Healthy people in their 20s have been asking me about getting the third shot of the Covid-19 mRNA vaccines, recently authorized for older people. I’ve advised caution. More vaccine isn’t always better.
Doctors think of drug dosing using the metaphor of a “therapeutic window.” The bottom of the window is the lowest effective dose. The top is the dose at which the side effects become unacceptable. We aim to keep the dose within the therapeutic window.