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A Vaccine Challenge Trial?

Yesterday Richard Engel NBC National News, announced that scientists at Oxford's Jenner Institute in the UK are currently discussing a Challenge Trial of their Oxford AstraZeneca vaccine.  The vaccine is now in Phase 3 Clinical Trials in multiple countries.  There are many ethical arguments against a Challenge Trial in which all volunteers are vaccinated, and then several months later are given a measured, calculated dose of SARS-CoV-2 virus.  Oxford could enroll 40-60 volunteers and determine vaccine effectiveness in much less time. They say the Challenge Trial, which would be done in healthy 20 year olds, will have "minimal risks."  Vaccine Challenge Trials raise ethical questions, but were done previously for other pathogens. The problem in this instance, is the lack of effective treatment for those volunteers who do develop Covid-19?

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Oxford AstraZeneca's standard Phase 3 randomized control trial is enrolling 30,000 volunteers - half will receive the vaccine and half will receive placebo.  No one including the patient will know what each volunteer receives until the end of the trial.  But if the volunteers aren't regularly exposed to the virus, it will take months to figure out the effectiveness of the vaccine.  Trial participants are told to lead their normal lives, but the trial will depend on them being exposed where virus infections are high.  The success of the vaccine is based on the number of cases of Covid-19 in the vaccinated group vs the placebo group.  In the US Moderna and Pfizer are also in Phase 3 testing with 30,000 volunteers.


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