BACKGROUNDPneumococcus is a common cause of pneumonia, meningitis, and other serious infections in children. The previous study has proved that the 13-valent pneumococcal conjugate vaccine (PCV13) has sufficient immunogenicity in children. The data on long-term persistence of immunity will help the follow-up development work of pneumococcal vaccines.METHODSChildren who received the full vaccination course of the tested PCV13 in the previous clinical trial were enrolled again, and these who received other pneumococcal vaccines, or were infected with one or more serotypes of S. pneumoniae corresponding to PCV13 before enrollment were excluded. Participants were divided into four groups by age which is same as that of previous trial. The study lasted for 5 years, during which we measured pneumococcal antibodies of 13 serotypes included in PCV13 at particular points in time. Geometric mean concentrations (GMCs) and seropositive rates (the rate of IgG concentration ≥0.35 μg/mL) of antibodies against 13 serotypes were calculated.RESULTSFor the participants aged 2 months, five years after primary vaccination, except for serotypes 3 and 4, seropositive rates were 100%. GMCs of IgG antibodies against 13 serotypes ranged from 0.733 to 15.160 μg/mL. All of the participants aged 7-11 months had the serotype-specific IgG concentration ≥0.35 μg/mL four years after primary vaccination with the exception of serotypes 3, 4, 6 A and 9 V. IgG GMCs were 0.753-11.031 μg/mL. All participants aged 12-23 months and 2-5 years old had the serotype-specific IgG concentration ≥0.35 μg/mL three or two years after primary vaccination respectively, except for serotype 3. IgG GMCs ranged from 0.815 to 13.111 μg/mL, and 0.684 to 12.282 μg/mL respectively.CONCLUSIONPCV13 was applied to the population aged 2 months and 7 months - 5 years old with a good immune persistence, providing more extensive evidence of long-term efficacy for that vaccine.TRIAL REGISTRATIONThe trial was registered with ClinicalTrials.gov, number NCT06210737.