An experimental COVID-19 vaccine tested on humans is among the first to show promising results. Moderna, the biotech company behind the vaccine, launched the clinical trial in March along with Kaiser Permanente Washington Health Research Institute. 

Moderna's Phase 1 trial generated promising immune responses in all 45 healthy volunteers. The volunteers received two doses of the candidate vaccine and were later found to have high levels of antibodies critical to fight off the disease, exceeding the average levels observed in people who had recovered from COVID-19. 

The research team described the clinical trial in the journal New England Journal of Medicine, saying that it's a huge step in the right direction. 

"This is very exciting," said Dr. John with Kaiser Permanente. "Everyone should feel encouraged. There are no serious safety concerns. And individuals do produce antibodies that are capable of neutralizing the virus."

Researchers said that the experimental virus is essential for building immunity and a sign that the vaccine offers some protection against the coronavirus.

Moderna in April continued the Phase 1 clinical trial and added adults over the age of 55 -- a group considered to have a higher risk of getting the virus -- aiming to enroll 120 test patients. According to the company, the volunteers will be monitored for a year in order to check how long immunity lasts and to look for side effects. In May, Moderna began Phase 2 of the trial. It plans to start the third phase on July 27. 

Moderna's Phase 1 has a goal of ensuring safe treatment and also to determine the most effective dose to prevent acquiring the virus. For Phase 2, the company tested the vaccine in a much bigger group and got an early read on the drug's effectiveness. Phase 3 will be performed in an even larger group in order to confirm if the drug works and also to identify any rare side effects. The firm is looking to add approximately 30,000 test patients for its third phase. 

Volunteers will either get a placebo or the vaccine. They will be monitored for two years to check for adverse reactions and to see whether they get infected with the coronavirus. The team said the most common side effects noted so far were weakness, headache, chills, and fatigue. 

The U.S. government has pledged nearly half a billion dollars for Moderna's experimental vaccine. It was one of the firms chosen to enter large-scale trials on humans. A successful vaccine could be a turning point for the company, which has never had a licensed product.