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One Dose of Swine Flu Vaccine Offers Protection: Studies

Findings could expand vaccine supply and speed immunity, experts say

THURSDAY, Sept. 10 (HealthDay News) -- Preliminary tests of an H1N1 swine flu vaccine conducted in Australia and Britain show that a single dose creates enough antibodies to protect against the virus within about 10 days.

That's a potentially significant development, because it was thought that two shots would be needed to provide full immunity to the virus. A one-dose protocol would greatly expand the supply of vaccine and hasten individual immunity.

The H1N1 swine flu has already started to spread this fall in the United States and is infecting as many people now as would be expected in the peak of the flu season, according to the federal Centers for Disease Control and Prevention.

"A single vaccination at standard dose produced a strong immune response in more than 96 percent of adults studied," said the lead researcher of one of the two studies, Dr. Michael Greenberg, director of Clinical Development of Vaccines at CSL Behring, Ltd. in Victoria, Australia.

CSL is setting aside 36 million doses of its vaccine for distribution in the United States, Bloomberg News reported.

Most of the H1N1 pandemic planning in the world has assumed that two doses would be needed, Greenberg pointed out.

"At least in adults, this doesn't appear to be the case. This has important implications for public health policy as it would increase the number of people who could be vaccinated and also improve logistics by not having to bring most people back for a second shot, " he said.

For the trial, Greenberg and colleagues tested the vaccine in 240 people both under and over 50 years of age. These people were given two different doses of the vaccine and their antibody response was measured after 21 days.

The researchers found that a single dose of vaccine was enough to produce a sufficient number of antibodies to protect people from the H1N1 flu.

About 45 percent of recipients did experience side effects but these were typically mild and consisted of some soreness or redness at the injection site and/or a headache, the researchers reported.

For the second trial, British researchers led by Dr. Iain Stephenson of the Leicester Royal Infirmary tested the vaccine on 175 adults 18 to 50 years of age. Patients were randomly assigned to various two-dose regimens of the vaccine.

Those researchers also found that even a single dose of the vaccine was sufficient to protect adults from the H1N1 flu within the first two weeks after inoculation.

Both reports were published Sept. 10 in the online edition of the New England Journal of Medicine.

U.S. data to be released Friday will confirm those one-dose findings, and show that protection starts rapidly after vaccination, Dr. Anthony Fauci of the National Institutes of Health told the Associated Press.

"This is quite good news," Fauci said.

Dr. Marc Siegel, associate professor of medicine at New York University Langone Medical Center in New York City, said, "It looks like a single dose works -- wow."

"This is great news," Siegel said. "It looked like it was going to take two shots. But I am still expecting two shots [will be needed] in kids, because they don't have the immune basis," he noted.

In the United States, results from the first vaccine trials are expected later this month, and assuming the vaccine is safe and effective, it should begin to be available by mid-October, according to the Centers for Disease Control and Prevention.

In a third report in the same journal issue, researchers at the CDC found that this year's "regular" seasonal flu vaccine does not offer any protection against the H1N1 swine flu, regardless of the age of the patient. However, they did find that while people age 30 years or younger had little if any natural protection against the H1N1 flu, some older adults had preexisting antibodies to the H1N1 flu, probably picked up during H1N1 outbreaks in their youth.

The inability of the seasonal shot to protect against H1N1 swine flu is further evidence that to protect themselves from both flus, Americans will have to have both shots -- the seasonal flu shot, which is available now, and an H1N1 shot when that vaccine becomes available.

The CDC expects about 116 million doses of seasonal flu vaccine will be available this year. Usually about 100 million Americans get vaccinated, although most people should.

According to the CDC, people who should get a seasonal flu shot include:

  • Adults 50 and older.
  • All children age 6 months to 18 years.
  • Pregnant women.
  • People with chronic health problems like asthma, heart disease or a weakened immune system.
  • Health care workers.
  • Caregivers of people at high-risk, including babies younger than 6 months of age.

Those first in line for swine flu shots should be:

  • Pregnant women.
  • Children and young people between 6 months through 24 years of age.
  • Health-care workers.
  • Younger and middle-aged adults with chronic health conditions or weakened immune systems.

More information

For more on H1N1 swine flu, visit

SOURCES: Michael Greenberg, M.D., M.P.H., director, Clinical Development of Vaccines, CSL Behring, Ltd., Victoria, Australia; Marc Siegel, M.D., associate professor, medicine, New York University Langone Medical Center, New York City; Sept. 10, 2009, New England Journal of Medicine, online

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