John Brown, the quietly-spoken Scot who transformed Acambis from a loss-making biotech into a profitable vaccines company, is to step down as chief executive as soon as a successor is found.
His departure comes as a blow to the company and sent Acambis shares down 8 per cent yesterday. Observers said the change in management added to the uncertainty which already exists over how the company's profits can be sustained when it has completed a giant contract to supply smallpox vaccine to the US government.
Dr Brown said he was quitting to spend more time with his wife and two teenage sons in Edinburgh. Acambis is based in Cambridge and the smallpox contract has required regular trips to the US.
He said: "I want to spend more nights at home than I do away, and I have not managed that in the last couple of years. I am proud of what we have achieved at Acambis. We created a really good team and we made it a profitable biotech company. There are not that many in Europe."
Dr Brown joined Acambis, then called Peptide Therapeutics, as finance director nine years ago and was made chief executive in 1997.
He is already chairman of the Roslin Institute, near Edinburgh, which cloned Dolly the sheep and said he would be looking for a new commercial role with growing companies. "There is some terrific science in Scotland and I want to be involved in creating more value from it."
The Acambis board will appoint headhunters to conduct the search for a new chief executive. The current finance director, Gordon Cameron, is expected to be the strongest internal candidate. Fund managers said the job is also likely to attract considerable interest from senior directors of some US biotechs.
Dr Brown's final set of results - for the six months to 30 June - revealed Acambis made profits of £20.6m, compared to a £6.1m loss for the same period last year. The company has now made all 155 million doses of smallpox vaccine which will be used as the US government's stockpile against a bioterrorist attack.
There was no news on further contracts with other governments, however, or on the terms of a likely contract to maintain the US stockpile. Analysts had hoped for some progress to make sure the company will not slip back into the red before Acambis can launch its more ambitious vaccines against the West Nile virus and yellow fever.
US regulators have requested more details from Acambis on the West Nile vaccine before agreeing to meet the company, which could delay its launch, analysts said.