oa Southern African Journal of Epidemiology and Infection - Evidence that prevention of carriage by pneumococcal capsular vaccines may be the mechanism of protection from pneumococcal pneumonia : Festschrift
During the 1970s, a hexavalent pneumococcal polysaccharide vaccine (PPV-6) and a 13-valent (PPV-13) trial involving ∼12,000 Witwatersrand gold miners showed efficacy against pneumonia caused by vaccine types (VTs). The effect of PPV-6 and PPV-13 on nasopharyngeal carriage of pneumococcal serotypes in 600 and 200 miners, respectively, was evaluated, but was not previously published. Participants were randomised to receive PPV, meningococcal Group A vaccine (MVA) or saline placebo. Nasopharyngeal swabs were collected for pneumococcal serotype detection immediately before vaccine or placebo administration, one and 25 days after, and at the time of leaving the mine. Because PPVs failed to protect against serotype 3 carriage, analysis was confined to other VTs. PPV-6 caused a 70% reduction in percentage of VT carriage in PPV-6 recipients (6 VTs [6.9%] and 149 non-vaccine types [NVTs], versus 33 VTs [22.9%] and 111 NVTs in the MVA group [p<0.001]). A 70% reduction was also demonstrated when compared with carriage in placebo group (26 VTs [23.0%] and 87 NVTs [p<0.002]). In the PPV-13 study, there were six VTs (18.2%) in PPV-13 recipients and 10 VTs (35.7%) in the MVA group, resulting in a non-significant (p=0.15) 49% reduction in carriage. A 65% reduction in carriage (p=0.0054) was demonstrated when 51% carriage (18 VTs) in the placebo group was compared with 18.2% VT carriage in PPV-13 vaccinees. Data are consistent with the hypothesis that the impact of PPVs on pneumonia may be mediated through protection from carriage.
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