Efficacy of Pfizer/BioNTech Covid vaccine slips to 84% after six months, data show

The efficacy of the Covid-19 vaccine developed by Pfizer and BioNTech fell from 96% to 84% over six months, according to data released Wednesday, a decline that could fuel Pfizer’s case that a third dose will eventually be required. The data, released in a preprint that has not been reviewed by outside scientists, suggest the vaccine was 91% effective overall at preventing Covid-19 over the course of six months. In the ongoing study, which enrolled more than 44,000 volunteers, the vaccine’s efficacy in preventing any Covid-19 infection that causes even minor symptoms appeared to decline by an average of 6% every two months after administration. It peaked at more than 96% within two months of vaccination and slipped to 84% after six months.