In January 1997, the Advisory Committee on Immunization Practices (ACIP) recommended adoption of a sequential inactivated poliovirus vaccine (IPV)-oral poliovirus vaccine (OPV) vaccination schedule.1 The schedule of injections of IPV at 2 months and 4 months of age, followed by OPV at 12-18 months and again at 4-6 years was intended to minimize the risk for vaccine-associated paralytic poliomyelitis (VAPP) while maintaining population immunity to the potential introduction of wild-type poliovirus. To determine whether this change may result in reduced or delayed vaccination coverage because parents or physicians might be reluctant to administer multiple injections at a single visit,2 CDC investigated the impact of the change to a sequential IPV-OPV vaccination schedule at two large West coast health maintenance organizations (HMOs). This report summarizes the results of the investigation and indicates that changing to an initial two doses of IPV was not associated with decreases in vaccination coverage levels of routinely recommended vaccinations.
This study focused on children enrolled at Group Health Cooperative of Puget Sound (GHC), a Seattle-based HMO with approximately 530,000 members, and Kaiser Permanente of Northern California (KPNC), an Oakland-based HMO with approximately 2.8 million members. Both sites have automated vaccination tracking systems3 that allow for assessment of vaccination coverage by region, clinic, and individual patient. Beginning in April 1997, GHC adopted the ACIP guidelines for the sequential IPV schedule as an option for physicians and families. Within KPNC, each of its 17 medical centers made a local decision about whether and when to adopt the IPV schedule. Children in the study were born during October 1, 1996-June 30, 1997; resided in King, Pierce, Thurston, and Kitsap counties, Washington, and all counties of the KPNC region; had been continuously enrolled during the first 12 months of life; and had received at least one polio vaccination (N=1745 GHC and 15,707 KPNC enrollees). Up-to-date status, defined as receipt of two polio vaccinations, three diphtheria and tetanus toxoids and pertussis/acellular pertussis (DTP/DTaP) vaccinations, and two Haemophilus influenzae type b and two hepatitis B vaccinations administered after age 3 weeks, was measured at age 12 months.
The percentage of GHC children who received their first polio vaccine as IPV increased from 18% during the fourth quarter of 1996, to 19% in the first, 34% in the second, and 82% in the third quarter of 1997. Among GHC clinics that had at least 20 children in the evaluation, the percentage of children who received IPV during the third quarter of 1997 ranged from 81% to 98%. In comparison, at KPNC, the percentages by quarter were 10%, 15%, 24%, and 36%, respectively; among KPNC clinics that had at least 20 children in the evaluation, the percentage of children who received IPV during the fourth quarter ranged from 6% to 98%. Among GHC children who received IPV as their first polio vaccination, vaccination up-to-date status by age 12 months for routinely recommended vaccines was 82%, 83%, and 82% in the first three quarters following implementation, and among those receiving OPV, vaccination up-to-date status was 82%, 81%, and 79%, respectively. At KPNC, the quarterly up-to-date percentages were 90%, 89%, and 91% for children receiving IPV, and 92%, 90%, and 91% for children receiving OPV.
After adjusting for sex, trends over time, Medicaid status, and primary clinic, GHC children receiving IPV as their first polio vaccination were as likely to be up-to-date at age 12 months as children receiving OPV (risk ratio [RR]=1.1; 95% confidence interval [CI]=1.0-1.3). KPNC children receiving IPV as their first polio vaccination also were as likely as those receiving OPV to be up-to-date (RR=1.0; 95% CI=0.9-1.0). At GHC, children enrolled in Medicaid had lower coverage levels at age 12 months (71% up-to-date among Medicaid enrollees compared with 83% among nonenrollees); KPNC Medicaid enrollees and non-Medicaid enrollees had similar up-to-date status (90% compared with 91%, respectively). Among GHC Medicaid enrollees, vaccination with IPV was not significantly associated with a decreased up-to-date status (68% at age 12 months among IPV recipients compared with 73% at age 12 months among OPV recipients). At KPNC, Medicaid enrollees receiving IPV were as likely to be up-to-date as those receiving OPV (91% compared with 90%, respectively).
RL Davis, LK Mell, A Zavitkovsky, RS Thompson, Immunization Studies Program, Center for Health Studies, Group Health Cooperative, Seattle, Washington. TA Lieu, Div of Research, AM Capra, C Quesenberry, SB Black, HR Shinefield, Kaiser Permanente of Northern California, Oakland, California. Child Vaccine Preventable Diseases Br, Epidemiology and Surveillance Div and Health Svcs Research and Evaluation Br, Immunization Svcs Div, National Immunization Program, CDC.
The findings in this report indicate that use of IPV for the initial polio vaccine doses in these two West coast HMOs was not associated with decreases in vaccination coverage levels. These findings are consistent with evaluations conducted in other settings, including clinics serving children from low-income families.4- 6
An important ancillary finding from the study was that the sequential polio vaccination schedule was implemented to a much greater degree in the HMO that used a more centralized decision making process than in the HMO that relied on local decision making (82% compared with 36%, respectively, for the percentage of children who received IPV for their initial polio vaccination). In the United States, use of IPV increased from 6% of all polio vaccine doses distributed in 1996 to 29% in 1997 (CDC, unpublished data, 1998).
Despite the increased use of IPV, four cases of VAPP have occurred in the United States since January 1997. All cases were associated with receipt of the first or second dose of OPV vaccine in an all OPV schedule; three cases were in OPV recipients, and one case was in an adult contact of an OPV recipient.
To further reduce the incidence of VAPP by decreasing reliance on OPV for the initial doses of poliovirus vaccine, in October 1998, ACIP changed the routine childhood polio vaccination schedule. Use of OPV is no longer recommended for the first two doses except in special circumstances (e.g., a child whose parents do not accept the recommended number of injections or who will be traveling to areas with endemic polio). OPV remains the vaccine of choice for mass vaccination campaigns to control outbreaks associated with wild poliovirus.
Impact of the Sequential IPV/OPV Schedule on Vaccination Coverage Levels—United States, 1997. JAMA. 1999;281(3):223-224. doi:10.1001/jama.281.3.223