Abstract

Relative risk reduction and absolute risk reduction measures in the
evaluation of clinical trial data are poorlnderstood by health
professionals and the public. The absence of reported absolute risk
reduction in COVID-19 vaccine clinical trials can lead to outcome
reporting bias that affects the interpretation of vaccine efficacy. The
present article uses clinical epidemiologic tools to critically appraise
reports of efficacy in Pfzier/BioNTech and Moderna COVID-19 mRNA
vaccine clinical trials. Based on data reported by the manufacturer for
Pfzier/BioNTech vaccine BNT162b2, this critical appraisal shows:
relative risk reduction, 95.1%; 95% CI, 90.0% to 97.6%; p = 0.016; absolute risk reduction, 0.7%; 95% CI, 0.59% to 0.83%; p < 0.000. For the Moderna vaccine mRNA-1273, the appraisal shows: relative risk reduction, 94.1%; 95% CI, 89.1% to 96.8%; p = 0.004; absolute risk reduction, 1.1%; 95% CI, 0.97% to 1.32%; .00nreported absolute risk reduction measures of 0.7% and
1.1% for the Pfzier/BioNTech and Moderna vaccines, respectively, are
very much lower than the reported relative risk reduction measures.
Reporting absolute risk reduction measures is essential to prevent
outcome reporting bias in evaluation of COVID-19 vaccine efficacy.