Effectiveness of a Single Dose of Pneumococcal Conjugate Vaccine Against Invasive Pneumococcal Disease in Children: A Systematic Literature Review

While pneumococcal conjugate vaccines (PCVs) are typically administered to infants using a three- or four-dose regimen, children may receive less immunogenic regimens due to missed doses or alternative schedules. The level of direct protection in children vaccinated with a single dose of PCV remains unclear. We performed a systematic review of observational studies published during 2000-2024 on vaccine effectiveness (VE) of a single dose of PCV7, PCV10, or PCV13 against vaccine-type invasive pneumococcal disease (IPD) in children. Results were stratified by vaccine and age at administration, and meta-analysis performed to generate pooled VE estimates. Twenty-seven studies met the inclusion criteria: nine reported VE for PCV7, four for PCV10, seven for PCV13, and seven reported VE separately for more than one PCV. For PCV7, pooled VE was 64.6% (95% CI 47.3, 76.2) when administered < 12 months or age unspecified and 81.6% (95% CI 72.5, 87.7) when given ≥ 12 months. For PCV10, pooled VE was 73.0% (95% CI - 29.4, 94.4) when age at vaccination was unspecified, and one study reported 68.0% (95% CI 17.6, 87.6) VE when administered ≥ 12 months. For PCV13, pooled VE was 56.8% (95% CI 44.1, 66.6) when administered < 12 months or age unspecified, and 79.2% (95% CI 65.5, 87.5) when given ≥ 12 months. Available evidence demonstrates that a single dose of PCV provides protection against vaccine-type IPD, especially when administered after age 12 months. While complete vaccination according to licensed schedules provides optimal protection, our findings support single-dose catch-up programs for toddlers. Potential single-dose strategies for infants in humanitarian emergencies warrant further exploration.