First, this has been the plan for a while now. The WHO target product profile for covid vaccines was published in April, and lists that efficacy can be evaluated with respect to disease, severe disease, shedding, or transmission. 2/6
https://www.who.int/blueprint/priority-diseases/key-action/WHO_Target_Product_Profiles_for_COVID-19_web.pdf
Similarly, the FDA's guidance to industry was released in June. It states that either disease or infection are acceptable endpoints. 3/6
https://www.fda.gov/media/139638/download
The FDA notes the importance of assessing efficacy against severe disease, but they recognize that trials may not be adequately powered to do so. As long as it takes to observe a certain number of infections, it takes much longer to observe the same number of severe cases. 4/6
These are important discussions, but the time to have them was months ago. Trials are well underway now. I will be paying close attention to the secondary endpoint data generated by these trials, but I think it's helpful to explain why trials have been set up this way. 6/END
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