(Adnkronos) – Controlled Human Infection Models (CHIM), clinical studies in which carefully selected volunteers are deliberately exposed to controlled doses of pathogens, are now used in several European countries, while Japan remains cautious. Also known as ‘human challenge studies’, they are considered a more efficient way to evaluate the safety and efficacy of potential drugs compared to conventional methods. In Japan, however, fears related to risks – from the possibility of serious illnesses to long-term effects – fuel strong opposition, and the government maintains a cautious approach.
CHIM can shorten development times and reduce the number of participants, as they do not require waiting for volunteers to encounter the pathogen in daily life, as in traditional trials. In an interview at the end of August with Jiji Press and other media, Pierre Van Damme, director of Vaccinopolis – a clinical trial facility at the University of Antwerp – highlighted the value of CHIM. “If we had developed the vaccines earlier, we would have reduced mortality even further,” he stated regarding the Covid-19 pandemic. Vaccinopolis has 30 beds dedicated to CHIM, the largest capacity in the world.
Van Damme recalled that traditional clinical studies often recruit between 1,000 and 40,000 participants and last several years, while CHIM studies can reduce this to 20–200 volunteers within a few months. Vaccinopolis is currently conducting human challenge trials on therapies against infectious diseases such as influenza and malaria. To minimize risks, enrollment is generally limited to healthy adults between 18 and 40 years old. Participants are monitored 24 hours a day, with doctors ready to intervene in case of sudden changes in clinical conditions.
The United Kingdom announced in 2020 the launch of CHIM to accelerate the development of anti-Covid-19 vaccines, investing 33.6 million pounds in collaborations between universities and industry. Germany and the Netherlands also use these trials for some low-mortality infectious diseases. In Japan, however, ethical and safety concerns have slowed the introduction of CHIM. Some critics fear they might be perceived as “human experimentation.”
The government’s plan for promoting medical research and development, published in February, refers to “ethical and safety issues” and states that any introduction will be considered “with caution.” During a meeting of experts for drafting the plan, a specialist in vaccine safety assessment warned that CHIM involve “considerably high risks.” Recalling human experiments conducted by the former Japanese Imperial Army before and during World War II, another expert called the issue “sensitive for the Japanese people.”
The World Health Organization’s ethical guidelines published in 2021, however, emphasized the safety of CHIM, noting that in recent decades, studies have been conducted “with very few serious or lasting harms.” The WHO also reiterated that these researches, carried out according to rigorous ethical standards, must be distinguished from wartime human experimentation, an assessment that contrasts with the Japanese government’s position.
A Cabinet Office official involved in drafting the plan expressed concern about the risk of serious illnesses, emphasizing that it is “out of the question for a participant ( in a CHIM) to die.” An official from the Ministry of Health, Labour and Welfare, who is leading the discussion on the possible introduction of CHIM in Japan, warned that the decision “should not be taken lightly.” The ministry intends to first analyze international experiences, including those of Belgium, to identify specific safety and ethical issues.
