Coronavirus vaccine: why it's important to know what’s in the placebo

Some researchers conducting clinical trials on a COVID-19 vaccine have not revealed to the public what the placebo contains, but they should. This is because the placebo ingredients influence how effective or harmful the active treatment, with which the placebo is compared, appears. Our new guideline published in PLOS Medicine remedies this problem by providing a template for reporting what’s in placebo controls. In some COVID-19 vaccine trials, participants in the control group (the group receiving a placebo) are injected with a saline solution. In other trials, they receive an actual treatment. For example, in the COVID-19 vaccine developed by the University of Oxford, the control group receives a meningitis and septicaemia vaccine as a placebo.