Moderna Inc. shares fell after Merck & Co. said it sold its stake in the biotechnology company that’s in the midst of developing a COVID-19 vaccine.

Merck sold its direct equity investment in Moderna during the first half of the fourth quarter, according to a statement from the U.S. drugmaker on Wednesday. No terms of the sale of the holdings were given.

Shares of Moderna fell four per cent in trading before the U.S. market opened, a modest pullback following the stock’s more-than-sevenfold surge so far this year. Based in Cambridge, Massachusetts, Moderna is developing one of the fastest-moving potential coronavirus vaccines.

The shot is slated for review by U.S. regulators in the coming weeks.

Merck was an early investor in Moderna, which sold shares to the public for the first time in Dec. 2018. The U.S. drug giant said it had seen a large increase in the value of its investment since it first put money into the company in 2015.

“Merck achieved a substantial gain on its direct holding in MRNA over the life of the investment, particularly in 2020 given the substantial appreciation in MRNA’s stock price,” the drugmaker said in its statement.

Merck still holds an indirect exposure to Moderna through its investment in venture funds, the company said, and the drugmakers are working together on developing new cancer therapies.