Level of Recall Bias Regarding Pneumococcal Vaccination History among Adults Hospitalized with Community-Acquired Pneumonia: Results from the University of Louisville Pneumonia Study

Background: Recall bias is likely to occur in vaccine effectiveness studies using self-reported vaccination history. The validity of patient-reported vaccination status for adults is not well defined. The objective of this study was to evaluate the validity of self-reported pneumococcal vaccination history among patients hospitalized with community-acquired pneumonia (CAP). Methods: Prospective ancillary study of a population-based observational study of hospitalized patients with CAP in the city of Louisville. To be included in the analysis, patients had to (i) be reached by phone 30-days after discharge from the hospital and (ii) report that they remembered whether or not they received a pneumococcal vaccine in the past five years. The vaccination history was classified as 1) Subjective: patient recollection, or 2) Objective: vaccination records from insurance companies or primary care physicians. Results: A total of 2,787 patients who recalled their vaccination history were included in the analysis. Subjective vaccination history was documented to be inaccurate in 1,023 (37%) patients. Conclusions: Our study indicates that in adult patients, self-reported data regarding pneumococcal vaccination is likely to be inaccurate in one out of three patients. This level of recall bias may incorporate a fatal flaw in vaccine effectiveness studies.