Pfizer's COVID-19 vaccine effectiveness drops after 6 months: studyOctober 5 2021https://www.ctvnews.ca/health/coronavirus/pfizer-s-covid-19-vaccine-effectiveness-drops-after-6-months-study-1.5612595
October 5 2021https://www.ctvnews.ca/health/coronavirus/pfizer-s-covid-19-vaccine-effectiveness-drops-after-6-months-study-1.5612595
