BACKGROUND: A new 10-valent pneumococcal conjugate vaccine (PCV10SII) was prequalified by WHO in 2019 for children based on non-inferiority of immunogenicity to PCV13 and PCV10GSK. However, the efficacy of PCV10SII against pneumococcal carriage or disease has not been compared with other PCVs. We compared the risk of seroinfection in PCV10SII with PCV10GSK and PCV13-vaccinated infants. METHODS: Data were available for 716 infants from two randomised trials comparing the immunogenicity of PCV10SII with PCV13 and PCV10GSK. Serotype-specific IgG levels were measured from serum samples collected at four weeks after the primary vaccination series and at the time of booster vaccination. We defined seroinfection as any increase in serotype-specific IgG between post-primary vaccination and the booster dose, indicating likely colonisation, subclinical infection, or disease. We compared the relative risk (RR) of seroinfection between PCVs. RESULTS: There was no difference in the risk of seroinfection between PCV10SII and PCV10GSK for the shared serotypes, but PCV10SII showed better protection against 6A and 19A, not included in PCV10GSK. Compared with PCV13, the risk of seroinfection was 65% lower in PCV10SII for serotype 14 (RR = 0.35, 95% CI: 0.22, 0.57), 2.27-fold (95% CI: 1.40, 3.68) and 2.91-fold (95% CI: 1.84, 4.60) higher for 6A and 6B seroinfection, and similar for the remaining serotypes. CONCLUSION: PCV10SII demonstrated comparable seroefficacy as PCV10GSK against colonisation by serotypes common to both and may offer better coverage in countries with high prevalence of 6A and 19A disease. The serotype-specific differences in seroefficacy between PCV10SII and PCV13 should be considered when evaluating cost effectiveness. Funding Gates Foundation (INV-056261_2023).