WASHINGTON: AstraZeneca Plc’s Covid-19 vaccine, which faced a fresh onslaught of questions this week, was 76% effective in a US study — a slightly downgraded estimate based on the latest data collected from a contentious clinical trial. The company issued the new analysis in a statement on Thursday after an independent monitoring board expressed concern that the initial efficacy of 79% relied on outdated information. The earlier reading was based on data gathered through February 17. The latest twist created another layer of uncertainty for a product already facing dwindling public support in Europe following months of confusion and missteps. The data glitch may delay the shot’s ability to win US regulatory clearance, although it will likely still play a crucial role in curbing the global pandemic. “The primary analysis is consistent with our previously released interim analysis, and confirms that our Covid-19 vaccine is highly effective in adults, including those aged 65 years and over,” said Mene Pangalos, the company’s executive vice president of BioPharmaceuticals research and development. “We look forward to filing our regulatory submission for Emergency Use Authorization in the US and preparing for the rollout of millions of doses across America.” The findings were based on 190 symptomatic cases that developed among the 32,449 volunteers who participated in the trial, which includes 49 cases that weren’t counted as part of the initial analysis. The company didn’t disclose how many of those cases occurred in the vaccine arm and how many in the placebo arm. There were 8 cases of severe disease, all in the placebo arm. In an unusual move earlier this week, a group of experts working with the company on the safety of its US clinical trial contacted government agencies late on Monday to express concern about data that AstraZeneca made public just hours earlier. The company responded by saying it would release fresh estimates within 48 hours. The vaccine developed with the University of Oxford protected all volunteers against developing severe disease or requiring hospitalization, according to the Cambridge, England-based company. Those aged 65 and older were 85% less likely to develop symptomatic disease if they received the vaccine in the study. The US trial data was deemed important because earlier numbers from research conducted in the UK and Brazil also sowed confusion by producing two different efficacy readings. Plus, those tests failed to include enough elderly people to establish efficacy for that crucial patient group.