Combination vaccines and immunization visits

Vaccines administered simultaneously: directions for new combination vaccines based on an historical review of the literature

OBJECTIVES

The recognized benefits of administering vaccines simultaneously has encouraged vaccine producers to develop combination vaccines. If contemporary research and development can realize vaccines that achieve the current standards for safety, immunogenicity, and efficacy, other specific vaccine associations may also merit reconsideration as combination vaccines.

METHODS

An historical review of the vaccine association literature reveals two important themes: first, the programs of mass vaccination, in particular, the eradication of smallpox, sessions where multiple vaccines (other than the smallpox vaccine) were given concurrently, and the Expanded Programme on Immunization (EPI); and, second, the domain of travel vaccines, including travellers to a disease-endemic country (such as migrants, tourists, military personnel, or expatriates) and WHO requirements for international travellers.

RESULTS/CONCLUSIONS

Based on this historical review, combination vaccines worth reconsideration could fill epidemiologic niches in the EPI with, for instance, a measles--yellow fever, a measles--Japanese encephalitis or a pertussis-based paediatric combination rabies vaccine. Furthermore, other combinations could broaden protection against the pathogens responsible for meningitis, pneumonia, or enteric diseases. Nevertheless, complex issues such as necessity, feasibility, or affordability will ultimately determine if any one of these becomes a combination vaccine.

The hidden costs of infant vaccination

Combination vaccines to minimize injections required for infant vaccination, and new vaccines with improved safety profiles, will pose increasingly complex choices for vaccine purchasers in the future. How much of a premium to pay for such vaccines might be determined by taking into account (1) the psychological burden of multiple injections during a single clinic visit, and the costs of any additional visits to minimize these, and (2) the medical, work-loss, and incidental costs of common vaccine-associated symptoms. This cross-sectional survey included randomly-selected parents of 1-8-month-old infants who received vaccines in a Northern California health maintenance organization (HMO) in 1997. Interviewers called parents 14 days after the infant's vaccination to administer a 10-minute closed-ended interview in English or Spanish. Parents were asked about infant symptoms after vaccination, their preferences regarding multiple injections and their (theoretical) willingness to pay to reduce the number of injections their infant would receive, or to avoid the adverse symptoms experienced. Among 1769 eligible infants, interviews were completed with parents of 1657 (93%). The psychological cost of multiple injections was estimated by the willingness of parents to pay a median of $25 to reduce injections from 4 to 3, $25 from 3 to 2, and $50 from 2 to 1. Vaccine-associated symptoms caused mean costs of $42 in medical utilization and $192 in work-loss among the families who experienced those events (Ns=62 and 35, respectively). When averaged among all 1657 study infants, vaccine-associated symptoms after the index vaccination visit resulted in $2.91 in medical utilization, $4.05 in work-loss, and $0.74 in direct nonmedical costs, yielding total financial costs of $7.70. Parents of infants who had vaccine-associated symptoms said they would have paid a median of $50 to avoid these symptoms. Fever and fussiness were associated in logistic regression analysis with a two-fold increase in the odds of medical utilization, and fever with more than a three-fold increase in work loss. We conclude that multiple injections during a single clinic visit entail psychological costs. The psychological costs of vaccine-associated symptoms, as measured by willingness-to-pay methods, are higher than those resulting from multiple injections. The financial costs of medical utilization and work-loss resulting from common vaccine-associated symptoms are non-negligible and should be incorporated in economic analyses.

New combination vaccines

Physicians can achieve full vaccination at each of the recommended visits by administering three or four injections, but for infants, four injections seem to be a maximum in light of the size of the infant thigh, which is the preferred injection site. Thus, physicians must make room for all of the new vaccines on the horizon. To accomplish that task, combinations will be necessary. Progress toward that goal is occurring.