The company said it has enrolled 21,411 participants in the study so far. It had 17,000 participants as of last week, with 24% from communities of color.
The talks closely follow similar discussions with the European Union to supply its vaccine candidate mRNA-1273.
Moderna said the immune responses in those aged between 56 and 70 years, above 70 and those in the age-group of 18 and 55 were similar.
"We are scaling up our manufacturing capacity to address the global health crisis with a vaccine that is widely available once approved for use."
CEO Stéphane Bancel has also cashed out on shares in recent months.
Drugmakers say they first need to make sure the vaccines are safe and effective more generally.
It appeared to be an improvement over results of AstraZeneca's COVID-19 vaccine in a similar study.
The federal government is supporting Moderna's vaccine project with nearly a billion dollars and has chosen it as one of the first to enter large-scale human trials.
The answer to this is more complicated than one might think and centers around the question of the strength and longevity of the immune response.
The clinical stage biotechnology company has said its development of a vaccine for COVID-19 will not be affected.