TORONTO - Mass vaccination programs against swine flu are going to be a lot easier to mount than first thought, experts said Thursday after the fast-tracked publication of studies showing one dose should be enough to protect most adults.
Two vaccine makers, CSL of Australia and Novartis Vaccines and Biologics of Cambridge, Ma., reported that a single dose of vaccine induced a protective response in a high proportion of adults tested.
CSL saw the robust response with one dose of 15 micrograms -- the amount per strain in a seasonal flu shot -- of plain vaccine. Novartis was testing half- and standard-sized doses of vaccine with a boosting additive known as an adjuvant.
The findings will be backed by results of trials in adults and seniors to be released Friday by the U.S. National Institutes of Health, said Dr. Anthony Fauci, director of the NIH's National Institute of Allergy and Infectious Diseases.
"The data from the NIH clinical trial on unadjuvanted H1N1 pandemic vaccine verifies and corroborates the exciting data that have come out on the unadjuvanted vaccine in the New England Journal of Medicine," Fauci said in an interview from Bethesda, Md.
Fauci noted the NIH research saw a similarly strong response within eight to 10 days of a single dose, which is very quick by vaccine terms. Studies have shown it can take four weeks or longer for a person to develop a strong response when vaccinated against a new pathogen.
The findings suggest the limited global supplies of pandemic vaccine can be stretched to cover double the number of people who could have been vaccinated if two doses were needed. And public health officials would heave sighs of relief at the prospect of not having to round up people to get two shots of pandemic flu vaccine and a shot of seasonal flu vaccine this fall.
"It's going to end up being a much simpler campaign," said Dr. John Treanor, an vaccine expert at the University of Rochester in northwestern New York state.
"This is all very, very promising," agreed Dr. David Butler-Jones, Canada's chief medical officer of health. He cautioned, though, that it remains to be seen if one shot will work for teens and children, seniors and people with compromised immune systems.
The Public Health Agency of Canada is buying vaccine with adjuvant from vaccine giant GlaxoSmithKline, which has yet to release findings of its clinical trials. A clinical trial that will be used to license the GSK vaccine made for Canada will begin next week, Butler-Jones said.
CSL reported that nearly 98 per cent of volunteers who got one shot of 15 micrograms of vaccine mounted an antibody response which should be protective. And Novartis said that 76 per cent and 92 per cent of volunteers crossed the protective threshold, depending on the test used to measure the response.
In both trials a fair proportion of recipients reported side-effects, but of the type seen with seasonal flu shots -- mainly discomfort at the site of the injection.
Treanor and Fauci said the results suggest people's immune systems respond to this vaccine the way they do to seasonal H1N1 flu vaccine.
Even though studies suggest most people under 60 don't generate antibodies to this new H1N1 virus, earlier exposures to H1N1 viruses or vaccines must have "primed" immune systems, they said. The single-dose response suggests the vaccine is working like a booster shot, reawakening the immune system to a threat similar to something it confronted in the past.
"This is an immunogenic vaccine that you're already primed to respond to and will, I'm sure, behave exactly the same way that any seasonal flu vaccine would behave in terms of its ability to induce antibody," Treanor said.
"If you jump on that wagon and say that `Well, this is going to be like any other H1 flu vaccine' your conclusion would be that probably kids over nine years of age or so, you're going to be able to vaccinate with a single dose. But you don't know that for sure."
Children under nine could be a different matter, because they've had so much less exposure to flu viruses and vaccines. Even with seasonal flu vaccine two doses are recommended for children younger than nine who've never been vaccinated before. That may be what's needed with this vaccine as well.
Fauci, a renown immunologist, said the strong adult response suggests there's something in the immune system that isn't being measured when laboratories look for antibodies to this new virus.
Despite the promising results, however, the fact remains that swine flu viruses have a big jump on swine flu vaccine availability in North America. Transmission never really died off in the summer and outbreaks are starting to take off again in places where schools and universities have been in session for several weeks.
"The problem is, the virus isn't co-operating," said Dr. Michael Osterholm, director of the Center for Infectious Diseases Research and Policy at the University of Minnesota.
"And given what we're seeing with transmission in North America, it's very likely that by the time the first drop of vaccine is in an arm, we could be on the downside of this wave."
