A Massachusetts company says its experimental vaccine against the coronavirus showed encouraging results in very early testing.

Cambridge-based Moderna Inc. said Monday that its vaccine triggered immune responses in eight healthy, middle-aged volunteers.

The experimental vaccine generated antibodies similar to those seen in people who have recovered from COVID-19 in study volunteers who were given either a low or medium dose.

The study is being led by the U.S. National Institutes of Health.

In the next phase, researchers will try to determine which dose is best for a definitive experiment that they aim to start in July.

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