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Reference.org
Human challenge study
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<p>A human challenge study, also called a challenge trial or controlled human infection model (CHIM), is a type of <a href="/facts/Clinical_trial/q8LMr832">clinical trial</a> for a <a href="/facts/Vaccine/QcXzLug2">vaccine</a> or other <a href="/facts/Drug/FFFUI9n4">pharmaceutical</a> involving the intentional exposure of the test subject to the condition tested. Human challenge studies may be ethically controversial because they involve exposing test subjects to dangers beyond those posed by potential <a href="/facts/Side_effect/PhuX2haY">side effects</a> of the substance being tested. Controlled human infection studies are also used to study viruses and immune responses. </p><p>During the mid 20th and 21st century, the number of human challenge studies has been increasing. A challenge study to test promising vaccines for prevention of <a href="/facts/COVID-19/YsUgvsaX">COVID-19</a> was under consideration during 2020 by several vaccine developers, including the <a href="/facts/World_Health_Organization/YNN3bgug">World Health Organization</a> (WHO), and was approved in the UK in 2021. </p><p>Over the second half of the 20th and the 21st centuries, vaccines for some 15 major pathogens have been fast-tracked in human challenge studies while contributing toward vaccine development to prevent <a href="/facts/Cholera/rk8JfWEp">cholera</a>, <a href="/facts/Typhoid_fever/bKPTIYLl">typhoid</a>, <a href="/facts/Flu_season/TdXdf0J1">seasonal flu</a>, and other infections. Since the 1980s, challenge trials which reported about <a href="/facts/Adverse_event/6zKwT4g5">adverse events</a> have had only 0.2% of patients with serious adverse events, and no deaths. According to <a href="/facts/Medical_ethics/Dm4TCznf">medical ethicists</a>, methods of conducting clinical trials by human challenge testing have improved over the 21st century to satisfy ethical, safety, and regulatory requirements, becoming scientifically acceptable and ethically valid as long as participants are well-informed and volunteer freely, and the trials adhere to established rigor for conducting clinical research. </p>