Pfizer (PFE.US) is seeking to sell its remaining stake in COVID-19 vaccine partner BioNTech SE (BNTX.US), signaling the gradual winding down of one of the most profitable collaborations during the pandemic. According to sources familiar with the matter, Pfizer intends to offload approximately 4.55 million American Depositary Receipts (ADRs) in an overnight block trade, priced between $108 and $111.70 per share. At the upper end of the range, the sale would generate around $508 million in proceeds for Pfizer.

The two companies joined forces in 2020 to develop a COVID-19 vaccine, which generated tens of billions in global revenue and secured supply agreements with governments in the U.S. and the European Union during the peak of the pandemic. Pfizer's equity investment in BioNTech was part of their collaborative agreement. The firms continue to work together on COVID-19 vaccine formulations using BioNTech's proprietary mRNA technology, sharing profits from the venture.

Meanwhile, Pfizer recently concluded a fierce bidding war to acquire obesity drug startup Metsera Inc. for $10 billion, partly to offset declining COVID-related revenue with blockbuster weight-loss treatments. As the pandemic recedes, BioNTech has refocused on its original mission of cancer therapeutics, leveraging accumulated capital to advance research. The company has also entered a collaboration with Bristol Myers Squibb worth up to $11.1 billion.