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Combination vaccines improve vaccine uptake and open the infant immunization space for additional vaccines. Hexavalent vaccines have been marketed since 2000. Infanrix hexa (combined diphtheria-tetanus-acellular pertussis-hepatitis B-inactivated poliovirus-Haemophilus influenzae type b conjugate vaccine, DTPa-HBV-IPV/Hib, GSK) is longest on the market, providing 16 years post-marketing experience. Each DTPa-HBV-IPV/Hib vaccine component is licensed alone and/or in smaller combination vaccines. Programmatic considerations sometimes require an interchange between vaccines due to unavailability, program change or mixed schedules (when the number of required antigens differs across scheduled primary vaccination visits).Immunogenicity and safety data from 11 GSK-sponsored clinical trials support the interchangeability of DTPa-HBV-IPV/Hib within the same vaccines family, and use of DTPa-HBV-IPV/Hib in mixed primary vaccination schedules.Data show acceptability of interchange of DTPa-HBV-IPV/Hib with other products within the same vaccines family and its use in mixed immunization schedules. This aligns with WHO recommendations that vaccines of the same family from the same manufacturer be used to complete the infant vaccination schedule. Interchangeability and suitability for use in mixed schedules is of interest for policy-makers/providers in the framework of vaccination recommendations as it provides flexibility. Given the complexity of larger combination vaccines, interchangeability or sequential use needs careful assessment.

Universal infant vaccination with the 7-valent pneumococcal conjugate vaccine (PCV7) has nearly eliminated PCV7-serotype invasive pneumococcal disease (IPD) in young U.S. children, but has been accompanied by increases in the incidence of serotype 19A IPD. Because antibiotic-non-susceptible 19A has increased more than antibiotic-susceptible 19A, antibiotic selection pressure could be contributing to this trend. We developed a dynamic compartmental transmission model of pneumococcus to better understand the causes of this rise and to estimate the impact of vaccines or changes in antibiotic use on future IPD incidence in the U.S. in