Doctoral Defence of John Njuma Libwea on Friday August 26th

Pneumococcal diseases are estimated to be the leading global cause of infections and death in under-five-year-old children. Furthermore, ear infections can cause hearing loss and even deafness, jeopardising the affected person’s ability to communicate in social environments. The development of pneumococcal conjugate vaccines (PCVs) remains a major advancement in global child health.

In Cameroon, the 13-valent PCV (PCV13) vaccine was added to the national childhood immunisation programme to reduce the burden of illness and death of under-five-year-olds in July 2011. This thesis explores the changing trends in the global epidemiology of vaccine and non-vaccine serotypes following the implementation of the PCV13 programme in Cameroon. The findings give decision-makers and other national and international partners information about the societal needs that vaccination programmes are expected to address.

There were three main research questions. Firstly, what was the share of mortalities in under-five-olds caused by pneumococcal diseases prior to the implementation of the PCV13 programme in Cameroon? Secondly, what was the prevalence of ear infections among 2-3-year-olds, who had been vaccinated with PCV13, compared to children who had not been immunized? Thirdly, what was the prevalence of nasopharyngeal pneumococcal carriage among the PCV13-unimmunized and PCV13-immunized children aged 2–3 years after the introduction of PCV-13.

The study found that pneumococcal infections (including pneumonia, sepsis, and meningitis) accounted for more than 29 % of the deaths of under-five-year-olds during the studied period. The results also showed that, in 2015, PCV13-vaccinated children had a 17 % prevalence of ear disease compared to 10 % among the PCV13-unvaccinated children. This finding could be explained by the predominance of other microbes and non-PCV13-type pneumococci as disease-causing microbes among the PCV13-vaccinated children, or natural immunity could also be implicated.

The results also revealed that four years after the PCV13 infant vaccination, the carriage prevalence of residual vaccine-type pneumococci was 18 %. In 2015, eleven of the 13 vaccine serotypes were also isolated in carriage among the vaccinated children, suggesting that the 18 % residual vaccine-type carriage prevalence may be contributing to the high disease burden of, for example, otitis media i.e., middle-ear infections, but the lack of data on the microbial aetiology of OM prevents confirming the findings.

Further research is needed to assess the findings and potential causes, as well as to monitor the long-term impact of the PCV13 programme implementation on the epidemiology of pneumococcal diseases including ear disease in African settings during and beyond the COVID-19 pandemic. The scientific documentation of the impact of the vaccine programme is highly important for the pursuit of better child health globally. This is especially relevant for supporting the continuation of the vaccination programmes with public funding if no private funding is available.

The doctoral dissertation of MHS John Njuma Libwea in the field of Epidemiology and Public Health titled Prevalence of nasopharyngeal pneumococcal carriage and otitis media among Cameroonian children under-five years old in the era of the 13-valent pneumococcal conjugate vaccine: Baseline all-cause under-five mortality data and vaccine impact on otitis media” will be publicly examined in the Faculty of Social Sciences at Tampere University at 12:00 on Friday 26 August 2022 at Arvo building, Arvo Ylpon katu 34, Tampere, Finland. The Opponent will be Docent Tuula Pelkonen from the University of Helsinki, Finland. The Custos will be Professor of Epidemiology, Pekka Nuorti of the Tampere University, Faculty of Social Sciences.

The dissertation can be followed remotely via remote connection (Panopto).

The dissertation is available online at the