The statistics on efficacy are very preliminary, based on 94 cases out of 44,000 people in the clinical trial -- and based on only a couple of weeks of data. So it was 95% effective in preventing people from getting COVID in 2 weeks. What happens after 4 weeks, or 8 weeks, or 6 months?

Expect that efficacy number to drop dramatically, when people actually give it enough time to determine how many vaccinated people get it in the real world, over time, as the infection rate continues to rise.