Impact of the sequential poliovirus immunization schedule: a demonstration project

Immunogenicity and persistence from different 3-dose schedules of live and inactivated polio vaccines in Chinese infants

BACKGROUND

OPV is the only poliovirus vaccine used in the China EPI system, although IPV is available in the private market. We compared immunigencity and persistence among different schedules of IPV and OPV.

METHODS

536 Chinese infants were enrolled into 4 groups receiving different schedules administered at 2, 3, and 4 months of age: IPV-OPV-OPV, IPV-IPV-OPV, IPV-IPV-IPV, and OPV-OPV-OPV. The I-I-I group received an 18-month IPV booster dose. Blood samples were collected before the first dose, after the third dose, and at 18 months for all groups, and also after the booster dose for the I-I-I group. Polio neutralizing antibody titers were assessed, and seroprotection rates were calculated after primary immunization and at 18 months of age.

RESULTS

Before the first dose, GMTs of the 4 groups ranged from 2.96 to 6.89, and seroprotection rates ranged from 17.6% to 54.3%. After 3 doses, the GMT of the I-O-O and I-I-O groups ranged from 901.09 to 1,110.12, and the GMT of the I-I-I group range was 212.02 to 537.52, significantly lower than for the 2 sequential schedules (P<0.001). Seroprotection rates were 98.1% to 100%, with no significant differences among groups. At 18 months of age, the GMTs declined to a range of 527.00 to 683.44 in the I-O-O and I-I-O groups, and declined to 150.04 to 239.89 in the I-I-I group, significantly lower than for the other 3 groups (P<0.001).

CONCLUSIONS

The sequential schedules achieved high GMTs and seroprotection. The IPV-only schedule achieved high seroprotection but with lower GMTs. Sequential schedules are suitable for China. With the 2 sequential schedules, GMTs remained high at 18 months of age and were not inferior to the OPV-only schedule. Thus, with a sequential schedule, the booster dose could be given at 4 years of age, the same age as the current OPV booster dose.

Impact of multiple injections on immunization rates among vulnerable children

BACKGROUND

In 1997, the Advisory Committee on Immunization Practices (ACIP) recommended a switch from oral polio vaccine (OPV) to inactivated polio vaccine (IPV) for the first two infant doses. The ACIP also recommended use of diphtheria, tetanus, and acellular pertussis vaccine (DTaP) for infants. These recommendations resulted in two additional injections at the 2- and 4-month immunization visits. This study evaluates the implementation of new IPV and DTaP immunization recommendations and their impact on immunization coverage levels.

METHODS

Immunization coverage was assessed in public clinics in three urban areas before and after the recommendations. One pre- and three post-recommendation cohorts were followed to 12 months of age.

RESULTS

Almost all (> or = 88%) infants in the pre-recommendation cohort received OPV, DTP, and only one or two injections. Almost all (> or = 78%) infants in the post-recommendation cohorts received IPV, DTaP, and three or four injections. The percentage of infants in the post-recommendation cohorts up-to-date for immunizations at 12 months of age was slightly higher than those in the pre-recommendation cohort.

CONCLUSIONS

Providers rapidly switched from OPV and DTP to IPV and DTaP. Coverage at 12 months of age was higher among IPV/DTaP recipients than among OPV/DTP recipients. Provider and parent acceptance of four injections at a visit was high. The recent pneumococcal conjugate vaccine recommendations potentially add a fifth injection at 2 and 4 months of age. Acceptance or rejection of five injections by providers and parents needs early assessment.

Impact of the change to inactivated poliovirus vaccine on the immunization status of young children in the United States: a study from pediatric research in office settings and the National Medical Association

OBJECTIVE

To determine whether the change from an all oral poliovirus vaccine (OPV) schedule to an inactivated poliovirus vaccine (IPV)-containing schedule has adversely affected the immunization status of young children in the United States.

