Just read this news! It's pretty awesome news. These are interim results the final results are yet to be published but they are way above the FDA approval mark which wants atleast 50% efficacy from any vaccine. But yes it takes 28 days from start of vaccination for a person to become completely immune towards Covid-19. But I think Johnson's and Johnson's vaccine is much much better and as that vaccine has proven to have the least reactions and it's a one shot vaccine. But obviously the quicker the better in this situation.