S110 The effect of PVC13 and PPV23 on nasopharyngeal colonisation following human pneumococcal challenge with serotype 3 and serotype 6b: the pneumo 2 study

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Background Serotype 3 (SPN3) remains a frequent cause of pneumococcal disease and colonisation globally. A lineage shift from clade 1a to clade 2 with differential protection by 13-valent pneumococcal conjugate vaccine (PCV13) potentially contributing. Methods Participants were randomised to PCV13, 23-valent pneumococcal polysaccharide vaccine (PPV23) or saline. Using a human challenge model, participants were inoculated with SPN3 at 1-month and serotype 6B (SPN6B) at 6-months post-vaccination. PCV13 and saline arms were also randomised to SPN3 clades 1a and 2. Following inoculation, colonisation status, density and duration were assessed for 23 days. The primary endpoint was the SPN3 colonisation ratio (clades combined), comparing each vaccine with saline. The above comparisons were performed for individual clades and SPN6B. Results 407 and 243 participants were included in the analysis for SPN3 and SPN6B, respectively. At 1-month post-vaccination, PCV13 resulted in a non-significant reduction of SPN3 colonisation (clades combined, PCV13 84/153[56%] vs saline 101/155[65%], RR 0.84[0.7–1.01], p=0. 068), and 29% reduction of SPN3 clade 2 colonisation (RR 0.71[0.54–0.91], p=0.009). No protection was observed for density. 6-months post-vaccination, PCV13 showed a 60% reduction of SPN6B colonisation (PCV13 13/81[16%] vs saline 31/78[40%], RR 0.4[0.22, 0.69], p=0.002), and a 5-fold reduction in colonisation density. PPV23 did not show protection against any of the above outcomes. Conclusions We found limited direct protection against SPN3 colonisation by PCV13 and no protection by PPV23. PCV13 protection against SPN6B persists for at least 6 months. Future evaluation of immune responses in blood and nasal mucosa will help identify correlates of protection against SPN3 colonisation.

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