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Pfizer Passes the Test for Potency

Pfizer Inc and BioNTech said on Thursday their vaccine is around 91% effective at preventing COVID-19, citing updated trial data that included participants inoculated for up to six months. The shot also showed early signs of preventing disease in a small subset of study volunteers in South Africa, where a concerning new variant called B.1.351 is circulating. Although lower than the stunning 95% efficacy result reported from its 44,000-person clinical trial in November, overall efficacy of 91.3% shows the vaccine to be a powerful tool against an evolving virus. The virus now has more transmissible forms and those that have been shown to evade antibody protection in lab studies and real-world clinical trials. The data released on Thursday offered the first look at how the vaccine might work in people against the South African variant. Among a group of 800 study volunteers in South Africa, where the variant is widespread, there were nine cases of COVID-19, all of which occurred among participants who got the placebo. Of those nine cases, six were among individuals infected with the South African variant.  “The Pfizer data are a big deal,” said Shane Crotty, a virologist at the La Jolla Institute for Immunology in San Diego, noting that the results offer the first data in humans about how so-called mRNA vaccines such as Pfizer’s will perform against the South African variant.