Johnson & Johnson's single-dose COVID-19 vaccine has passed an important benchmark, with the FDA declaring it safe and effective. According to trial data, the vaccine is 66% effective overall, 86% effective at preventing severe illness, and fully effective at preventing hospitalizations and deaths. While it's less effective than the Pfizer and Moderna vaccines, it had two key advantages - it requires only a single shot, and can be stored long-term in normal refrigerators rather than ultra-cold s