“It works effectively enough, forms a stable immunity and, I repeat, it has gone through all necessary tests,” Mr. Putin told a cabinet meeting Tuesday morning. Vaccines generally go through three stages of human testing before being approved for widespread use. The last phase, known as Phase 3, compares the vaccine to a placebo in thousands of people. This final phase is the only way to know with statistical certainty whether a vaccine prevents an infection. And because it’s testing a much larger group of people, a Phase 3 trial can also pick up more subtle side effects of a vaccine that earlier trials could not.

Source: New York Times August 11, 2020 11:15 UTC