A new study registered with ClinicalTrials.gov is deliberately exposing healthy adults to a live influenza A(H3N2) virus in Canada. Health Canada’s Biologic and Radiopharmaceutical Drugs Directorate has approved the H3N2 challenge strain for use in humans specifically for the purposes of the study. The study is not evaluating a vaccine or other biologic, rather it’s looking at the influenza infection model “to identify a dose that reliably produces mild-to-moderate influenza illness and to collect the safety, virological and immune-response data needed to use the model in future vaccine studies.” The purpose is to create a model that will allow for human infection studies.1
In the United States, the National Institutes of Health (NIH) has supported similar research since at least 2019 through National Institute of Allergy and Infectious Diseases (NIAID) sponsored clinical trial units.2 The University of Maryland’s Center for Vaccine Development and Global Health is currently actively recruiting influenza challenge volunteers, advertising compensation of up to $3,500, and possibly more, for participation in a study requiring up to 10 consecutive days away from home and employment.3
Deliberately Infecting Participants
In an influenza challenge study, participants receive a certain dose of live influenza virus intranasally and then remain in a clinical setting while researchers track symptoms, measure how much virus they are shedding, and observe the immune response. NIAID has sponsored these trials known as Controlled Human Infection Model, or CHIM at four Vaccine and Treatment Evaluation Units, the University of Maryland School of Medicine, Saint Louis University, Duke University, and Cincinnati Children’s Hospital Medical Center.4
Challenge studies are conducted in two ways. In model development studies, like the H3N2 study currently underway in Canada, participants receive only the live virus, with no shot given beforehand. The study is designed to establish how the infection progresses, not to test an influenza vaccine. By contrast, in vaccine efficacy challenge studies, participants receive an experimental flu shot first, then are deliberately infected weeks later to see whether the shot prevented or reduced illness.5
The program was championed by the former director of NIAID Anthony Fauci, MD who later came under congressional scrutiny after documents revealed that NIH had funded bat coronavirus research at the Wuhan Institute of Virology through a grant to EcoHealth Alliance.6
Dr. Fauci said:
NIAID investigators have been pioneers in contemporary human influenza challenge trials. These trials provide a powerful tool to study many aspects of influenza disease progression and also can help to efficiently assess new treatments and vaccine candidates.7
Not everyone in the bioethics community agreed. Ruth Macklin, distinguished professor emerita at Albert Einstein College of Medicine and a fellow at the Hastings Center, cut through the efficiency argument by posing the question challenge trials actually raise… “Is it permissible to intentionally inflict serious harm on a few for a possible benefit to many?”8
Community Could Be at Risk
The University of Maryland study confines participants to a clinical facility for up to 10 days after they receive the challenge influenza virus intranasally.9 Whether that period is sufficient to prevent community spread after discharge remains unanswered.
A review of influenza volunteer challenge studies published in the American Journal of Epidemiology analyzed 56 studies involving more than 1,200 participants and found that viral shedding peaked on average around day two after receiving the challenge virus and lasted an average of about five days. More than 30 percent of infected individuals, however, still had detectable infectious virus at five or more days after exposure, and some continued shedding beyond day seven.10
These studies enroll seemingly healthy adults with apparent normal immune function, yet the data shows that the infectious period does not end at the same point for everyone. The studies do not appear to include extended monitoring of participants after their discharge from the clinical facility to determine whether any went on to spread the influenza virus to people in their households or communities.11
The Ethics Debate
Incentives are provided to get willing participants in these types of studies. A survey of 1,500 U.S. adults published in PLoS One found that the two things most likely convince someone to participating in studies like these were (1) understanding the specific risks involved and (2) trusting the institution running the study. Money was also a significant factor. Higher payments consistently attracted people who said they would not have signed up without a financial incentive.12
The University of Maryland is offering up to $3,500 to participate, which is at the high end of what clinical trials typically pay.13 Bioethicists have raised concerns that payments at this level stop functioning as compensation for time and start to function as a reason to accept risks that participants would otherwise decline, with people with low- income populations most at risk of agreeing to volunteer in these risky trials. This raises real bio-ethical concerns.14
Furthermore, no informed consent form can fully account for the risk that the influenza virus they may carry out of the study could spread to an innocent bystander, who never agreed to participate in this risky research.
