<p>US scientists are developing a strain of the coronavirus that could be used to deliberately infect volunteers in so-called "challenge studies," a government agency said Friday.</p>.<p>The work is preliminary and the government is continuing to prioritize randomized clinical trials of vaccine candidates, the National Institute for Allergies and Infectious Diseases (NIAID) said.</p>.<p>Several of these have entered their final stages, including the vaccines developed by Moderna, Pfizer and AstraZeneca.</p>.<p>But NIAID has nonetheless "begun efforts to manufacture a strain that could be used to develop a human challenge model, if needed," it said in a statement.</p>.<p>In normal clinical trials, volunteers receive either a medicine or a placebo and their health is then followed over the course of months of years.</p>.<p>Scientists look for how well the vaccine or treatment worked when the person was naturally exposed to the pathogen.</p>.<p>A quicker way to test whether a drug works is by deliberately infecting volunteers, as has been done in the past for influenza, malaria, typhoid, dengue fever, and cholera.</p>.<p>In the US, advocacy groups like 1DaySooner support challenge studies for Covid-19, but the subject is controversial because of how serious the disease can be and because its effects aren't fully understood.</p>.<p>NIAID said it would probably reach a decision toward the end of 2020, when the late-stage clinical trials that are underway start reporting their results.</p>.<p>This would help it determine whether challenge studies are needed, safe and ethical, it added.</p>.<p>David Diemert, the director of George Washington University's vaccine trial research unit who is overseeing a trial of Moderna's vaccine in the US capital, told AFP he did not think challenge trials were appropriate for Covid-19.</p>.<p>"I think they're a critical tool, but only under the right circumstances," he said.</p>.<p>Diemert is himself leading a challenge trial into a hookworm vaccine.</p>.<p>But he said that for Covid-19, "we don't have a very clear understanding of who is at risk of developing severe disease and we have no treatment that is guaranteed to cure someone if they do develop severe disease."</p>.<p>There's also enough widespread community transmission in the US -- the worst hit country in the world with 5.3 million confirmed cases -- to mean challenge trials are not necessary, he added.</p>
<p>US scientists are developing a strain of the coronavirus that could be used to deliberately infect volunteers in so-called "challenge studies," a government agency said Friday.</p>.<p>The work is preliminary and the government is continuing to prioritize randomized clinical trials of vaccine candidates, the National Institute for Allergies and Infectious Diseases (NIAID) said.</p>.<p>Several of these have entered their final stages, including the vaccines developed by Moderna, Pfizer and AstraZeneca.</p>.<p>But NIAID has nonetheless "begun efforts to manufacture a strain that could be used to develop a human challenge model, if needed," it said in a statement.</p>.<p>In normal clinical trials, volunteers receive either a medicine or a placebo and their health is then followed over the course of months of years.</p>.<p>Scientists look for how well the vaccine or treatment worked when the person was naturally exposed to the pathogen.</p>.<p>A quicker way to test whether a drug works is by deliberately infecting volunteers, as has been done in the past for influenza, malaria, typhoid, dengue fever, and cholera.</p>.<p>In the US, advocacy groups like 1DaySooner support challenge studies for Covid-19, but the subject is controversial because of how serious the disease can be and because its effects aren't fully understood.</p>.<p>NIAID said it would probably reach a decision toward the end of 2020, when the late-stage clinical trials that are underway start reporting their results.</p>.<p>This would help it determine whether challenge studies are needed, safe and ethical, it added.</p>.<p>David Diemert, the director of George Washington University's vaccine trial research unit who is overseeing a trial of Moderna's vaccine in the US capital, told AFP he did not think challenge trials were appropriate for Covid-19.</p>.<p>"I think they're a critical tool, but only under the right circumstances," he said.</p>.<p>Diemert is himself leading a challenge trial into a hookworm vaccine.</p>.<p>But he said that for Covid-19, "we don't have a very clear understanding of who is at risk of developing severe disease and we have no treatment that is guaranteed to cure someone if they do develop severe disease."</p>.<p>There's also enough widespread community transmission in the US -- the worst hit country in the world with 5.3 million confirmed cases -- to mean challenge trials are not necessary, he added.</p>