with graphics showing how russia's vaccine would save the planet. >> translator: i know that our vaccine works effectively, forms a strong immunity. and i repeat, it has passed all the necessary checks. >> but that's not exactly true. every covid-19 vaccine candidate must go through at least three phases of human trials. phase one, is the drug safe for humans? a small number of brave volunteers try the drug to see if research should continue. phase two, an expanded number of volunteers take the vaccine, their health monitored regularly. and phase three, does it work on a large scale? tens of thousands of volunteers are given the vaccine to check for adverse reactions, which could be rare, but important