Initial doses have been shipped to the US National Institutes of Health for a clinical study.
The new vaccine, called mRNA-1273.351, will be evaluated as a booster shot for people who have already been vaccinated against coronavirus and as a primary vaccine for people who haven't had coronavirus and have yet to be vaccinated.
Moderna said it will also evaluate a "multivalent" booster shot that combines the new vaccine formulation with the current vaccine.
Additionally, the company said it has begun to test whether a third, lower dose of its current Covid-19 vaccine can increase immunity against coronavirus variants of concern, with some study participants already getting third doses.