"1. Introduction
Considerable attention has been given to the reported high efficacy for the Covid-19 vaccines in observational studies and randomised control trials, and how many of these studies have exhibited signs of measurement biases and confounding. One major kind of bias takes the form of miscategorisation, whereby study participants who have been vaccinated are miscategorised as unvaccinated up to and until some arbitrarily defined time after vaccination occurred (typically up to 14 or 21 days). This bias, which has been seen to take several different types, all of which help exaggerate vaccine efficacy, has recently become known colloquially as the ‘cheap trick’.
To identify the different types of miscategorisation bias and evaluate how widespread it is, we conducted a review of Covid-19 observational vaccine studies to identify those studies that have employed miscategorisation bias and we have simulated the effects of this bias on measures of vaccine efficacy.
This review reveals that, up to February 2024, 37 observational studies and randomised control trials on Covid-19 vaccines have employed different types of this bias, with variants including straightforward miscategorisation from one category to another, miscategorising the vaccinated as having unverified vaccination status, uncontrolled reporting of vaccination status and excluding those vaccinated from the study. Many of the studies have applied one or more of these biases within time periods from one week to three...
6. Conclusions
Our review reveals that a serious form of bias, miscategorisation, is pervasive throughout the many research studies that aim to measure Covid-19 vaccine efficacy. The effect of this bias is to artificially inflate vaccine efficacy and present the misleading impression that these vaccines are effective and that the non-vaccinated suffer from higher Covid-19 infection rates compared to the vaccinated.
We presented a simulation model to demonstrate the effects of this bias and show it artificially boosts vaccine efficacy in all cases, and with the application of repeated ‘booster’ vaccinations, the efficacy of repeated Covid-19 vaccines could be maintained at artificial levels in perpetuity should boosting be continued indefinitely. This effect occurs with a both a zero-efficacy (placebo) vaccine and a negative- efficacy vaccine that increases, rather than reduces, infection rates in those vaccinated.
This miscategorisation is guaranteed to lead to initially very high efficacy claims (usually above 90%) during peak vaccine rollout even if the vaccine were a placebo or worse. Efficacy then falls toward zero a few weeks later. This pattern of high initial efficacy, tapering off after 3 months is also consistently observed in real-world studies, and is often used as justification for additional, booster vaccinations to maintain efficacy. The corresponding Covid-19 infection rate is also likewise artificially elevated in the unvaccinated cohort compared to the vaccinated cohort. These issues apply to other measures of vaccination effectiveness related to mortality and morbidity.
Thus, we conclude that any claims of Covid-19 vaccine efficacy based on these studies are likely to be a statistical illusion or are exaggerated."
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