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. 2013 Jan 31;2013(1):CD000422. doi: 10.1002/14651858.CD000422.pub3

Shapiro 1991.

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