A clinical trial is when treatments or interventions are tested on a sample of people. This assesses safety and effectiveness, and any side effects of the treatment are noted, from the mildest to the most serious. Effectiveness is compared against other interventions or existing products. It is a crucial part of research that, if proven safe and effective, allows new treatments to be safely rolled out on a large scale. It’s a legal requirement, too.
Clinical trials are carefully planned by a team of researchers who usually include scientists, healthcare professionals and doctors. These plans, and the trial itself, has to be approved before it can begin. The medical regulation and approval process for a clinical trial is different in each country. Regulators make a decision by weighing the risks and benefits of all factors of any proposed trial. Approval of the trial doesn't mean the treatment is safe, only that the trial is safe and reasonable to proceed with the next stage. Computer modelling or laboratory tests may have formed the basis of any clinical trial design. Research on animals usually precedes research on human volunteers. After approval of the trial, the treatment or intervention is tested on a small number of people in the early phases. This is typically a fit and healthy set of people so that any unwanted effects can have the least serious consequences. Consent is a really important concept here – those running the trial need to share as much information as possible with what they know or predict to happen to the participants volunteering, and any potentially unwanted or serious effects (adverse events). The trial participants will need to sign consent forms to say they have had risks explained to them and understand them. If that phase is successful it undergoes further phases of testing which include a larger and more diverse group of people. This might include those classed as more vulnerable, such as children or the elderly, or with a particular medical condition. At each point, the volunteers of the trial are carefully monitored throughout the process for any side effects and the effectiveness of the treatment or intervention.
After completion of the trial, the data will be put together and presented to the medical regulator in that country to seek approval for the treatment to be made available to the general population. Legally, all medicines or medical interventions need to have regulatory approval. In the UK, the MHRA (Medicines and Healthcare products Regulatory Agency) performs this role. All approved vaccines, including each brand of COVID-19 vaccine, have gone through all these stages of the clinical trials, so they have been thoroughly tested as safe and effective for use.
Anyone can volunteer for a clinical trial. Some may pay you, others won't, and some may offer to pay travel expenses. Any trial will have a strict set of criteria - age, gender, no medical conditions, or you may need to have a particular condition - and you either fit this or you don't. You'll also have to find out about what it involves in terms of your time commitment (per appointment and number of appointments, and where appointments are based) and any interventions that may be invasive. You are free to decide at any point if it's unacceptable and you do not wish to proceed further, including once you've started the trial. They will likely request your doctor's details to check on any other medical conditions, and let your doctor know that you're participating.