"1 INTRODUCTION
Kaiser Fung, Mark Jones, and Peter Doshi1 raised some important points in their recent article published here in the Journal of Evaluation in Clinical Practice, on potential biases that could be exaggerating the effectiveness of the messenger RNA (mRNA) COVID-19 vaccines. In this reply paper, I highlight how an example they provided can be improved, in order to avoid underestimating the effect of their proposed case-counting window bias, and expand on their discussion around the potential impacts of case-counting window biases.
2 CASE-COUNTING WINDOW BIAS
Fung et al.1 correctly explain that in the clinical trials, 'Investigators did not begin counting cases until participants were at least 14 days (7 days for Pfizer) past completion of the dosing regimen, a timepoint public health officials subsequently termed ‘fully vaccinated’'... They present an example, in their Table 1, detailing how this bias can give the perception that a completely ineffective vaccine is 48% effective. As expected, the result is now more pronounced, with a vaccine with 0% effectiveness perceived as having 65% effectiveness."
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