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Introduction challenge trials
In human challenge studies (HCT) or Controlled Human Infection Models (CHIM), healthy volunteers are administered a pathogenic or virulent strain of a challenge agent, which can be a virus (ie influenza), bacteria (ie cholera) or a parasite (ie malaria).
In a historical context, the concept of challenge studies is not new. The experiments conducted by Louis Pasteur in the 19th century, where chickens were challenged with a weakened bacteria causing chicken cholera and immunized from further chicken cholera infection, can be seen as a type of challenge study. Human Challenge Trials have been performed in the United Kingdom since 1946 when the Medical Research Council established the Common Cold Unit (CCU) (also known as the Common Cold Research Unit [CCRU]) at Salisbury, Wiltshire. The aim was to undertake laboratory and epidemiological research on common colds in view of reducing human and economic costs.
Use of Human Challenge Trials
Human challenge trials are usually performed after phase 1 safety trials and are usually classified as phase 2 trials
In current drug / vaccine development human challenge trials can be used in a variety of ways, like dose-finding study, in preparation of field trials, but the most common use is that HCT are used as phase 2 proof-of-concept (PoC) studies.
These Human Challenge proof-of-concept trials designed to provide early evidence about efficacy and if a drug is likely to be successful in later clinical trial phases, and this is a short timeframe. Hence, PoC studies can guide drug developers to make smarter "go or no-go" decisions about if proceeding with larger, more expensive studies in the next stage of drug development. The results of PoC studies are critically pivotal for strategic decisions in early drug clinical trial development.
Human Challenge Trials have also previously been accepted as `preliminary clinical evidence` in the framework of Fast Track designation by the US Food and Drug Administration.
Due the reduced number of subjects needed for a Human challenge trials (40-60 subjects) compared to a classic `field` PoC trial (180-600 subjects), Human Challenge Trials forms a cheaper alternative. In addition their shorter duration allows for a quicker availability of efficacy data.
Use of Human Challenge Trials in raising funding
Seen their reduced cost and shorter duration phase 2 Human Challenge Proof of Concept trials are very helpful tool in supporting your company in raising funds, be it an additional fundings round with private investors, be it as initial clinical data used as basis for an Initial Public Offering (IPO).
In summary, the core attributes of a Human Challenge Trial compared to a traditional field trial are: