Johnson & Johnson says its vaccine appears to protect against COVID-19 with just one shot. It’s not as strong as some two-shot rivals but still potentially helpful for a world in dire need of more doses. Results released Friday show the single-shot vaccine was 66% effective overall at preventing moderate to severe illness, and much more protective against the most serious symptoms. The vaccine worked better in the U.S. compared to South Africa, where it was up against a tougher, mutated virus.. The company says it will file an application for emergency use soon in the U.S., and then abroad.