To the Editor: The pattern of invasive pneumococcal disease (IPD) in Western Australia varies from that described in northern Queensland in a recent article by Hanna and colleagues.1 Their study showed a decline in IPD caused by serotypes included in the 7-valent pneumococcal conjugate vaccine (7vPCV) among Indigenous children and adults after the introduction of the vaccine in north Queensland. Over the same period, there was an increase among Indigenous adults in cases of IPD caused by serotypes not covered by the vaccine. However, the authors reported that there had been no increase in IPD caused by serotype 19A, a non-7vPCV serotype that has been increasingly predominant in other populations.2,3 In contrast to the disease pattern in north Queensland, serotype 19A has become the predominant disease-causing serotype in Western Australia, particularly among non-Indigenous people.

Data from the WA Notifiable Infectious Diseases Database show that the incidence of IPD in WA fell from 10.7/100 000 in 2001 (n = 203) to 6.3/100 000 in 2007 (n = 132). In children aged < 5 years, there was a significant drop in overall IPD rate, attributable to the decline in disease caused by 7vPCV serotypes, among both Indigenous children (from 70/100 000 to zero) and non-Indigenous children (from 50/100 000 to 1.6/100 000) (Box). The rate of IPD caused by 7vPCV serotypes also declined among Indigenous and non-Indigenous adults, suggesting a herd immunity effect.

From 2001 to 2007, the proportion of IPD cases caused by non-7vPCV serotypes increased among children aged < 5 years (from 19% to 91%) and children ≥ 5 years (from 33% to 72%). Serotype 19A was the only serotype that became more predominant, being responsible for 11 (8%), 14 (10%) and 26 (20%) cases of ICD in 2005, 2006 and 2007, respectively. In 2001, it accounted for 2.5% of cases in children < 5 years (1.6/100 000) and 0.8% of cases in children ≥ 5 years (0.1/100 000). By 2007, these figures had increased significantly to 34% of cases in children < 5 years (7.8/100 000) and 25% of cases in children ≥ 5 years (0.8/100 000). Interestingly, the increase in serotype 19A cases was seen only in non-Indigenous people (particularly children), with the number of cases remaining stable among Indigenous adults and children. Although numerous reports describe increasing prevalence of penicillin-resistant 19A strains,3,4 none of the WA isolates were penicillin-resistant.

In summary, after the introduction of the 7vPCV, the rate of IPD caused by 7vPCV serotypes decreased significantly in WA. However, the rate of IPD caused by serotype 19A, a non-7vPCV serotype, increased in non-Indigenous people and in the population overall.

These early trends have significant public health implications for vaccine policy. State and territory vaccination programs exist within the framework of the national immunisation program. However, jurisdictional expert advisory groups need local ongoing post-marketing surveillance, coupled with an understanding of historical trends and emerging serotypes, when formulating vaccine recommendations for their populations.

Incidence of invasive pneumococcal disease (IPD) caused by serotypes included in the 7-valent pneumococcal conjugate vaccine (7vPCV), by age group and Indigenous status, Western Australia, 2001–2007

* The 7vPCV was funded for Indigenous children from July 2001 and for all Australian children from January 2005.