneumoccocal conjugate was associated with delay in age of receipt for DTaP4. Compared to 1999, in 2000 significantly more children received DTaP4, Polio3, HepB3, and Hib3 late. CASA 4:3:1:3:3 coverage increased from 37% in 1996 to 56% in 1999, and then declined to 48% in 2000.

CONCLUSIONS(S):
In inner city practices in New York City, changes in the recommended immunization schedule were associated with delays in the age of administration of selected antigens, notably the last doses in the series. Changes in one antigen series affected the delivery of others. These delays had a negative impact on immunization coverage, which declined by 8% since 1999.

LEARNING OBJECTIVES:
To learn how changes in the immunization schedule affect the vaccination coverage.