The roles are to be cut as Pfizer is discontinuing its pharmaceutical sciences small molecule (PSSM) operations at Sandwich in Kent, the company confirmed to Sky News.

It's part of a company-wide cost-cutting program, Pfizer said, as it aims to bring down spending due to lower than expected sales of its COVID-19 vaccines and treatment.

Affected staff were notified in a brief announcement on Tuesday morning and employee redundancy consultation will take place over the coming 45 days, according to a Pfizer staff member who worked in the PSSM unit.

Staff will attend work and are expected to be given notice of their exit date in January, Sky News understands.

Of the 500 job losses most are scientist roles though administrative roles are also being lost as the PSSM unit makes medicine for clinical trials and helps scale up production of new drugs.

It's understood the roles will be moved to other PSSM sites in Chennai, India and Connecticut, the United States and staff being made redundant at the Sandwich site will work to transition projects to those locations.

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Neither vaccines nor COVID-19 drugs such as Paxlovid are being worked on by the discontinued Sandwich operation. Mostly tablets and some intravenous drugs are worked on there, the Pfizer staff member told Sky.

The majority of staff were surprised at the announcement, the staff member said.

While job cuts were expected they thought 20% to 30% of the unit could be culled, rather than the entire PSSM operation in Sandwich.

"Various areas of Pfizer's global enterprise are making changes to operate more efficiently and effectively," a Pfizer spokesperson said.

"These changes will be implemented on a rolling basis and will differ area to area."

"More information around this global program will be shared over the coming months and as part of the full year guidance for 2024," Pfizer added.

Last month Pfizer cut its revenue forecast by 13% and announced $3.5bn (£2.8bn) of cuts to jobs and expenses.

In previous years, however, record revenue was reported thanks to its development of a COVID-19 vaccine with German biotech company BioNTech.