Regulatory Studies avoid Bias Effects
Regulatory studies of vaccines go to great lengths to ensure that there are no bias effects. In the case of the study: those who think they have been vaccinated and feel safe usually behave more carelessly afterwards than unvaccinated persons or vaccinated persons from the control group who received the placebo and do not know what they were injected with. The difference in behavior would then be superimposed on vaccination effects, and it would be unclear what contributed what to the effectiveness. Therefore, these studies are randomized and double-blind. Thus, neither subjects nor physicians know whether the real vaccine or the placebo is administered. Furthermore, the control group – i.e. those who do not receive the vaccine being studied – is not only administered a saline solution, but also, for example, a vaccine against another disease. In AstraZeneca's pivotal study, for example, a combination vaccine against meningococcus was used in part. As a result, there are no systematically different reactions to the injection. Otherwise, conclusions could be drawn from the (non-)occurrence of reactions (such as fever, headache or chills) as to whether one is in the placebo group or not. In addition, there are other measures, such as taping the syringes, so that it is not possible to draw conclusions about the injected substance on the basis of the color.
Based on the effort expended, one can assume that the control and experimental groups do not behave significantly differently and compare the infection rates of the two groups. In very simplified terms, an estimator for vaccine effectiveness can then be found using the following equation:
EImpf = 1 - AExperimantal / AKontroll
where AExperimantal is the proportion of infected people among the vaccinated and Akontroll is the proportion of infected people among the unvaccinated. A vaccine effectiveness of 90 percent then means that the proportion of infected people among the vaccinated is only one tenth of the proportion of infected people in the control group.