Sept. 11 (Bloomberg) -- A single shot of swine flu vaccine protected healthy adults within eight to 10 days, according to a U.S. study that doubles anticipated stockpiles and may help people get immunized faster.

The findings, the first from U.S.-sponsored clinical trials, were presented today. They bolster similar results published by Melbourne-based CSL Ltd., said Anthony Fauci, director of the National Institute of Allergy and Infectious Disease in Bethesda, Maryland, in an interview. The CSL study found that more than 95 percent of 240 patients who were given a single shot had protective antibodies three weeks later.

World health officials had anticipated that two shots would be required, three weeks apart, because people were being exposed to the new virus for the first time. Critics said a multi-dose regime wouldn’t come in time to slow the widespread outbreaks already triggered this month by the start of U.S. schools. Shots also may be available in time to bring relief in the Southern Hemisphere, where swine flu recently peaked.

“It’s good news because the vaccine is inducing a powerful immune response,” Fauci said of the U.S. results. “The standard time is 21 days, but we drew blood just to get a head start on seeing what was happening, and we found that at 8 to 10 days we got a robust response.”

Spreading Quickly

Swine flu, also known as H1N1, has become the world’s fastest-moving influenza pandemic, sweeping across 177 countries in the four months since it was first identified, according to the U.S. Centers for Disease Control and Prevention based in Atlanta. More than 1 million people have already contracted the virus in New York alone, according to estimates by the city’s health department.

“We’re very encouraged by the data,” Kathleen Sebelius, secretary of the U.S. Department of Health and Human Services, said today at a briefing with reporters. “Americans who get their H1N1 vaccine will most likely be immunized and protected against the virus sooner than we thought.”

Five U.S.-sponsored trials were initiated July 22 to test safety and proper dosing of a pandemic vaccine. The results of the first U.S. study and that conducted by CSL suggest one dose of the formula used by drugmakers should offer H1N1 protection similar to the seasonal flu shot. Paris-based Sanofi Aventis SA, London-based GlaxoSmithKline Plc, and Basel, Switzerland-based Novartis AG are among the other companies making the vaccine.

Consistent Data

“This vaccine could substantially reduce the spread and impact of the pandemic virus,” Anne Kelso, director of the World Health Organization’s collaborating center in Melbourne, said today in an e-mail. “The data are also consistent with the trial results recently reported by China for a similar type of vaccine, so we can be hopeful that many countries will have access to effective pandemic vaccines over the coming months.”

CSL’s study, published yesterday by the New England Journal of Medicine, found that 21 days after a first shot was given, more than 95 percent of the 240 patients had levels of protective antibodies sufficient to fight off the flu.

The shot contained 15 micrograms of antigen, the same level as for seasonal flu vaccines. It had similar side effects to regular flu shots, the most common being headache and pain at the injection site, CSL said.

“I’ve heard it referred to as jaw-dropping,” said Paul Perreault, president of CSL Biotherapies, CSL’s vaccine unit, in a telephone interview yesterday. “It’s pretty similar to the seasonal vaccine, which is very good news. There’s enough data here to indicate that it’s probably going to be one dose.”

CSL rose 16 cents, or less than 1 percent, to A$34.15 today at the close of Sydney trading.

Australia, U.S. Orders

The company is producing about 19 percent of the U.S. stockpile and is Australia’s sole supplier of pandemic shot, called Panvax H1N1. CSL has agreed to provide 21 million doses of the vaccine to Australia and 36 million doses to the U.S., Perreault said. The U.S., which contracts with five companies, anticipates 45 million doses of its 195 million shots will be available for use by mid-October.

“We’ll certainly be able to meet all of the commitments that we’ve already made in the appropriate time frames, both to the U.S. and to the Australian governments,” Rachel David, a CSL spokeswoman, said on a conference call today.

CSL plans to donate the vaccine to developing nations in Asia and the South Pacific and is discussing a pilot program with the WHO to start by providing as many as 100,000 doses, David said.

The vaccines in both studies didn’t use ingredients called adjuvants included by some countries in formulations to boost effectiveness. No serious side effects were reported, though the trials are too small to detect rare conditions. The shots are being studied further and will be closely monitored once vaccination campaigns begin, according to U.S. officials.

‘Great News’

“This is great news,” Malik Peiris, professor of microbiology at Hong Kong University, said in an e-mail. “It remains to be investigated whether even lower doses can be used with reasonable levels of immunity, and if so, it means the available vaccine stock will stretch even further.”

Novartis reported Sept. 3 that a single dose of its vaccine, which included an adjuvant, safely provoked a strong immune response in a trial of 100 healthy volunteers.

Sinovac Biotech Ltd., the first company to win Chinese government approval for a swine flu shot, said Aug. 18 its vaccine was safe and effective after a single shot.

The U.S. study and the analysis conducted by CSL focused on adults, and more tests will be needed to determine whether one shot will be sufficient in children, who have less natural immunity developed from previous exposures to seasonal flu, Fauci said.

Two Shots

Children usually need two doses of seasonal flu vaccine, CSL’s David said. The company expects results from studies in children in Australia and the U.S. in October, she said.

The U.S. anticipates preliminary data in about two weeks from those trials in children, and from studies on pregnant women in mid- to late-October, Fauci said today in the briefing.

Immune responses to the vaccine in adults ages 65 and older were “slightly less robust” than in younger adults, Fauci said.

“This is not unexpected as this is the case with seasonal vaccines as well,” he said. The U.S. has no plans to change its treatment for elderly people, he said.

A separate shot will still be needed for protection against seasonal flu.

To contact the reporter on this story: Tom Randall in New York at trandall6@bloomberg.net.

Last Updated: September 11, 2009 14:53 EDT