Thread by @nataliexdean

What is the best endpoint for Phase 3 vaccine trials? Disease of any severity? Severe disease? Infection? Most trials have selected the first, but this @PostOpinions piece is critical of counting mild cases. A thread in defense of what is being done. 1/6
washingtonpost.com/opinions/2020/…

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
who.int/blueprint/prio…

Similarly, the FDA's guidance to industry was released in June. It states that either disease or infection are acceptable endpoints. 3/6
fda.gov/media/139638/d…

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

This reflects one of many trade-offs regulators assess when evaluating evidence from trials. Particularly in the setting of an emergency, does the need for conclusive efficacy against severe disease outweigh the need for timely action? 5/6
stm.sciencemag.org/content/11/499…

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