The Oxford team in charge of the trial is at the forefront of the race to develop a working vaccine Trial volunteers should receive a second dose 28 days after their first, with regulations only allowing for a three-day grace period LONDON: Disruption to a US trial of the Oxford vaccine against the coronavirus disease (COVID-19) means it could miss a vital deadline to give its participants a secondary dose, it was revealed on Wednesday. Due to a month-long halt of the trial imposed by US regulators investigating potential side-effects, volunteers have only been given one dose of the vaccine and are in danger of missing out on the necessary booster shot, the Times newspaper reported. The Oxford team in charge of the trial is at the forefront of the race to develop a working vaccine, but could now face challenges in determining its effectiveness due to the pause in the US. Enrollment in other trials in several countries around the world, being run by AstraZeneca in conjunction with researchers at Oxford University, was put on hold in September, after a participant in its UK trial suffered a rare spinal inflammatory disorder known as transverse myelitis. While the British trial continued soon afterward — along with other testing in South Africa, Brazil, Japan and India — the American trial remains postponed. “There is quite a lot of evidence that a longer interval (between shots) is actually better ... However, changing the interval midway through a trial can be problematic. Anyone who doesn’t get their vaccinations according to the stated schedule should be excluded from the final analysis of the trial,” Eleanor Riley, professor of immunology at the University of Edinburgh, told the Times. “That means they may have to recruit additional people to make up the numbers. That will obviously add more delay to getting an answer. “If a large group is affected by the delay, they may analyze their data anyway, as a secondary subgroup analysis, to see if the difference in timing has any effect,” she added. Trial volunteers should receive a second dose 28 days after their first, with regulations only allowing for a three-day grace period. AstraZeneca declined to confirm how many participants had been injected in the US before the trial was paused when asked by the Times. However, AstraZeneca executive Mene Pangalos said the US trial was more of a confirmatory trial, according to a client note from Guggenheim. The note also said that the US pause would not have much bearing on the vaccine’s approval chances since it would ultimately be determined by the results of the other trials. And Prof. Robin Shattock of London’s Imperial College, who is developing a separate COVID-19 vaccine, told the Times that the gap in doses could improve protection from the disease. “The one month hold (for the US trial) likely reflects that the FDA (Food and Drug Administration) have not felt that they have been given enough information to allow the trial to restart,” he said.