Background In settings with low routine coverage of pneumococcal conjugate vaccines (PCVs), mass campaigns targeting multi-age cohorts (MAC) might accelerate herd protection but would be costly. Mass campaigns using fractional dose PCV would decrease cost and increase access, but their effect on pneumococcal carriage is unknown.

Methods We conducted a cluster-randomized trial in Niger to evaluate the effect of mass campaigns on pneumococcal carriage. 63 villages were randomized in a 3:3:1 ratio to receive mass campaigns targeting children aged 1–9 years with a single full dose of Pneumosil, a single 1/5 fractional dose, or no campaign. We conducted surveys among 2268 households before and 6 months after vaccination. Data were collected about household composition and sociodemographics; a nasopharyngeal swab (NPS) was collected from a child aged 1–9 years. NPS were collected in STGG media and stored at -80°C within 8 hours of collection. Culture and Quellung reactions were performed in Kilifi, Kenya, in accordance with WHO-recommended procedures.

Results Pre-vaccination results are currently available; post-vaccination results will be available in September 2023. In the baseline survey, 2223 children were included, with median age of 4 years (IQR 2–6). Median household size was 7 (IQR 5–10), and a median of 4 people (IQR 2–5) slept in the same room as the child. 41% of children received 3 recorded doses of PCV in EPI, which increased to 80% when considering self-report. Baseline pneumococcal carriage prevalence was 87%, and the prevalence of vaccine-type (VT) carriage was 17%. Serotypes 19A, 19F, 23F, and 6A accounted for 74% of VT carriage. The most common non-VT serotypes isolated were 34, 11A, 23B and 16F.

Conclusion Eight years after PCV13 introduction, residual VT carriage was 17%, which is lower than expected. The effect of MAC mass campaigns on VT carriage will be known in September 2023.

Funding: EDCTP