Skepticism may have greeted AstraZeneca’s willingness to pay more than $15 billion for MedImmune. But no one is questioning Carl Icahn’s judgement. The 71-year-old, who Forbes estimates is worth $13 billion, is netting at least $300 million in gains for his hedge fund from the pending sale.

The deal came after Icahn, who just this year built up a stake of more than 10 million shares in the vaccine maker, told the company that he planned to run a proxy campaign to get a new board slate if it did not agree to seek a buyer. “This proves again that activism does work to enhance value for all shareholders,” says Icahn, adding that supports the transaction.

In an interview with Reuters, Ichan declined to discuss his stock gains for MedImmune, which surged 18 percent on Nasdaq on Monday. Icahn credited Alex Denner, a former Morgan Stanley biotech fund manager and PhD who now works for Icahn’s hedge fund, for finding the investment.

A person familiar with the matter said Icahn roughly doubled the value of his MedImmune investment, buying into the stock when it was around $30 a share a few months ago.

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