AstraZeneca on Tuesday temporarily halted its phase three trials of a possiblevaccine after one participant suffered what may have been a serious adverse reaction. The vaccine "candidate" was developed by the pharmaceutical giant along with Oxford University and is currently being tested in large-scale human trials in the U.K., the U.S., Brazil and South Africa.
All of those trials have been put on hold to give scientists time to scrutinize data, and the individual who showed the possible adverse reaction, to determine whether it was, in fact, related to the drug.
"As part of the ongoing randomised, controlled global trials of the Oxford coronavirus vaccine, our standard review process was triggered and we voluntarily paused vaccination to allow review of safety data by an independent committee," a spokesperson for AstraZeneca said. "This is a routine action which has to happen whenever there is a potentially unexplained illness in one of the trials, while it is investigated, ensuring we maintain the integrity of the trials."
AstraZeneca did not provide details on what symptoms the participant had experienced, or when the trial was expected to resume. The spokesperson said they were expediting the review in hopes that it would not cause any drastic delays.
Dr. Mohamed Slaoui, the chief adviser to, told CBS News that the U.K.'s trial Data Safety Monitoring Board is "conducting an in-depth review of the company's vaccine candidate which is standard procedure when an adverse event occurs in clinical trials."
Dr. Jeff Pothoff, chief quality officer of University of Wisconsin Health, where one of the trials is being conducted, received the potential vaccine Wednesday, CBS affiliate WISC-TV reports. He noted that it's not unusual for trials to be paused.
"We don't know much more at this point. All these groups — AstraZeneca, Pfizer and Moderna — they have incredible attention to safety so if there is any whisper or wisp of something that would've gone wrong, or sometimes it's just related to regulatory issues," Pothoff said. "There's so much paperwork, and the i's dotted and t's crossed that they would stop the trial temporarily while they figure something out."
The Oxford University's vaccine team confirmed in a statement to CBS News that this is the second time the trials have been forced to pause due to a potential adverse affect. Earlier this summer another participant showed unexplained symptoms, triggering the same mandatory halt.
"The outcome of this review diagnosed the individual with an illness deemed unrelated to the vaccine," Oxford said, and the trial quickly resumed.
BBC News reported that the U.K.'s independent medical regulator, the MHRA, could once again allow the trials to resume in just a few days, if the participant's illness is diagnosed and found to be unrelated to the candidate vaccine.
AstraZeneca CEO Pascal Soriot said in a statement released Wednesday that the pause was company puts "science, safety and the interests of society at the heart of our work. This temporary pause is living proof that we follow those principles while a single event at one of our trial sites is assessed by a committee of independent experts. We will be guided by this committee as to when the trials could restart, so that we can continue our work at the earliest opportunity to provide this vaccine broadly, equitably and at no profit during this pandemic."
The Oxford/AstraZeneca vaccine is considered the leading candidate in the race to develop an effective COVID-19 vaccine. Oxford University has beentrials in the U.K., Brazil and South Africa. In , there was no evidence that the drug caused serious reactions.
Other vaccine candidates in phase three trials are being developed by Pfizer/BioNtech and Moderna. Russia skipped phase three testing of its potential vaccine. On Tuesday, the CEOs of nine drugmakers — AstraZeneca, BioNTech, , Johnson & Johnson, Merck, Moderna, Novavax, Pfizer and Sanofi — released a joint statement vowing not to release any vaccine unless proven safe by rigorous testing.
President Trump has claimed a vaccine could be ready as early as November, but his own health experts say that timeline is highly unlikely.