In a matter of days, health care workers in the U.S. will begin administering the nation’s third COVID-19 vaccine — one from Johnson & Johnson — in a major boost to vaccination efforts that will more quickly save lives. Clinical trials showed the vaccine was overall 66% effective at preventing moderate to severe COVID-19 in the lab as early as 14 days after getting jabbed. Specifically in the U.S., efficacy jumped to 72%.