METHODS

Immunization data were abstracted from the medical records of children 8 to 35 months old seen consecutively for any reason in the offices of practicing pediatricians who are members of the Pediatric Research in Office Settings network of the American Academy of Pediatrics or the National Medical Association. Data on up to 120 eligible children were collected in each practice between March 1998 and January 2000. Patients were classified as fully immunized at 8 months old if they had received 3 diphtheria-tetanus-pertussis, 2 Haemophilus influenzae type b, 2 hepatitis B, and 2 poliovirus vaccines. Study children who were >/=12 months of age at the time that data were collected were categorized as being fully immunized at 12 months if they had received the same vaccines before their first birthday. To assess the effect of type of poliovirus vaccines on these outcomes, study patients were classified as being in an IPV or OPV group based on the initial type of vaccine received. Logistic regression was used to calculate the odds ratios (ORs) and 95% confidence intervals (CIs) for IPV as a predictor of being fully immunized at 8 and 12 months of age, after adjusting for race/ethnicity of the patient, maternal education level, year of birth, and method of payment for vaccines. In addition, the effect of clustering of children within practices was accounted for by the use of generalized estimation equation techniques.

RESULTS

Data were analyzed on 13 520 children from 177 practices in 42 states; 79.4% of patients were fully immunized at 8 months of age, and 88.7% of those eligible were fully immunized at 12 months of age. A total of 6910 patients (51.1%) were classified as OPV recipients, wheras 5282 (39.1%) received IPV. In addition, 1328 children (9.8%) were documented as having received poliovirus vaccine, but the particular type could not be determined. Compared with OPV recipients and after controlling for the confounding variables and the effect of clustering within practices, children in the IPV group were as likely as were OPV recipients to be fully immunized at 8 months of age (OR: 1.04; 95% CI: 0.88,1.23). At 12 months of age, the OR for IPV as a predictor of being fully immunized was 1.08 (95% CI: 0.90,1.30). When compared with OPV recipients, adjusted ORs for children in the undetermined poliovirus vaccine type group being fully immunized at 8 and 12 months of age were 0.84 (95% CI: 0.68,1.04) and 0.84 (95% CI: 0.67,1.07), respectively.

CONCLUSIONS

The results of this national study indicate that the implementation of an IPV-containing poliovirus vaccine schedule has not had an adverse effect on the immunization status of young children who were vaccinated in the offices of practicing pediatricians.

Impact of the change in polio vaccination schedule on immunization coverage rates: a study in two large health maintenance organizations

OBJECTIVE

In January 1997, one of the most significant changes to United States vaccine policy occurred when polio immunization guidelines changed to recommend a schedule containing inactivated polio vaccine (IPV). There were concerns that parent or physician reluctance to accept IPV into the routine childhood immunization schedule would lead to lowered coverage. We determined whether adoption of an IPV schedule had a negative impact on immunization coverage.

DESIGN

A cohort study of 2 large health maintenance organizations (HMOs), Group Health Cooperative and Kaiser Permanente Northern California, was conducted. For analysis at 12 months of age, children who were born between October 1, 1996, and December 31, 1997, and were commercially insured and covered by Medicaid were continuously enrolled; for analysis at 24 months of age, children who were born between October 1, 1996, and June 30, 1997, and were commercially insured and covered by Medicaid were continuously enrolled. The 3 measures of immunization status at 12 and 24 months of age were up-to-date status, cumulative time spent up-to-date, and the number of missed opportunity visits.

RESULTS

At both HMOs, children who received IPV were as likely to be up to date at 12 months as were children who received oral poliovirus vaccine (OPV), whereas at Group Health, children who received IPV were slightly more likely to be up to date at 24 months (relative risk: 1.12; 95% confidence interval [CI]: 1.05, 1.19). These findings were consistent for children who were covered by Medicaid. At Kaiser Permanente, children who received IPV spent ~3 fewer days up to date in the first year of life, but this difference did not persist at 2 years of age. At Group Health, children who received IPV were no different from those who received OPV in terms of days spent up to date by 1 or 2 years of age. At Group Health, children who received IPV were less likely to have a missed opportunity by 12 months old (odds ratio [OR] 0.46; 95% CI: 0.31, 0.70), but this finding did not persist at 24 months of age. At Kaiser Permanente, children who received IPV were more likely to have a missed opportunity by 12 months (OR 2.06; 95% CI: 1.84, 2.30), and 24 months of age (OR 1.50; 95% CI: 1.36, 1.67).

