Background It is vigorously debated whether pneumococcal polysaccharide vaccination (PPV) reduces risk of acute coronary syndrome (ACS) events in patients with community-acquired pneumonia (CAP).

Methods Clinical data were prospectively collected on a population-based cohort of adults presenting with CAP in Edmonton (Alberta, Canada). Multivariable Cox models and propensity matching were used to examine the association between PPV status and ACS events within 90 days of pneumonia. Sensitivity analyses related to PPV administration (before pneumonia vs after) and duration of benefit (90 days vs 1 year) were conducted to rule out confounding.

Results Overall, 6171 patients were included; mean age 59 (SD 21) years, 53% male subjects, 18% had ischaemic heart disease and 2738 (44%) were hospitalised. Within 90 days of pneumonia, ACS events occurred in 175 (3%) patients and most were non-fatal (162 (93%)). In multivariable analyses, PPV exposure was associated with a 58% reduction in ACS events (12 vs 16 events per 100 patient-years, adjusted HR (aHR) 0.42 (0.27 to 0.66)) and results were nearly identical with propensity matching (aHR 0.46 (0.28 to 0.73)). However, indepth sensitivity analyses, with some with large assumptions, could not refute the existence of a small protective benefit of PPV.

Conclusion Even after extensive adjustment using clinical data, the authors observed that PPV exposure was associated with a 60% reduction in ACS events among patients with pneumonia. Sensitivity analyses demonstrated that these findings, at least in part, were probably a result of confounding, most likely the ‘healthy-vaccinee’ effect. Previous observational studies using administrative data suggesting a very large protective benefit of PPV on ACS events may have been heavily confounded.