Invasive pneumococcal disease in Northern Alberta, not a Red Queen but a dark horse

The consequences of the introduction of various pneumococcal protein conjugate vaccines (PCV) for children and adults is poorly understood.

We undertook a population-based cohort study of invasive pneumococcal disease (IPD) in Northern Alberta (Canada) from 2000 to 2014, years spanning pre-and early PCV (2000-2004) vs PCV-7 (2005-2009) vs PCV-13 (2010-2014) time periods.

We collected clinical, laboratory, and Streptococcus pneumoniae serotype information on all patients from 2000 to 2014. We determined changes in presentation, outcomes, serotypes, and incidence in children and adults across time periods.

There were 509 cases of IPD in children, an 80% decrease over time. Rates of empyema (4.0-15.7%, p < 0.001), ICU admission (13.1-20%), and mortality (1.8-8.4%, p < 0.001) increased over time. There were 2417 cases of IPD in adults. Unlike children, incidence of IPD did not change nor did rates of empyema. ICU admissions increased (p = 0.004) and mortality decreased (18.7-16.5%, p = 0.002). The total number of serotypes causing IPD remained stable in children (22 vs 26 vs 20) while they decreased in adults (49 vs 47 vs 42).

For children, PCV vaccination strategies resulted in decreased overall rates of IPD and we observed increased rates of empyema and mortality; for adults, there was no change in IPD rates although disease severity increased while mortality decreased. On a population-wide basis, our results suggest that current PCV vaccination strategies are associated with an overall decrease in IPD but disease severity seems to be increasing in both children and adults.