RPT-UPDATE 2-CSL says swine flu vaccine protects with one dose

* Study supports single dose vaccine approach

* Could help ease burden of global vaccination

* MedImmune says their H1N1 vaccine ready by end-September (Repeats to additional subscribers) (Updates with CSL quotes on dosage/production and share price)

By Maggie Fox, Health and Science Editor

WASHINGTON, Sept 10 (Reuters) - Australian vaccine maker CSL Ltd (CSL.AX) said on Thursday a single dose of its H1N1 swine flu vaccine would protect adults against the virus, which means vaccine supplies can be stretched further than officials had estimated.

One 15 microgram dose of the CSL vaccine, which does not use an immune booster known as an adjuvant, got the desired immune response in 95 percent of the 240 adults tested, the company reported in the New England Journal of Medicine. "The lower dose offered as good protection as the higher dose," Michael Greenburg, CSL influenza specialist, told reporters in Sydney in a briefing on the development.

The results back reports last week from rival vaccine maker Novartis (NOVN.VX) and China's Sinovac (SVA.A), who separately reported their vaccines got protective immune responses in patients with one dose.

The new H1N1 strain of flu, declared a pandemic on June 11, could eventually infect a third of the world's population, or 2 billion people, according to the World Health Organization.

Because it is a new strain, infectious disease experts have said people would likely need two doses to get full immunity against the virus. They are rushing to put in place vaccine programs as the weather cools in the Northern Hemisphere and the traditional flu season starts.

Other pharmaceutical firms like Sanofi-Aventis (SASY.PA), GlaxoSmithKline (GSK.L) and AstraZeneca's (AZN.L) MedImmune unit are racing to develop H1N1 vaccine as governments scramble to secure supplies.

H1N1 vaccines will be given separately from regular seasonal flu shots, something global health officials admit could create a logistical nightmare. If patients will only need one H1N1 dose, that could ease the burden considerably.

CSL said the single dosage data would not affect its production timetable. CSL has already completed a first batch of 2 million H1N1 vaccine shots and is producing 1-1.5 million doses per week until it fills all orders.

"Because of the demand for this vaccine we will continue producing vaccine as rapidly as we can," said Andrew Cuthbertson, CSL chief scientific officer.

"The positive data means our production will go further in terms of protecting individuals around the world."

CSL has won a $180 million contract from the United States for H1N1 vaccine and an order for 21 million doses for the Australian government. In May it said it expected to book sales of about $250 million from swine flu vaccines in the year to 2010. CSL said that once it had fulfilled its orders, any additional vaccine may be used by the World Health Organisation.

CSL shares last traded, ahead of the single-dose announcement, at A$34.05. The stock has risen by about 11 percent since the virus was declared a pandemic.

For the CSL study, researchers gave two doses of vaccine to all 240 adults, aged 18 to 64.

"Each participant received an initial vaccination followed by a second vaccination three weeks later. The first group received 15 mcg of vaccine, the standard dose used for a single strain in the ... seasonal influenza vaccine, and the second group received 30 mcg of vaccine," CSL said in a statement.

Blood tests showed 96.7 percent of the volunteers who got the 15 mcg dose had an immune repose that has been shown to protect people from flu.

"This immune response remains consistently strong irrespective of age. No deaths, serious adverse events or adverse events of special interest were reported," CSL said.

Separately, MedImmune officials said they had submitted safety data for their nasal spray swine flu vaccine to the U.S. Food and Drug Administration.

"There are no red flags there. We think we can have 5 million doses ready to distribute at the end of September," MedImmune's Dr. Raburn Mallory said in an interview. U.S. officials have not expected vaccination to begin until mid-October.

"Because our vaccine is a live vaccine it tends to have better one-dose efficacy than the killed vaccines," he said. (Additional reporting by Michael Perry in Sydney, Editing by Mark Bendeich)