Pfizer says its coronavirus vaccine is effective up to 6 months after use Print article NEW YORK — Pfizer says its vaccine continues to be effective against COVID-19 up to six months later. Pfizer and its German partner, BioNTech, announced updated results Thursday from their ongoing late-stage study of more than 44,000 volunteers. The companies said the vaccine was 91% effective against symptomatic disease and was even more protective in preventing severe disease. Of 927 confirmed COVID-19 cases detected through March 13, 77 were among people who received the vaccine and 850 were among people who got dummy shots. [ ] There were no serious safety concerns and the vaccine also appeared to work against a variant first detected in South Africa, the companies said.