Pharmaceutical company PowderJect is to increase production of its flu vaccine following the unexpected decision by its US rival Wyeth to withdraw from the flu market.

PowderJect, which is being stalked by a US predator, saw its shares rise again following the news. Shares had already risen 60 per cent following an informal takeover bid.

PowderJect, based at Oxford Science Park, has already increased capacity at its Merseyside factory to more than 27 million doses this season.

The company wants to increase this to 35 million doses next year and 45 million the following year. It will speed up investment to ensure the USA has adequate vaccine supplies.

Chief executive Paul Drayson said: "We think it particularly important to reassure our customers that we will do everything we can to ensure they will receive adequate supplies in the next flu season.

"The demand for flu vaccine is growing rapidly as both consumers and governments recognise the health and economic benefits of immunisation."

Wyeth is the US number three flu vaccine supplier, with estimated £50m annual sales.

PowderJect, the number two, has projected sales of £95m.