CONCLUSIONS

The changeover from an all-OPV schedule to one containing IPV had little if any negative impact on vaccine coverage. Use of IPV was associated with a small increase in the likelihood of being up to date at 2 years of age at one of the HMOs and conversely was associated with a small increase in the likelihood of having a missed-opportunity visit in the other HMO.polio, poliomyelitis, vaccination, immunization coverage.

Poliovirus vaccines. Progress toward global poliomyelitis eradication and changing routine immunization recommendations in the United States

Poliomyelitis prevention in the United States has relied virtually exclusively on OPV during the past 30 years. Starting in 1997, a major change in the poliomyelitis vaccination policy occurred, facilitated by substantial progress toward worldwide poliomyelitis eradication. A sequential schedule of IPV followed by OPV became the preferred means to prevent poliomyelitis, although an all-OPV and an all-IPV schedule were considered acceptable alternatives. In 1999, two doses of IPV were recommended to start the primary series, followed by two doses of either poliovirus vaccine. As of January 2000, an all-IPV schedule is currently being implemented in the United States for routine childhood vaccination. Several unusual features are associated with the major public health policy change from an all-OPV to a sequential schedule, including (1) the process of involving a neutral party (i.e., the IOM); (2) the perceived concerns expressed before the change in policy with regard to provider and parent compliance, which could affect the hard-earned gains in raising immunization coverage rates; (3) the ethical issues surrounding the change (e.g., societal versus individual protection) and the influence that a single case of VAPP may have on national policy; (4) the relative lack of importance of cost-effectiveness data; and (5) the weight of progress in the global polio eradication initiative spurring the change in the United States and, increasingly, in other industrialized countries. The IOM assisted in the evaluation of the national poliomyelitis vaccination policy in 1977 and again in 1988. The 1988 review recommended that a sequential IPV-OPV schedule be considered at such time that a combination vaccine becomes available. Also, the IOM raised several important questions. Extensive research to address the questions raised by the IOM had been conducted so that, in 1996, more data were available for the decision-making process. The primary reasons for the change in vaccination policy were (1) the continued occurrence of VAPP in the absence of indigenously acquired wildtype poliovirus-associated paralytic disease, (2) the reduced risk for importation and spread of wild-type poliovirus caused by the progress of the global polio eradication initiative, (3) evidence from vaccine trials that combined IPV-OPV schedules are safe and immunogenic, and (4) maintenance of high levels of population immunity to poliovirus. The global effect of a national change in poliomyelitis vaccination policy was also considered in this policy-making process. Some members of the public health and medical communities raised objections that an increased reliance on IPV in the United States could lead other countries, especially developing countries, to inappropriately abandon OPV and increase reliance on IPV for routine vaccination. Experience from the global smallpox eradication campaign indicated that this scenario was unlikely. The United States ceased vaccinating against smallpox in 1971, 6 years before smallpox was eliminated from the world, without jeopardizing the global smallpox campaign. Subsequently, the effect on the global eradication initiative has been negligible. This article illustrates the potential discrepancy between expressed theoretic concerns about the number of injections and the actual practice once vaccination policy recommendations become the standard of care and that appropriate training and education can overcome these initial concerns. The authors found that compliance with the recommended use of IPV for the first and second doses as part of the sequential schedule was high, independent of socioeconomic status and ethnicity. The need for additional injections did not present a barrier to completion of the recommended childhood immunization schedule. (ABSTRACT TRUNCATED)