Wednesday, August 5, 2020

Coronavirus – clinical trials #2

My previous post posited that the logical basis of clinical trials is Mill’s Method of Difference. The following is a simple example of a clinical trial based on Mill’s Method of Difference. Suppose there are N patients with disease D and the clinical trial is to treat some, e.g. two-thirds, of the N patients with medicine M and give the other one-third a placebo. Assume the later result is that the patients who are given M are cured of D, but the patients who are given the placebo are no better off than at the start. Then one could conclude that M is a cure for D. Call this the SDMT (for simple disease medicine trial).

A real world clinical trial is probably rarely as clear-cut as SDMT. It also seems to me that a clinical trial for a vaccine against the coronavirus would be far less clear-cut, for at least the following reasons.

1. The SDMT has a huge advantage over the coronavirus vaccine trial at the start. The participants at the start of the vaccine trial presumably have all tested negative for the coronavirus.* Some get the vaccine and the rest get a placebo. Then they wait to see if they do become infected by the virus to some degree. If they do become infected, and the vaccine protects against Covid-19, whereas those given the placebo get Covid-19, then the vaccine justifiably worked. However, many of the participants may not become infected any by the virus. They provide no basis for any conclusion about the efficacy of the vaccine. Presumably, such a vaccine trial must have many, many more participants than a SDMT kind of trial to make up for the probability of not becoming infected.

2. Those given the placebo might get infected, but their natural immune system might protect them from testing positive for the coronavirus or getting very ill from Covid-19 anyway.

3. Some participants may become only mildly infected and others far more so. This might come about due to the extent of precautions they take while in the trial, such as wearing a mask, keeping a safe distance from others, and washing hands. 

4. Some given the vaccine may be infected and the vaccine works. Others given the vaccine may be infected and the vaccine doesn't work or works poorly.

For all these reasons, and more not stated, a clinical trial for a coronavirus vaccine falls far short of all factors being the same except for one key difference for ideally applying Mill’s Method of Difference. It makes me quite skeptical about achieving a “gold standard” vaccine clinical trial per the wishful Dr. Anthony Fauci.

*The trial might also include groups of people who tested positive and are (a) asymptomatic or (b) have mild symptoms. They should be considered as separate trials.

No comments:

Post a Comment