PEDIATRICS Vol. 111 No. 2 February 2003, pp. 296-301
Polio Extraimmunization in Children Younger Than 2 Years After Changes in
Immunization Recommendations
Loren K. Mell, BS*,,
Robert L. Davis, MD, MPH*,,
John P. Mullooly, PhD||, Steven B. Black, MD¶,
Henry R. Shinefield, MD¶, Kenneth M. Zangwill, MD#,
Joel I. Ward, MD#, S. Michael Marcy, MD**
and Robert T. Chen, MD
for the CDC Vaccine Safety Datalink Project
* Center for Health Studies, Group Health Cooperative, Seattle,
Washington University of
Chicago, Pritzker School of Medicine, Chicago, Illinois University of Washington,
Departments of Pediatrics and Epidemiology, Seattle, Washington || Center for Health Research, Northwest Kaiser Permanente, Portland,
Oregon ¶ Division of Research, Kaiser Permanente of Northern California,
Oakland, California # UCLA Center for Vaccine Research, Harbor-UCLA Medical Center,
Torrance, California ** Kaiser-UCLA Vaccine Research Group, Southern California Kaiser,
Permanente, Panorama City, California
National Immunization Program, Vaccine Safety and Development Activity, Centers
for Disease Control and Prevention, Atlanta, Georgia
Objective. To investigate trends over time in polio
extraimmunizationamong children in 4 large health maintenance
organizations andto study the association with recent changes in
polio immunizationpolicy.
Methods. Using 176 169 children who were born after 1994 andenrolled for their first 2 years of life, we assessed ratesand
trends of polio extraimmunization in the Vaccine SafetyDatalink
project. We used logistic regression to test the associationof
extraimmunization with different polio immunization schedulesand
with sociodemographic characteristics and used Poisson regressionto
test changes in rates over time.
Results. Overall, 10.5% were extraimmunized for poliovirus;
children on the all inactivated polio virus or sequential schedule
were one half as likely as those on the all oral polio virusschedule
to be extraimmunized by 2 years of age. There was asignificant
decrease in extraimmunization over time, with <5%of children born at
the end of 1997 being extraimmunized, comparedwith >15% at the
beginning of 1994.
Conclusions. Poliovirus extraimmunization rates have fallen
dramatically in association with the change-over to the all
inactivated polio virus schedule.
Key Words: extraimmunization polio vaccine
Abbreviations: OPV, oral polio virus IPV, inactivated
polio virus DTP, diphtheria and tetanus toxoids and whole-cell pertussis
DTaP, diphtheria and tetanus toxoids and acellular pertussis Hib,
Haemophilus influenzae type b HBV, hepatitis B virus MMR,
measles-mumps-rubella HMO, health maintenance organization GHC, Group Health
Cooperative of Puget Sound SCK, Southern California Kaiser Permanente Health
Care Program NCK, Northern California Kaiser Permanente Health Care Program
NWK, Kaiser Permanente Northwest
Received for publication Jun 3, 2002; accepted Sep 23, 2002.
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