SARS-CoV-2 Delta variant dose finding infection study
Researchers at Imperial College London are running a study to see how the immune system responds to the COVID-19 Delta variant. In this type of trial, known as a human challenge study, healthy vaccinated adults aged 18 to 30 are deliberately given a very small, carefully measured dose of the virus. Participants will stay in a private quarantine room at Chelsea and Westminster Hospital for around two weeks. Doctors and nurses will monitor them around the clock to track their symptoms and immune responses. The main goal is to find the smallest dose needed to study the virus safely, causing only mild or no symptoms. Finding this safe dose will help researchers test new COVID-19 vaccines and antiviral medicines much faster in future trials. Participants receive payment for their time and are monitored for one year.
At a glance
What is this study about?
This clinical trial is called a 'human challenge' study. Instead of waiting for people to catch COVID-19 naturally in the community, researchers give healthy, fully vaccinated volunteers a tiny, controlled dose of the SARS-CoV-2 Delta variant drops into the nose. This lets scientists watch exactly how the body and immune system react from the very first moment of exposure.
The main goal is to find the lowest possible dose that causes a mild or symptom-free infection in vaccinated people. In standard clinical trials, testing new vaccines or medicines can take years and require tens of thousands of participants. By establishing a safe challenge model, scientists can quickly test new booster jabs and antiviral medicines on much smaller groups of people.
Safety is the top priority throughout the trial. The study takes place in a dedicated hospital isolation unit with medical staff available day and night. Participants are screened thoroughly before joining, and doctors have effective antiviral medicines ready to treat anyone who shows signs of a more severe illness.
Key takeaways
- Tests how vaccinated adults aged 18–30 respond to a small dose of the Delta COVID-19 variant.
- Requires a two-week stay in a specialist hospital quarantine unit in London.
- Follow-up checks continue for up to one year after the stay.
- Participants receive compensation for their time, travel, and commitment.
- Aims to make developing future COVID-19 vaccines and treatments faster and more effective.
Who may be eligible?
This study is open to healthy young adults aged between 18 and 30 who have already completed a full course of an approved COVID-19 vaccine. Your last dose must have been given at least 14 days before joining the study. You will also have a blood test to check your antibody levels before you can be accepted.
To keep risks as low as possible, volunteers must be in very good health with no ongoing medical conditions. The study team will review your medical history and carry out health checks, including blood tests, a heart tracing (ECG), and a chest X-ray.
Both men and women taking part must agree to use effective contraception throughout the study and for six months afterwards. Women must not be pregnant or breastfeeding, and regular pregnancy tests will be carried out before the study begins.
Could this study suit you?
Answer these quick questions to see if you may be eligible. This is a guide only — the research team makes the final call.
- I am between 18 and 30 years old.
- I have had a full course of an approved COVID-19 vaccine.
- My last vaccine dose was at least 14 days ago.
- I am in good general health with no significant long-term illnesses.
- I am willing to stay in hospital quarantine for around two weeks.
- I am willing to use reliable contraception during and after the study.
What does participation involve?
Taking part lasts for about one year in total. First, you will attend screening visits at Imperial College Healthcare NHS Trust to make sure the trial is safe for you. If eligible, you will be admitted to an isolation room at Chelsea and Westminster Hospital for approximately two weeks. During this stay, you will receive the virus drops in your nose and have regular tests, including daily nose and throat swabs, blood samples, and checks of your temperature and oxygen levels. Highly trained doctors and nurses will monitor you 24 hours a day. After leaving the hospital unit, you will return for several outpatient check-ups over the course of 12 months to ensure you have fully recovered.
Potential risks and benefits
Locations (3)
- NIHR Imperial Clinical Research FacilityCity onlyLondon, England
- Chelsea and Westminster HospitalApproximateLondon, England
- Oxford Experimental Medicine Clinical Research FacilityCity onlyOxford, England
Common questions
What is a 'human challenge' study?
It is a trial where healthy volunteers are carefully given a small, measured dose of an infection in a safe hospital environment. This allows doctors to study the illness and test treatments under strict supervision.
Will I get very sick from the virus?
The study aims to use a dose that causes either no symptoms or only mild, cold-like symptoms. Because volunteers are young, vaccinated, and thoroughly checked, the risk of severe illness is low.
Will I be paid for taking part?
Yes. Volunteers receive financial compensation to cover the time, stay in quarantine, and travel required for the trial.
What is the quarantine stay like?
You will stay in an en-suite hospital room with Wi-Fi, television, and meals provided. You cannot leave the room during the quarantine period to prevent spreading the virus to others.
Can I leave the study early if I change my mind?
Yes, taking part is entirely voluntary. However, if you have already received the virus, you would need to stay isolated until tests show you are no longer contagious, to protect the public.
How to find out more
Polly Fox
Always speak to your GP or specialist before deciding to take part in a study.
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