The French firm announced the initiation of the Phase II trials earlier today, following on from Phase I studies started in September last year.

The vaccine is based on Dutch firm Crucell's popular PER.C6 cell line, which has proved promising in terms of developing an effective cell based vaccine that can be manufactured on a commercial scale.

The cell culture flu vaccine project is part of a five year $97m contract with the HHS awarded back in 2005. The deal fired up Sanofi Pasteur's cell-based flu vaccine programme and brought the project towards the centre of the company's development plans.

With plans pushing on, a recent R&D update by parent company Sanofi Aventis had regulatory submission for the vaccine scheduled for 2010.

This fits squarely in with the five year timescale of the HHS contract, which comprised three main development branches for Sanofi to pursue: acceleration of cell-based flu vaccine plans (with Phase III trials to be underway by the end of 2008); creation and design of a manufacturing process to produce the vaccine in large quantities; and preparation of a feasibility plan to establish a cell culture vaccine production facility.

Crucell's PER.C6 cell line has helped the company fulfil two of these criteria, with the production scale potential of the cell line demonstrated in a successful bioreactor run of 20,000 litres, showing its potential for commercial scale manufacturing of the flu shot.

Sanofi used the services of the biologics arm of Swiss firm Lonza to achieve the scale-up process for the vaccine.

The US-based facility for which Sanofi will present a feasibility study will be designed to supply 300 million doses of monovalent flu vaccine annually.

While Sanofi is forging ahead with its cell culture-based flu shot, it will not be first to the market with a flu vaccine making use of cell culture based techniques.

Back in June, for example, Swiss firm Novartis was granted EU approval of its cell-based seasonal flu jab, Optaflu.

The vaccine should be available in Germany and Austria for this year's flu season, and remaining EU countries in time for next year. US submission is anticipated during 2008.

Cell culture production methods are currently the hot topic in vaccine manufacture, eliminating as they do some of the cumbersome impracticalities of traditional egg-based production techniques.

Key benefits of the approach include much faster production, removal of the need to rely on the availability of suitable eggs, and quicker response times in the event of a pandemic.

Both Novartis and Sanofi Pasteur are also in the process of developing cell-based vaccines against various strains of avian flu.