Prevalence of Nasopharyngeal Pneumococcal Carriage and Otitis Media Among Cameroonian Children Under-five Years Old in The Era of 13-valent Pneumococcal Conjugate Vaccine: Baseline all-cause under-five mortality data and vaccine impact on otitis media

John Njuma Libwea

Research output: Book/ReportDoctoral thesisCollection of Articles


Streptococcus pneumoniae has more than ninety serotypes and continue to be a major cause of childhood illnesses and deaths worldwide. Treating affected children and preventing the spread of infection is a critical public health priority especially in developing countries including Cameroon. The 13-valent pneumococcal conjugate vaccine (PCV13) was introduced to Cameroon's Expanded Programme on Immunization (EPI) in July 2011, through funding from the Global vaccine alliance initiative (GAVI, the Vaccine Alliance). PCV13 is administered to infants using the accelerated primary dose series of three doses at six, ten and fourteen weeks of age. PCV13 vaccination programme targets the prevention of paediatric invasive pneumococcal diseases and infections of the middle ear resulting from the pneumococcus. In the absence of GAVI funding, sustaining PCV13 immunization in Cameroon, as in most low-income economies, would be practically impossible. It will rely heavily on convincing policymakers of the PCV’s effectiveness in reducing the burden of disease associated with pneumococcal infections as well as overall under-five morbidity and mortality.

However, studies evaluating the effectiveness of the PCV-13 against both mucosal and invasive pneumococcal diseases as well as nasopharyngeal carriage in the country are lacking. The purpose of this research project was to estimate the baseline proportion of pneumococcal associated deaths, prevalence of otitis media, and nasopharyngeal carriage of Streptococcus pneumoniae among children under the age of five who were vaccinated with PCV13 versus those who were not vaccinated during the PCV13 era.

This dissertation consists of four original studies. A retrospective cohort study design was used to examine existing hospital data on the major causes of under-five mortality recorded at the infectious disease surveillance sites (hospitals) in Yaoundé, between January 2006 and December 2012 (Study I). In order to examine the prevalence of otitis media and nasopharyngeal carriage in the era of PCV13, two rounds of surveillance studies were conducted in which tympanometry data and nasopharyngeal swabs were collected from randomly selected 24 to 36 months old children living in and around Yaoundé, in 2013 and 2015, respectively. Children born between June 2010 and June 2011 (baseline data) and between June 2012 and June 2013 (comparison data), were targeted (Studies II, III and IV).

The findings from Study I (N=817) provided country-specific evidence that approximately 29% of under-five deaths between January 2006 – December 2012 were due to pneumococcal infections (including pneumonia, meningitis and sepsis). Additionally, more than 70% of children in this setting die before their second birthdays. In Study II (N=877), overall carriage and residual vaccine-type pneumococci prevalence were 62% and 18%, respectively. Furthermore, eleven of the thirteen vaccine-serotypes were still in circulation. However, the 18% residual vaccine-type pneumococci obtained in Cameroon four years after PCV13 introduction were not very different from those reported in The Gambia (13%), except that, only three vaccine-type pneumococci were identified four years after infant vaccination programme. The results of the otitis media studies were surprising. Two years after PCV13 introduction in 2013 (Study III, N=433), 9.7% of PCV13-unvaccinated children had otitis media (OM). Four years after PCV13 implementation (Study IV, N=413), 16.7% of PCV13-vaccinated children had OM. This shows an unexpectedly higher OM prevalence among the PCV13-vaccinated group compared to the PCV13-unvaccinated. Additionally, PCV13 effectiveness estimate against OM prevalence was negative 72%, four years after PCV13 infant vaccination. However, multivariate analyses did not show any statistically significant evidence that PCV13-vaccinated children in 2015 were associated with higher odds of OM compared to PCV13-unvaccinated children in 2013. Furthermore, the attributable proportion estimates which depicts the public health impact of PCV13 against OM infection was 42%; suggesting that the remainder (58%) of OM infections in the PCV13-vaccinated cohort would have still occurred even without PCV13 vaccination. However, study participants were drawn from same population overtime, and the results may be attributed to several factors including: the predominance of other pathogens and/or non-PCV13-type pneumococci as disease causing microbes or early vaccine waning effects or residual confounding. Furthermore, immunity due to natural exposure could as well be a contributing factor.

In conclusion, these findings support the need for continuous surveillance to determine the possible long-term effects of the PCV13 implementation programme in Cameroon on nasopharyngeal carriage, pneumococcal disease and pneumococcal-associated under-five mortality.

I am of the opinion that in addition to these findings, the evidence and gaps on the broader public health impact of the PCV13 implementation discussed in this thesis will support Cameroon government’s policies to prioritize the continuation of PCV13 programme in the absence of GAVI funding.
Original languageEnglish
Place of PublicationTampere
ISBN (Electronic)978-952-03-2523-7
Publication statusPublished - 2022
Publication typeG5 Doctoral dissertation (articles)

Publication series

NameTampere University Dissertations - Tampereen yliopiston väitöskirjat
ISSN (Print)2489-9860
ISSN (Electronic)2490-0028


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