"Several articles published recently in the Journal of Evaluation in Clinical Practice raise important questions about how the efficacy and safety of COVID-19 vaccines have been and are being measured. First, Fung, Jones, and Doshi explained that statistical biases, particularly the case counting window bias, can greatly exaggerate the perceived effectiveness of COVID-19 vaccines in observational studies. A follow-up article by myself explained that this effect may be understated, due to the often accompanied definitional bias, and also that these biases could likewise exaggerate the perceived safety of COVID-19 vaccines in observational studies. Doshi and Fung then added further to the discussion by finding issues with case counting windows in COVID-19 vaccine clinical trials, relating to vaccine effectiveness. In this final article, I shall provide an example justifying my prior concern about counting windows in observational studies concerning safety, and further explain that there are also concerns around adverse effect counting windows in COVID-19 vaccine clinical trials, which may have exaggerated claims about vaccine safety."
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