Vaccines

Vaccine research has been at the centre of research activities in Karonga since the start of the programme. The evaluation of BCG and Leprosy vaccines has left a continued legacy of vaccine and vaccine related research in many of the topic areas. Most recently pneumococcal disease and vaccines have become a central vaccine theme. Since 2007 there has been a series of interlinked studies to measure the burden of respiratory infections in adults and children, understand the role HIV plays in driving pneumococcal disease, studies of the transmission of pneumococcus within the community and most recently an evaluation of the impact of the introduction of 13-valent pneumococcal conjugate vaccine to the infant vaccine schedule in Malawi.

Key findings from this work have highlighted the importance of older siblings as reservoirs and transmitters of the pneumococcus. HIV-infected adults carry pneumococcus more frequently and longer than HIV-uninfected adults and show a failure to reconstitute their mucosal immune responses post effective ART and persist in carrying at high frequency. This in part explains their continued elevated susceptibility to this serious infection, but also their ability to act as a potential reservoir of infection. Despite this, transmission of pneumococcus between mother and newborn infants is relatively unaffected by HIV. Since the introduction of pneumococcal vaccine we are starting to see a decline in vaccine type pneumococcal carriage, but the evolution of this process is at a much slower rate than expected from other settings and raises issues about the most appropriate vaccine schedule for use in this setting and the role of vaccinating HIV-infected adults to speed up the development of herd immunity. Under 5 disease surveillance has identified lower respiratory tract infections as the principal cause of health service utilisation. Post PCV13 introduction we are seeing a reduction in severe and very severe pneumonia cases consistent with a vaccine effect.

Current studies (2012-2016)

Going forward we will be continuing to monitor the carriage and transmission of pneumococcus in the post PCV13 period, collecting both empirical data and using models to predict the impact of alternative vaccine schedules. Using the DSS we will estimate the impact of PCV13 on infant and under 5 mortality. Pneumococci collected from the longitudinal surveys in Chilumba have been sequenced and we are studying the impact of PCV13 introduction on microbial ecology at the genetic level and seeking signals that might indicate emergence of new pathogenic strains.

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