AstraZeneca's Clinical Study on Hold After 'Unexplained Illness' - COVID-19 Clinical Trial
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AstraZeneca’s Clinical Study on Hold After ‘Unexplained Illness’

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    It’s not uncommon for clinical trials to be placed on hold, but with all eyes focusing on the progress of promising COVID-19 vaccines, AstraZeneca’s recent study freeze has garnered international headlines.  

    In early September, the company placed a hold on its COVID-19 clinical trials worldwide in response to a trial participant’s adverse reaction in the United Kingdom.  

    “We are working to expedite the review of the single event to minimize any potential impact on the trial timeline,” AstraZeneca said in a statement late Tuesday. “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.” 

    What is AstraZeneca’s Vaccine Candidate? 

    AstraZeneca’s vaccine candidate AZD1222 was developed by Oxford University scientists who are now working directly with AstraZeneca on development and production. It’s formulated with a weakened version of a common cold virus that has been genetically changed to make it impossible to grow in humans.  

    The AZD1222 construct also contains added genetic material, which is used to make proteins from the SARS-CoV-2 coronavirus called Spike glycoprotein. This protein exists on the surface of the virus and plays a critical role in the infection pathway of the coronavirus.  

    After vaccination with AZD1222, the surface spike protein is produced to prime the immune system to attack the first signs of COVID-19 if it ever infects the body. As a result, scientists hope that vaccination with AZD1222 will stop the coronavirus from entering human cells and ultimately prevent infection.  

    First Major Obstacle in Historic Vaccine Effort 

    The hold on AstraZeneca’s Phase 3 clinical trial of AZD1222 marks one of the first major obstacles in the company’s pursuit of a coronavirus vaccine.  

    However, it’s not entirely unexpected. During smaller Phase 1 and 2 trials, none of the COVID-19 vaccine candidates reported serious reactions or side effects. Large trials involve thousands of people, so it’s more likely for a rare reaction to occur. This is exactly why comprehensive Phase 3 clinical trials are required before FDA approval.  

    It’s worth noting that the unexplained illness that led to the pause of AstraZeneca’s clinical study occurred in only one participant, not multiple. It’s possible that the illness isn’t related to the vaccine at all, but its cause must be confirmed before the study can proceed.  

    “To have a clinical hold, as has been placed on AstraZeneca as of yesterday, because of a single serious adverse event is not at all unprecedented,” Francis Collins, the director of the National Institutes of Health, told a Senate panel on Wednesday.  

    “This certainly happens in any large-scale trial where you have tens of thousands of people invested in taking part, some of them may get ill and you always have to try to figure out: Is that because of the vaccine, or were they going to get that illness anyway?” 

    Now the Data Safety Monitoring Board, an external group of experts, will conduct an investigation. Once the participant’s illness is better understood, AstraZeneca will most likely be cleared to continue its Phase 3 trial to test the efficacy and safety of AZD1222.  


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