Moderna is testing a new version of its vaccine.
The updated vaccine is easier to distribute because it can remain stable in refrigerators.
The below-freezing temperature required by the company's current shot makes it more complicated to get to vaccine sites.
Moderna says it hopes the new vaccine can be given as a single dose.
Its current vaccine requires a booster shot four weeks after the first.
The new trials are in the early stages.
Moderna says it will also conduct trials in the future to determine if its new vaccine can be used as a booster.
Pfizer and Johnson & Johnson have also said they will test new versions of their vaccines to see if they can be used as boosters to protect against new coronavirus variants.
