Invasive pneumococcal disease in Indigenous people in north Queensland: an update, 2005-2007

OBJECTIVE: To examine trends in invasive pneumococcal disease (IPD) in Indigenous people in north Queensland following the introduction of the 7-valent pneumococcal conjugate vaccine (7vPCV). DESIGN: Trends in IPD were compared over three 3-year periods: before the introduction of 7vPCV for Indigenous children (1999-2001), and two consecutive periods after its introduction (2002-2004 and 2005-2007). MAIN OUTCOME MEASURES: Incidences of IPD in Indigenous children and adults in 1999-2001 and 2005-2007; trends in IPD caused by 7vPCV and non-7vPCV serotypes; and trends in indirect protective effects and emergence of non-7vPCV serotype IPD. RESULTS: From 1999-2001 to 2005-2007, there was a 60% decline in IPD, with the virtual elimination of 7vPCV serotype IPD in young (< 5 years) Indigenous children. There is no evidence yet of an increase in non-7vPCV serotype IPD in these children. Although the annual incidence of IPD in Indigenous adults remained virtually unchanged, there was a 75% decline in 7vPCV serotype IPD in these adults (chi2(trend) = 11.65, P < 0.001). However, the incidence of IPD caused by non-7vPCV serotypes more than tripled in adults (chi2(trend) = 7.58, P = 0.006). Serotype 1 IPD has been prominent over the 9 years, but there is no evidence of a recent increase in serotype 19A IPD. CONCLUSIONS: Vaccinating Indigenous children with 7vPCV has protected Indigenous adults in north Queensland through an indirect "herd immunity" effect. However, this benefit has been offset by a recent increase in non-7vPCV IPD in Indigenous adults. Newer pneumococcal conjugate vaccines could prevent, both directly and indirectly, a considerable amount of the persisting IPD in Indigenous people in the region.