Viruses Can and Have Escaped the Lab
Keeping live influenza virus in a controlled environment is not a guarantee that it stays there. A peer-reviewed modeling study published in BMC Medicine found that between 5 and 15 percent of accidental escape events involving a transmissible influenza strain would go entirely undetected. That same study catalogued more than fifty accidental human exposures to dangerous pathogens inside research facilities between 1975 and 2016.15
The 1977 influenza pandemic, which infected people worldwide, is believed by researchers to have begun with a Soviet vaccine trial that accidentally reintroduced an influenza strain that had been frozen since the 1950s.16 The SARS-1 virus escaped from laboratories four separate times.17
The influenza strain at the center of the Canada study is a circulating H3N2 variant. Viruses mutate as they replicate inside a living host. What a participant is shedding on day 10 may not be the same strain they were given on day one.18
No Clear Standards or Rules
No binding international standards govern how much risk is acceptable for a healthy volunteer in an infection challenge study. A 2026 stakeholder report published in Biologicals found that researchers, regulators, and ethics review boards cannot agree on what an acceptable risk level even is. They also disagree on what to do if the influenza virus a participant is carrying mutates during the study, and who is legally responsible if someone is seriously harmed.
The report concluded that formal international guidelines are needed before these influenza challenge trials expand any further. Those guidelines do not yet exist.19
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Click here to view References:1 Medical Xpress. Volunteers intentionally exposed to influenza to advance vaccine research. Sept. 2026.
2 National Institutes of Health. Influenza human challenge study begins at NIH-sponsored clinical trial units. Oct. 23, 2019.
3 University of Maryland. Help Us Fight the Flu: Seeking Volunteers 18 to 55. The Elm June 8, 2026.
4 National Institutes of Health. Influenza human challenge study begins at NIH-sponsored clinical trial units. Oct. 23, 2019.
5 ClinicalTrials.gov. Establishing a Controlled Human Infection Model for Influenza H3N2 as a Foundation for Pandemic Preparedness. 2026.
6 U.S. House Committee on Oversight and Government Reform. Scalise, Comer, Jordan Blast Fauci for Awarding EcoHealth Another Grant to Study Bat Coronaviruses. 2023.
7 NIH. Influenza human challenge study begins at NIH-sponsored clinical trial units. Oct. 23, 2019.
8 Macklin R. Human Challenge Studies for Covid-19 Vaccine: Questions about Benefits and Risks. Hastings Center Bioethics Forum June 15, 2020.
9 University of Maryland. Help Us Fight the Flu: Seeking Volunteers 18 to 55. The Elm June 8, 2026.
10 Carrat F, Vergu E, Ferguson NM et al. Time Lines of Infection and Disease in Human Influenza: A Review of Volunteer Challenge Studies. American Journal of Epidemiology 2008.
11 ClinicalTrials.gov. Establishing a Controlled Human Infection Model for Influenza H3N2 as a Foundation for Pandemic Preparedness. 2026.
12 Elsey JWB, Manheim D, Marsh A et al. Ethical acceptability of human challenge trials: Consultation with the US public and with research personnel. PLoS One 2024.
13 University of Maryland. Help Us Fight the Flu: Seeking Volunteers 18 to 55. The Elm June 8, 2026.
14 Elsey JWB, Manheim D, Marsh A et al. Ethical acceptability of human challenge trials: Consultation with the US public and with research personnel. PLoS One 2024.
15 Merler S et al. Containing the accidental laboratory escape of potential pandemic influenza viruses. BMC Medicine 2013.
16 Chen X, Kalyar F, Chughtai AA, MacIntyre CR. Origin of the H1N1 (Russian influenza) pandemic of 1977—A risk assessment using the modified Grunow–Finke tool (mGFT). Risk Analysis 2024.
17 World Health Organization. SARS Risk Assessment and Preparedness Framework. 2004.
18 Medical Xpress. Volunteers intentionally exposed to influenza to advance vaccine research. September 2026.
19 Hoogerwerf MA et al. Refining the regulatory and ethics context of controlled human infection models: a stakeholder meeting report. Biologicals August 2026.
One Response
Won’t it be great if nobody gets sick?
That has been the result of all these kinds of viral transmission studies in the past.
If that occurs, I suspect we will never hear anything about the study again. Bigtime waste of money that coud be put to better use.
Although I also suspect they will put something more nefarious than their fake viruses into the witch’s brew to make sure people do get sick.