Successful Control of Streptococcus pneumoniae 19A Replacement with a Catch-up Primary Vaccination Program in Taiwan

Streptococcus pneumoniae infections in Taiwan mostly occur in children aged 2-4 years. Because of a significant increase in the incidence of serotype 19A-related infections, the 13-valent pneumococcal conjugate vaccine (PCV13) was initially introduced in the national immunization program for children 2-5 years of age, prior to the national programs for infants. We have assessed the impact of such vaccination programs in reducing the incidence of invasive pneumococcal disease (IPD) in Taiwanese children. Methods: We analyzed the national data on IPDs from the Taiwan Centers for Disease Control between 2008 and 2017. We calculated the incidence rates of IPD and incidence rate ratios (IRRs) between years for different serotypes to estimate the effectiveness of the vaccination programs. Results: The national catch-up primary vaccination schedule successfully reduced the incidence rate of IPD from 17.8/100 000 in 2012 to 5.5/100 000 in 2017 among children aged 0-5 years. The IRR (2017 over 2012) was 0.31, corresponding to a 69% reduction. A modest herd effect was also observed, with a 37% reduction in the incidence of IPD in elderly people (≥70 years) from 2012 to 2017. The incidence of IPD caused by serotype 19A in children aged 0-5 years was reduced by 32.6-44.3% yearly from 2012 to 2017. In 2015, serogroup 15 outnumbered 19A, to become the leading serotypes in children 0-5 years old. Conclusions: Special catch-up vaccination programs starting from children 2-5 years of age with PCV13 have been highly effective in reducing the incidence of IPD, especially as caused by serotype 19A, in Taiwanese children.