Over 22,000 IPD patients in England (March 2002-March 2009 - aged 2 and over) were linked to their hospitalisation records. The prevalence of risk factors in these patients was compared to the prevalence of risk factors in the general population.
There was an increased odds ratio (OR) for hospitalisation (OR 11.7 2-15 years; 7.6 16-64; 2.7 65+) and death (OR 2.4 2-15 years, 3.9 16-64, 1.2 65+) from IPD among risk group. The most important risk factors that predict IPD are chronic liver disease, immunosuppression, and chronic respiratory diseases. Herd protection effects due to introduction of the 7-valent vaccine were identical in both patient groups as shown by the similar decline in the proportion of IPD caused by PCV7 serotypes in risk and non-risk groups.
There is a marked increased risk of IPD among those with certain clinical conditions, suggesting potential benefit from a targeted vaccination approach. However, the indirect protection from conjugate vaccination of children suggests PCV vaccination of high-risk groups may not provide substantial additional benefit once herd immunity takes effect.