ABSTRACT
Pneumococcal diseases are responsible for killing at least one million children under the age of five every year: over 70% of these deaths are in developing countries. This total is greater than that due to malaria, AIDS and measles combined. Streptococcus pneumoniae has over 90 serotypes, out of which eight are included in the 10-valent Pneumococcal conjugate vaccine (Synflorix) currently in use in Kenya. Pneumococci are highly diverse and serotype prevalence is dynamic based on age, time period and geographical area. There is no published data on serotypes found in Nairobi and other areas in Kenya except the coastal region. It is therefore possible that these serotypes are different from those included in the vaccine, subjecting the immunogenicity of the vaccine among Kenyan infants to doubt. Since its launch for free public use in February, 2011increasing number of children has been immunized, yet, it was not clear to what extent the vaccine is protective. This study therefore evaluated the immunogenicity of the vaccine by measuring serum concentration of IgG antibodies among infants immunized with PCV-10 at the Mbagathi District Hospital (MDH). It also investigated; the vaccine herd effect on study infants biological mothers and factors that affect the vaccine immunogenicity. It was a cross-sectional study where infants that completed 3-doses of PCV-10 had IgG antibodies to serotype-specific capsular polysaccharide measured by enzyme-linked immunosorbent assay. The majority (76.1%) of the infants who had completed the required dose of the pneumococcal conjugate vaccine had IgG serum titres of between 0.34mg/dl to 0.36mg/dl. Thirteen percent of infants had 0.30mg/dl to 0.33mg/dl serum concentration of PD specific IgG antibodies. The remainder of the studied infants had IgG antibody titres ranging between 0.25mg/dl to 0.29mg/dl and ≤0.25mg/dl respectively. Also, the total score for serum concentration of PD specific IgG among study infants biological mothers was between 0.34 – 0.36 (61.6%), which meets the threshold set by WHO. This study also found out that there was multi-collinearity between IgG antibody levels (mg/dl) for infants and vaccinated infant’s biological mothers and several variables. These variables included: Use of alcoholic drinks by infants’ biological mother during pregnancy (r =.595,p ≤ 0.05); Maternal diet during pregnancy (r =.137,p ≤ 0.05); Breast feeding frequency (r =.220, p ≤ 0.05); Gap with other children (r =.133, p ≤ 0.05); Child hospitalization (r =.131, p ≤ 0.05); Chronic illness (r =.154, p ≤0.01); and IgG antibody levels (mg/dl)for infants (r =.675,p > 0.05). The 10-valent pneumococcal conjugate vaccine is immunogenic against Pneumococcal Disease four weeks after completion of three doses among infants attending child welfare clinic at Mbagathi District Hospital, Kenya.