The magnitude of the increased risk of pneumococcal disease varies quite considerably by individual risk conditions. People who are unable to mount an adequate immune response to pneumococcal capsular antigens because of immunocompromised states caused by disease or therapy are at particularly high risk of IPD, some as much as up to 100 times greater than those with no risk conditions.3,31,32 Several studies have reported HIV infection and immunosuppressive therapy (e.g. after solid organ transplantation) as major factors associated with increased susceptibility to IPD.28,33-37 Other chronic diseases shown in these studies as strong risk factors for IPD include bronchial asthma, renal disease, chronic airway disease and diabetes mellitus.28,38 In addition, the incidence of pneumococcal disease is substantially higher among those with inherited conditions such as sickle cell disease and primary immunodeficiencies.27,39,40 There are also other chronic medical conditions that are important risk factors for IPD.41 In the Australian immunisation handbook the conditions for which risk factor-based pneumococcal vaccination recommendations apply are grouped into categories A and B based on their associated level of risk, and for that reason the recommendations vary between the two categories (Box).26
The incidence of IPD among Indigenous Australians is currently higher than that among non-Indigenous Australians for all age groups. Since the introduction of funded pneumococcal vaccination in early 2000, the IPD burden for Indigenous Australians has only decreased among children directly targeted for vaccination.42 Among Indigenous adults, including young adults, the total IPD incidence has increased, in contrast to that in the non-Indigenous population, in which substantial reductions were seen across all ages due to direct as well as good indirect (herd) impact of the childhood vaccination program. As a result, in the last decade or so the disparity of IPD incidence between Indigenous Australians and non-Indigenous Australians has widened. Currently, the lowest incidence of IPD among Indigenous adult age groups is in the 15 to 24 years age group and is comparable with the incidence among non-Indigenous adults aged 65 years and over.
Pneumococcal disease epidemiology in Australia
IPD has been a nationally notifiable disease in Australia since 2001. The National Notifiable Disease Surveillance System (NNDSS) captures all notifications of IPD in the country. In 2018 there were 2032 cases of IPD notified to NNDSS with, as in other years, episodes peaking in the winter months.43 There were 131 deaths in that year reported as being due to IPD, most among elderly adults. The incidence of IPD is highest in extremes of age, with about 18 per 100,000 population in children under 2 years of age and 25 per 100,000 population in adults aged over 85 years.44
In the 10 years after the rollout through the NIP of funded pneumococcal vaccination in 2005 for all children and older adults, the IPD incidence among all Australians halved.45 The decline of more than 80% in young children was particularly remarkable. The pneumococcal disease incidence among Indigenous Australians is several-fold higher than for non-Indigenous Australians. Of all IPD cases in 2018, 11% were in Indigenous people, who make up about 3% of the Australian population.43
Unlike for IPD, there are limited data available on the epidemiology of noninvasive pneumococcal disease. Among Australian adults aged 65 years and over, about 45,000 are hospitalised because of pneumonia annually. Of these, about 6300 (14%) have pneumococcal CAP. A further 1400 patients with pneumococcal CAP are managed by GPs.46,47