CNN reported on Monday that the first Phase 3 clinical trial of a COVID-19 vaccine in the US began on 27 July 2020.

The investigational vaccine was developed by biotechnology company Moderna and the National Institute of Allergy and Infectious Diseases, part of the National Institutes of Health.

This trial is to be conducted at nearly 100 US research sites, according to Moderna. The first patient was dosed at a site in Savannah, Georgia.

The trial is expected to enroll about 30,000 adult volunteers. It will evaluate the safety of the Moderna/NIH vaccine and whether it can prevent symptomatic COVID-19 after two doses, among other outcomes.

Volunteers will receive either two 100 microgram injections of the vaccine or a placebo about 28 days apart. Investigators and participants will not know who has received the vaccine.

According to CNN, results from a phase 1 trial of the vaccine published earlier in July 2020 in the New England Journal of Medicine found it induced immune responses in all of the volunteers and was generally safe. It had mild side effects, including fatigue, chills, headache, muscle pain and pain at the injection site.

According to the US Centres for Disease Control and Prevention, a Phase 1 study typically studies a small number of people and focuses on whether a vaccine is safe and elicits an immune response. In Phase 2, the clinical study is expanded and the vaccine is given to people who have characteristics, such as age and physical health, similar to those for whom the new vaccine is intended,

In Phase 3, the vaccine is given to thousands of people and tested for efficacy and again for safety.

The Moderna/NIH vaccine is one of 25 in clinical trials around the world, according to the World Health Organisation.