Changes in invasive pneumococcal disease serotypes in a regional area of Australia following three years of 7vPCV introduction.

BACKGROUND Invasive pneumococcal disease (IPD) is a serious bacterial disease. Vaccination can prevent disease for many of the current serotypes. The aim of this investigation was to describe the notification rates of IPD in a regional area of Australia, explore changes in rates since the introduction of the population vaccine programmes in 2005 and to describe changes in the distribution of serotypes in relation to the available vaccines after three years. METHODS Annualized IPD notification rates were calculated for residents of a regional area in northern New South Wales. Rates were analysed according to serotypes covered by available vaccines. Changes in serotypes were compared for the periods 2002-2004 and 2008-2010. RESULTS The annualized notification rate of IPD in all ages for the period 2002-2004 was 13.7 per 100 000 population, and 8.3 per 100 000 population for the period 2008-2010 (rate ratio [RR], 0.61, confidence interval [CI]: 0.51-0.72). The largest decline was observed in 7-valent pneumococcal conjugate vaccine (7vPCV) types across all age groups (RR, 0.17, CI: 0.12-0.24) and in the zero to four year age group (RR, 0.03, CI: 0.01-0.11). The six serotypes included in the new 13-valent pneumococcal conjugate vaccine, but not in the 7vPCV, accounted for 40.6% of IPD cases in the zero to four year age group during the period of 2008-2010. DISCUSSION The introduction of 7vPCV significantly reduced the overall notification rate of IPD caused by the serotypes contained in this vaccine. This decline in IPD rates in children can be directly attributed to the use of 7vPCV, and in adults it is most likely an indirect effect of the 7vPCV programme in children.