Drugmaker Novartis AG said on Thursday a single dose of its swine flu vaccine might protect against the virus, boosting hopes that potentially tight supplies could go further when mass immunization starts this month.

The new H1N1 strain of flu, declared a pandemic on June 11, could eventually infect 2 billion people, according to World Health Organization (WHO) estimates.

Because it is a new strain, most infectious disease experts say people will need two doses to get full immunity against the virus. They are rushing vaccine programs ahead of a possible second wave of cases in the traditional northern hemisphere winter flu season.

Vaccination is expected to get under way in some countries this month with many others starting in October.

Novartis said its Celtura H1N1 vaccine gave people a strong immune response after just one dose in a pilot trial, and Chinese health authorities gave a green light to Sinovac, which says its vaccine also needs only one shot to be effective.

This is good news as one dose of Celtura may be sufficient to protect adults against the swine flu. This potentially boosts that availability of flu vaccines for the upcoming flu season when a large outbreak of swing flu is expected, said Karl-Heinz Koch, an analyst at Swiss brokerage Helvea.

Another key variable is vaccine yield in the manufacturing process. Yields were initially low but the WHO said last month they were improving and one strain seemed to be yielding the same amount as seasonal vaccine.

Cell-based vaccines like Novartis's are quicker and easier to manufacture than traditional flu vaccines, which are grown in chicken eggs. However, supplies are limited for now -- they currently make up about 30 percent of the Swiss group's capacity.

Novartis said a pilot trial of Celtura run by Britain's Leicester University with 100 volunteers showed a potentially protective immune response in 80 percent of the subjects after one dose and more than 90 percent after two doses. Other studies with more than 6,000 adults and children are continuing.

Sinovac, the first company to complete clinical trials, received approval from Chinese health authorities to mass produce a vaccine for the new strain of H1N1 and raised its annual sales forecast. Some experts remain skeptical, as Sinovac has not published data to back up its claims.

Sinovac shares rose some 16 percent to $9.90 by 1351 GMT, while Novartis slipped 0.8 percent to 48.62 Swiss francs, in line with the DJ Stoxx European healthcare sector.

WINDFALLS

Other pharmaceutical companies like Sanofi Aventis, GlaxoSmithKline and AstraZeneca's MedImmune unit are also racing to develop H1N1 vaccine as governments scramble to secure supplies.

Clinical trials to see what kind of dose will be needed are under way in the United States, Australia and Europe.

Australia's CSL is already producing H1N1 vaccine and is making 1.0 million to 1.5 million doses per week until it fills all orders.

Antiviral drugs which treat flu rather than immunize -- Glaxo's Relenza and Tamiflu, made by Switzerland's Roche -- are also in high demand.

Sales to governments will provide a revenue and profit windfall for many drugmakers this year and in 2010.

At the beginning of this year, we forecast our sales would rise by 20 percent, Sinovac Chief Executive Yin Weidong said on Thursday. Looking at things now, H1N1has given us an opportunity, so the rise should be more than 20 percent.

H1N1 vaccines would be given separately from regular seasonal flu shots.

Vaccines arrived too late in the 1957 and 1968 flu pandemics to be of much use, and flu vaccines had not been developed in the 1918 Spanish flu pandemic which killed an estimated 50 million people.

Medicine