Moderna will begin its late-stage trial testing a potential vaccine to prevent Covid-19 on July 27, according to a posting published Tuesday on ClinicalTrials.gov. 

The trial will enroll 30,000 participants, according to the website. Participants in the experimental arm will receive a 100 microgram dose of the potential vaccine on the first day and another 29 days later. Some patients will also receive a placebo.

Moderna’s experimental vaccine contains genetic material called messenger RNA, or mRNA. The mRNA is a genetic code that tells cells what to build — in this case, an antigen that may induce an immune response to the virus. It became the first candidate to enter a phase one human trial in March.

In May, the company released data from its early-stage trial, which showed the vaccine produced neutralizing antibodies against Covid-19 in at least eight participants. The vaccine also produced binding antibodies in all participants.

The effort by Moderna is one of several working on a potential vaccine for Covid-19, which has infected more than 13 million people and killed at least 573,200 as of Tuesday, according to data compiled by Johns Hopkins University.  More than 100 vaccines are under development globally, according to the World Health Organization.

Earlier this month, pharmaceutical giant Pfizer released positive results from its closely watched early-stage human trial of a coronavirus vaccine.

This is a developing story. Please check back for updates.