Early impact of pneumococcal conjugate vaccine on invasive pneumococcal disease in Singapore children, 2005 through 2010

Background: In a previous study covering the period 1998-2004, we estimated the incidence of invasive pneumococcal disease (IPD) in Singapore to be 13.6 per 10(5) children aged <5 years, and determined that the 7-valent pneumococcal conjugate vaccine (PCV-7) would provide 78.1% serotype coverage for children aged <5 years. In the present study we sought to determine whether incidence and serotype trends have changed and to estimate pneumococcal vaccine coverage.

Methods: We retrospectively reviewed IPD cases from 2005 to 2010 and calculated separate serotype proportions and population-based incidence rates for 2005-2007 (early PCV period) and 2008-2010 (late PCV period). PCV-7 coverage was obtained from the National Immunisation Registry, and patients with PCV-7 vaccine-type IPD (VT IPD) and non-vaccine-type IPD (non-VT IPD) were compared.

Results: One hundred and eighteen patients, with a mean age of 46 months, were identified during 2005-2010. The incidence rate of IPD increased to 14.8 (for 2005-2007) and 15.2 (for 2008-2010) per 10(5) children <5 years, despite a gradual increase in PCV-7 coverage to approximately 45% of the birth cohort receiving one or more doses of PCV-7. Although IPD due to serotypes 6B and 19A increased, there was a concomitant reduction in other serotypes. Coverage by PCV-7 progressively declined from 78.6% in 2005-2007 to 64.4% in 2008-2010 for children aged <5 years.

Conclusions: Although population coverage with PCV-7 has risen, it remains suboptimal and the incidence of IPD remains unchanged. Furthermore, significant serotype changes (especially increases in 19A) have occurred. We need to adopt newer PCVs with broader serotype coverage and increase the number of children vaccinated as a matter of urgency.