Oxford University and AstraZeneca’s COVID-19 vaccine could be up to 90 percent effective in treating the disease—a discovery made by mistake. Patients were supposed to be given two full doses of the vaccine during the trial, served four weeks apart. However, some participants were mistakenly given a half dose at first, and then the full dose later. Of those given two full doses, the vaccine had 62 percent efficacy, compared to 90 percent for the group given the smaller initial dose. “The reason we had the half dose is serendipity,” said Mene Pangalos, AstraZeneca’s vice president for biopharmaceuticals research and development. While Pfizer and Moderna’s vaccines have higher efficacy rates, with both proving 95 percent effective in trials, AstraZeneca’s vaccine will be cheaper and available for storage at warmer temperatures, according to the Associated Press.