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Only One Shot Required! One Vaccine Shot Protective for Pandemic H1N1 Virus

September 11, 2009

Good news to report on the H1N1 vaccine front from Down Under! Defying the expectations of flu experts, clinical trials are showing that the new H1N1 flu vaccine protects with only one dose instead of two, so the vaccine supplies now being made will go twice as far as had been predicted.

  The robust immune response to the H1N1 vaccine after a single dose was unanticipated

The robust immune response to the H1N1 vaccine after a single dose was unanticipated

Much of the current global pandemic planning is predicated on previous experience that two doses of vaccine are required to elicit a protective immune response in populations that are immunologically naive to a new influenza strain.  That means it should be possible to vaccinate — well before the flu’s expected midwinter peak — all the 159 million people that the CDC estimate are in the high-risk groups: pregnant women, people under 24 years old or caring for infants, people with high-risk medical conditions and health-care workers. Barring any production delays, the government hopes to have in hand 195 million doses by year’s end.

The vaccine trial using a single 15-microgram dose in adults, was conducted in Australia, and published online by The New England Journal of Medicine. The vaccine maker, CSL Limited, is under contract to supply millions of doses to the United States government, and the president of the company’s American subsidiary said he expected its trials here to have similar results.

Cases are now surging again, especially in the Southeast where many schools and universities reopen earlier than in the rest of the country

Cases are now surging again, especially in the Southeast where many schools and universities reopen earlier than in the rest of the country

Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said trials now under way under the sponsorship of the National Institutes of Health were showing that adults who got only a single dose were protected within 8 to 10 days, which he said “corroborates and confirms the exciting data,” reported in the Australian study.

Robust protection produced so quickly in high-risk groups means lives will presumably be saved, Dr. Fauci said. Costs will also be lowered by having a more efficient vaccine, he said, “but I can’t give you a dollar figure.”

Also, more vaccine could be available to poor countries that were largely left out of last spring’s global scramble to sign vaccine makers to contracts. Experts have worried that rich countries would be protected this winter while poor ones — where people are more likely to die because of drug shortages and substandard hospital care — would bear the brunt of the pandemic.

The results released Thursday were based on the first three weeks of a clinical trial. Healthy adults got one 15-microgram shot, and their blood was tested 21 days later. By that time, 97 percent of the 120 adults had enough antibodies to be considered protected. Another group that got 30-microgram doses had no greater protection.

Another piece of good news! There were no deaths or dangerous side-effects in the trial. Almost half of the participants reported sore arms or headaches, but that is normal with flu shots. The American trials began about two weeks later, said Paul R. Perreault, president of CSL Biotherapies, the company’s American subsidiary. “My experience with this tells me they shouldn’t be any different,” Mr. Perreault said.

Seasonal flu shots are available now, and Federal officials are urging Americans to get one. Little or no swine flu vaccine will be available before late October. There have been no clinical trials of giving both shots at the same time, and Federal health officials have issued no recommendations on that.

Experts had predicted for months that, because the H1N1 swine flu has never been seen before by human immune systems, it would take two doses, administered weeks apart, to get a “take” — antibody levels as high as those produced by regular flu shots.

The authors of the Australian study said the robust response implied that there was some previously unsuspected crossover protection from having had previous strains of H1N1 seasonal flu’s or from the H1N1 components of seasonal flu shots.

Although the Australian trial was in healthy adults only, Dr. Treanor said he believed one dose of the new vaccine would prove effective in everyone from age 9 and up.

Children ages 6 months to 9 years who have never had a flu shot usually get two shots

Children ages 6 months to 9 years who have never had a flu shot usually get two shots

Pediatricians usually give two shots to children ages 6 months to 9 years who have never had a flu shot, the first primes the immune system and subsequent shots act as boosters that create new surges of antibodies, though slightly varied each year as strains mutate. Infants under 6 months old are not normally given flu shots. Pregnant women are, and babies can inherit some temporary immunity from their mothers.

http://content.nejm.org/cgi/content/full/NEJMoa0907413

http://www.nytimes.com/2009/09/11/health/11vaccine.html?_r=1&th&emc=th

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