| Methods |
Matched case‐control study |
| Participants |
Adults aged 18 years and above with indication for vaccination or above 65 years (n = 2108) |
| Interventions |
Cases (n = 1054) hospitalised with IPD from 1984 to 1990 (no previous pneumococcal disease) and pneumococcal isolate serotyped
Controls (n = 1054) selected from roster of hospitalised patients with no previous episode of IPD during the study period
Both 14‐valent and 23‐valent PPV |
| Outcomes |
B1. IPD (immunocompetent)
B2. Vaccine‐type IPD (immunocompetent and immunocompetent elderly) |
| Notes |
Matched 1:1 according to age, date and site of hospitalisation, condition of vaccination indication (duration, severity and number of illnesses)
Less cases were white (862/921) and had a private physician (829/903). More cases were residents and chronic care facility (181/117) and died during hospitalisation. Likely bias against vaccine effectiveness
Analysis according to indirect cohort method was conducted in a subgroup analysis of cases with a serotype contained in the 14 valent vaccine compared to non‐23 valent or 14 valent serotypes (23 valent non‐14 valent serotype cases excluded)
Vaccinated defined as receiving dose at least 2 weeks prior to selected hospitalisation |
| Risk of bias |
| Bias |
Authors' judgement |
Support for judgement |
| Random sequence generation (selection bias) |
High risk |
Non‐random study |
| Allocation concealment (selection bias) |
Low risk |
Study investigators determining participant inclusion unlikely to be aware of vaccination status |
| Confounding
All outcomes |
Low risk |
2/6 important confounding factors considered, however critical factors covered |
| Blinding of participants and personnel (performance bias)
All outcomes |
Unclear risk |
NA |
| Blinding of outcome assessment (detection bias)
All outcomes |
Low risk |
Due to specificity of outcome |
| Incomplete outcome data (attrition bias)
All outcomes |
Unclear risk |
Not described |
| Selective reporting (reporting bias) |
Low risk |
Limited extent to which analysis could have been manipulated to bias the findings |
