Poliomyelitis prevention in the United States: new recommendations for routine childhood vaccination place greater reliance on inactivated poliovirus vaccine

Genomic analysis of vaccine-derived poliovirus strains in stool specimens by combination of full-length PCR and oligonucleotide microarray hybridization

Sabin strains of poliovirus used in the manufacture of oral poliovirus vaccine (OPV) are prone to genetic variations that occur during growth in cell cultures and the organisms of vaccine recipients. Such derivative viruses often have increased neurovirulence and transmissibility, and in some cases they can reestablish chains of transmission in human populations. Monitoring for vaccine-derived polioviruses is an important part of the worldwide campaign to eradicate poliomyelitis. Analysis of vaccine-derived polioviruses requires, as a first step, their isolation in cell cultures, which takes significant time and may yield viral stocks that are not fully representative of the strains present in the original sample. Here we demonstrate that full-length viral cDNA can be PCR amplified directly from stool samples and immediately subjected to genomic analysis by oligonucleotide microarray hybridization and nucleotide sequencing. Most fecal samples from healthy children who received OPV were found to contain variants of Sabin vaccine viruses. Sequence changes in the 5' untranslated region were common, as were changes in the VP1-coding region, including changes in a major antigenic site. Analysis of stool samples taken from cases of acute flaccid paralysis revealed the presence of mixtures of recombinant polioviruses, in addition to the emergence of new sequence variants. Avoiding the need for cell culture isolation dramatically shortened the time needed for identification and analysis of vaccine-derived polioviruses and could be useful for preliminary screening of clinical samples. The amplified full-length viral cDNA can be archived and used to recover live virus for further virological studies.

Immunizations for international travel

Many infections encountered by international travelers can be prevented by adherence to personal protective measures and appropriate vaccinations. This review outlined the incidence and importance of the major vaccine-preventable infectious diseases encountered by U.S. travelers, as well as the indications, contraindications, and side effects of available vaccines. Official proof of yellow fever vaccine often is required for entry into some countries. Based on endemic or epidemic infections at destinations, planned activities, and age and medical history of international travelers, other vaccines may be recommended. Many clinicians will be familiar with some of the infections and vaccines that may be used in travelers; other vaccines may be encountered infrequently and associated with significant risk of adverse effects. Since vaccines do not provide complete protection and some travel-related infections do not have vaccines available yet (e.g., malaria and dengue fever), physicians need to be vigilant concerning febrile illness in returning travelers.

Parental attitudes toward multiple poliovirus injections following a provider recommendation

OBJECTIVES

Changes to the polio vaccination schedule, first to a sequential inactivated poliovirus/oral poliovirus (IPV/OPV) schedule in 1996 and most recently to an all-IPV schedule, require infants to receive additional injections. Some surveys show parental hesitation concerning extra injections, whereas others show that parents prefer multiple simultaneous injections over extra immunization visits. This study describes parental behavior and attitudes about the poliovirus vaccine recommendations and additional injections at the 2- and 4-month immunization visits.

METHODS

Beginning July 1, 1996, providers in eight public health clinics in Cobb and Douglas Counties, Georgia, informed parents of polio vaccination options and recommended the IPV/OPV sequential schedule. A cross-sectional clinic exit survey was conducted from July 15, 1996, to January 31, 1997, with parents whose infants (younger than 6 months) were eligible for a first poliovirus vaccination.

RESULTS

Of approximately 405 eligible infants, parents of 293 infants were approached for an interview, and 227 agreed to participate. Of those 227 participants, 210 (92%) parents chose IPV for their infant and 17 (8%) chose OPV. Of greatest concern to most parents was vaccine-associated paralytic polio (VAPP) (155, or 68.3%); the next greatest concern was an extra injection (22, or 9.7%). These parental concerns were unrelated to the number of injections the infant actually received.

CONCLUSIONS

After receiving information on polio vaccination options and a provider recommendation, parents overwhelmingly chose IPV over OPV. Concern about VAPP was more common than objection to an extra injection. The additional injection that results from using IPV for an infant's first poliovirus vaccination appears to be acceptable to most parents.

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.

Parental opinions regarding poliomyelitis immunizations

The successful eradication of poliomyelitis in the United States has primarily been due to the use of oral poliovirus vaccine (OPV). However, because of the risk of vaccine-associated paralytic poliomyelitis with OPV, the use of inactivated poliovirus vaccine (IPV) has become the accepted option. We performed a cross-sectional survey of parents of children less than 18 months of age to determine parental preference regarding poliomyelitis vaccine options. Parents were asked questions about their knowledge regarding poliomyelitis and available vaccines. Parents were also given information about the risks and benefits of the 3 immunization options (all OPV, all IPV, and sequential IPV/OPV) and then asked to choose among the 3 schedules. We distributed 146 questionnaires, with an 88% response rate. Parents were, on average, 22 years old and had 12 years of education. Fifty-eight percent of parents thought that decisions regarding vaccine choices should be made by the physician and caregiver together. However, when given the choice, 41 % could not decide among the different vaccine options. One quarter (25%) chose the all OPV, 13% the all IPV, and 21% the sequential IPV/OPV schedule. Older parents were more likely to choose the all IPV schedule (p=0.042). There was no correlation with the parental level of education. More studies are required to determine if further education will empower urban parents to be more active participants in the medical decision process.

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)

Impact of the sequential poliovirus immunization schedule: a demonstration project

OBJECTIVE

Researchers for this project evaluated compliance with the sequential poliovirus immunization schedule that uses inactivated poliovirus vaccine (IPV) for the first 2 doses of the polio immunization series, and assessed immunization coverage rates before and after implementation of this schedule at 6 public health clinics serving 1 county in Georgia.

DESIGN

Immunization histories for 3 birth cohorts of infants were compared: (1) the baseline cohort, born January 1 through June 30, 1995; (2) the evaluation cohort, born January 1 through June 30, 1997, after implementation of the schedule change; and (3) the dose-3 cohort, born August 1 through November 30, 1996 (i.e., old enough to be eligible for a third dose of poliovirus vaccine following implementation of the sequential schedule).

RESULTS

Following implementation of the new poliovirus immunization recommendations, 94% (534 of 567) of infants who received their first dose of poliovirus vaccine by age 3 months received IPV. Among these infants, 99.6% (532 of 534) were also up to date (UTD) for first doses of diphtheria and tetanus toxoids and acellular pertussis vaccine (DTP1/DTaP1), 99.6% (532 of 534) were UTD for first doses of hemophilus influenza type b (Hib 1), and 98.6% (527 of 534) had received at least one dose of Hepatitis B. Among infants visiting the clinics for their first or second dose of poliovirus vaccine, DTaP/DTP, and/or Hib, 76% received 3 or 4 simultaneous injections. In the dose-3 cohort, 78% (145 of 185) of infants who received a third dose of poliovirus vaccine had received 2 doses of IPV and 1 dose of oral poliovirus vaccine.

CONCLUSIONS

Compliance with the recommended use of IPV for the first 2 poliovirus immunization doses as part of the sequential schedule was very high in this low-income and ethnically diverse population. Furthermore, the need for additional injections did not impede the delivery of recommended childhood immunizations.