What is the best way to use conjugate vaccines?

The present review discusses recent advances, challenges and opportunities for the best use of conjugate vaccines now and in the future.

Direct protection in young children may be short-lived and programme effectiveness may depend heavily on indirect protection (herd immunity). Pneumococcal carriage serotype replacement has been widely reported following vaccine implementation. Use of pneumococcal conjugate vaccines is being trialled in the elderly. Vaccination in west Africa against Neisseria meningitidis serogroup A (Men A), a new monovalent conjugate vaccine, was commenced in December 2010. New conjugate vaccines against, for example, Salmonella typhi and Streptococcus agalactiae, are being developed and tested in clinical trials.

Conjugate vaccines have been extensively used to immunize children, resulting in significant decreases in childhood morbidity and mortality. Since their introduction, evidence has grown that protection against disease is due to both direct and indirect protection (herd immunity). The optimization of priming and booster dose regimens in existing paediatric vaccination programmes, aiming for maximal and sustained direct and indirect protection using as few doses per child as possible, may broaden conjugate vaccine impact and augment cost-effectiveness in the future. This may be particularly important in strategies for wider global use of conjugate vaccines in children, as well as use in adults and the elderly. Challenges such as pneumococcal serotype replacement make ongoing surveillance of carriage and invasive disease crucial and will have implications for conjugate reformulation and the development of alternative vaccines. New conjugate vaccines for other pathogens currently in clinical trials have the potential to reduce invasive bacterial disease further, particularly in resource-poor settings.