Further information and resources

The UK’s experience and expertise in human challenge trials as well as in wider COVID-19 science will help us tackle the pandemic, benefiting people in the UK and worldwide. Professor Chris Chiu Chief Investigator, Imperial College London

The SARS-CoV-2 coronavirus is likely to cause outbreaks of COVID-19 in the UK and around the world for years to come, even with the current vaccines available. There is still an urgent need to better understand the infection and continue efforts to develop new vaccines and treatments against emerging strains of the virus.

Human infection studies can help to address this need. This kind of study can provide an efficient platform for rapidly testing new vaccines and treatments. Human infection studies can also give researchers very detailed information about the infection, some of which can only be found in this way and will have important public health benefits.

Vaccines and treatments

Even though there are COVID-19 vaccines are available, there are good reasons why we need continued research into new vaccines and treatments for COVID-19. 

It will take a long time to vaccinate everyone around the world. New vaccines will increase availability, especially if they do not require cold storage (and therefore can be used in more remote places or countries without the infrastructure to keep them cold). 

The virus is changing, so we will likely need to keep updating the vaccines and testing them against new emerging variants of the coronavirus.

Having ‘single shot’ vaccines (highly effective after a single dose) would mean we could protect the population faster. Furthermore, finding new ways to deliver vaccines (for example, via a nasal spray) could also be beneficial by making them easier to administer and more acceptable. 

Some people won’t respond to the current vaccines or can’t be given them for medical reasons (or don’t want a vaccine). We still need better treatments for this group of people to help prevent them from being infected, or from becoming seriously ill or dying from COVID-19.

Human infection studies will also be able to help answer fundamental questions about vaccines, including whether they stop people passing on the virus as well as preventing them from becoming seriously unwell. If vaccines can block transmission too, they will be more effective because they create herd immunity and protect those who aren’t vaccinated (including vulnerable groups who may be unable to receive a vaccine). This kind of study could also help determine the best timing of second doses and boosters, and to understand how long immunity from the vaccines last. 

Understanding COVID-19 and the immune response to the virus

There are many aspects of SARS-CoV-2 infection that scientists still don’t understand that human infection studies could help answer. Because volunteers taking part in such a study can be monitored from the moment they are given the virus, researchers can get very detailed information about the infection which wouldn’t be possible from people who have caught it naturally.

A human infection study can provide critical insights including:

• Underlying factors of why some people get infected and why others don’t, or why some people have symptoms or worse symptoms than those who don’t experience any symptoms.
• The incubation period of COVID-19 (the time from a person catching the virus to when they start to feel unwell), during which people can be infectious.
• The overall length of time that people are infectious (from first being exposed to when the virus is no longer detectable) and the best tests to identify infectious people.
• The risk of reinfection (some people have caught COVID-19 more than once). Researchers can use this kind of study to find out how long natural immunity lasts, factors that put people at higher risk of reinfection, whether new variants pose a higher risk of reinfection, and if reinfected people can spread the virus to others.
• Why many people infected with coronavirus have no symptoms (asymptomatic) but are still major spreaders of the infection.

Understanding more about the infection will help to inform public health measures like self-isolation and travel quarantine periods, track and trace efforts, how to reduce asymptomatic spread and community testing programmes.

No clinical study is completely risk-free, but the researchers who designed the human infection studies have done everything possible to minimise the risks to the volunteers who take part, the study staff, and wider society. The team have also ensured that potential volunteers are fully informed about the risks before agreeing to take part.

The volunteers allowed to join the study are at the lowest risk of becoming severely unwell with COVID-19; they are young (18-30 years old), vaccinated against COVID-19 and in good health. During the study, they might get common symptoms of COVID-19 (including fever, tiredness, a cough, and changes to taste/smell), but these are expected to be mild and of short duration (1-2 weeks).

There is a small risk of the volunteers getting long COVID, with more prolonged symptoms that can last for months. Some of the common symptoms reported are loss of smell/taste, tiredness and brain fog. Volunteers will be monitored for a year after being exposed to the virus, and if anyone develops long COVID they will be supported (both in terms of care via specialist clinics and compensation for loss of earnings). 

Severe disease or death due to COVID-19 in young people is very uncommon, but there is still a small risk. However, the risk of the volunteers in the study becoming seriously unwell or dying is relatively lower, because they are screened for underlying health conditions and other factors that increase the chances of severe disease. 

There are also other measures in place during the study to minimise these risks, including giving the volunteers the smallest amount of virus needed for infection and constantly monitoring them for early signs of more serious symptoms. 

If any of the volunteers show any concerning symptoms, they will be moved from the quarantine unit where the study is taking place into the main Chelsea and Westminster Hospital, which has an excellent infectious diseases and critical care team who would take over their care. The study is fully insured should any volunteer experience any serious consequences.

A specialist human challenge independent research ethics committee has been convened to review these types of studies. Review by an ethics committee is one of a series of safeguards intended to protect people taking part in all clinical research studies. It is a thorough process and there are many principles that are considered during the review, including weighing up the benefits against the risks. Another important consideration is making sure the potential participants receive high-quality, comprehensive information about the study in a timely fashion. The information about the human infection study sent to and discussed with potential volunteers is very detailed and there are measures in place to make sure it is understood, so potential volunteers have a full picture of what the risks are and what the study entails before agreeing to take part (this is known as informed consent).

This study received ethical approval to commence on 7 September 2022. 

The first human infection study with coronavirus received ethical approval in February 2021.

You can find out more about Research Ethics Committees (RECs) and the Health Research Authority (HRA) approvals on the HRA website. A REC is made up of experts from different backgrounds (for example doctors, clinical trial experts, and scientists) and members of the public.

If you are interested in the general principles underpinning ethical review, you might find this website created by a research ethics advisor of interest.