D.H. Barouch

Figure 3. In the spring of 2020, the predominant global form of the original virus rapidly transitioned to a variant that carried four mutations in the SARS-CoV-2 genome, including a single D614G point mutation in the spike protein that conferred a fitness advantage.58,59 Subsequently, multiple waves of SARS-CoV-2 variants have emerged that replaced prior variants, with new variants often showing increased transmissibility and greater antibody escape (Figure 3).

Only a minority of people who use drugs ultimately become addicted — just as not everyone is equally at risk for the development of other chronic diseases. Susceptibility differs because people differ in their vulnerability to various genetic, environmental, and developmental factors.

In clinical studies of pharmaceuticals, we might see double-blind, randomized, phase 3 trials assessing outcomes, sometimes in thousands of participants followed over a period of many months or years.