By Jenny Strasburg

LONDON -- AstraZeneca PLC said it agreed to buy Boston-based Alexion Pharmaceuticals Inc. for $39 billion in cash and stock, a move that would bolster the British drug giant's footprint in immunology and rare diseases.

The deal comes at a pivotal time for AstraZeneca, which is in late-stage development of a leading Covid-19 vaccine developed in partnership with the University of Oxford. The vaccine is being reviewed by U.K. and European medicines regulators, and could be authorized for emergency use in the U.K. within weeks, scientists involved in it have said.

The company has embarked on one of the most ambitious efforts to manufacture and distribute the vaccine among a handful of Western pharmaceutical giants, assuming it gets the green light for its shot. With the Alexion deal, it is now also pursuing one of the biggest drug-industry deals of the year.

AstraZeneca said Alexion will give it a greater scientific presence in immunology, with a rare-disease unit based in Boston. Directors of both companies have approved the acquisition, which they expect to close in the third quarter of 2021.

AstraZeneca has reinvented itself in recent years as a cancer-drug powerhouse. It had suffered years of shrinking revenue as blockbusters in its portfolio were hit by generic competition when patents expired.

AstraZeneca's said its cash-and-stock agreement amounts to $175 per Alexion share, based on the one-month average value of AstraZeneca's U.S.-traded American depositary receipts. The offer is split between $60 in cash and 2.1243 American depositary shares. That represents a 40% premium over Alexion's one-month share-price average, AstraZeneca said. Alexion's shares closed Friday at $120.98.

The companies have been talking for several months, said AstraZeneca Chief Executive Pascal Soriot. Mr. Soriot said that the disruption should be minimal for AstraZeneca's work rolling out a global Covid-19 vaccine, adding that for a deal this attractive, "You do it when the opportunity arises."

He and AstraZeneca's chief financial officer, Marc Dunoyer, told reporters on a call Saturday that AstraZeneca and Alexion don't overlap a great deal geographically, and Alexion's roughly 3,000 employees will be fairly simple to integrate.

AstraZeneca expects to have regulatory approvals by the third quarter, possibly sooner, by which time they will be well into the vaccine rollout, the executives said. "Our belief is that by Q3 the world won't have returned to total normalcy, but close enough," Mr. Soriot said.

(More to come)

Write to Jenny Strasburg at jenny.strasburg@wsj.com

(END) Dow Jones Newswires

12-12-20 0925ET