Duration and density of natural pneumococcal colonisation in Malawian adults

Principal Investigator: Kondwani Jambo
Institution: Liverpool School of Tropical Medicine (LSTM); Malawi Liverpool Wellcome Trust Clinical Research Programme
Co-Investigators: Rob Heyderman, Neil French, Stephen Gordon, Thandie Mwalukomo, Todd Swarthout, Tinashe Nyazika

In Europe and North America, there has been a dramatic impact of pneumococcal conjugate vaccines (PCV) on vaccine serotype (VT) pneumococcal carriage and disease in both vaccinated (direct protection) and unvaccinated age groups (indirect protection). In high carriage prevalence and high disease burden settings such as sub-Saharan Africa, the ecology and epidemiology of pneumococcal carriage differs markedly from resource-rich settings. In Malawi, despite the successful rollout of the PCV13, the herd immunity benefits amongst high-risk adult populations are still not evident 6 years after introduction of the vaccine. The pneumococcal colonisation rates remain high in HIV-infected adults on ART (40%; 14% vaccine-type carriage). This suggests that HIV-infected individuals on ART represent an important yet under recognised potential pneumococcal reservoir for transmission. This may also explain the persistently increased risk of pneumococcal disease. In most endemic lower-middle income countries (LMIC), this potential reservoir of HIV-infected adults is likely to increase as life-expectancy increases due to the successful extensive roll out of ART and the introduction of the test & treat strategy.

The reasons behind the persistently high pneumococcal colonisation rates in HIV-infected adults on ART are still not well defined. Strengthening our understanding of pneumococcal carriage dynamics is crucial if  we are to reduce to impact of this expanding pneumococcal reservoir on disease and transmission. This work will inform vaccine scheduling and the design of alternative PCV regimens in this adult population.

The primary objective is to determine whether a longer duration and higher density of pneumococcal colonisation explain the persistently high point prevalence estimates of pneumococcal colonisation in otherwise healthy HIV-infected adults on ART compared to compared to HIV-uninfected adults

The secondary objective is to assess the utility of nasal wash versus pernasal swabs in measuring pneumococcal carriage density