By Helen Branswell, Medical Reporter, The Canadian Press

TORONTO - It looks like American children will have to endure two shots or nasal squirts of H1N1 vaccine but the question of how many doses of vaccine Canadian kids will need remains to be answered, experts say.

The U.S. National Institutes of Allergy and Infectious Diseases (NIAID) released clinical trial data Monday showing that children under 10 didn't respond well enough to one dose of adjuvant-free H1N1 vaccine to consider them protected against the virus. Based on those data, the U.S. is sticking to its earlier recommendation that children under 10 get two doses of H1N1 vaccine, given at least 21 days apart.

But the World Health Organization is recommending countries focus efforts on giving as many kids as possible a single dose, given the current scarcity of supply. And Canada is holding out for more data.

The various positions may be a formula for confusion among parents. In anticipation that there are lots of questions, here are some answers:

Q: How many doses of vaccine will Canadian kids need?

A: That's not clear yet. Canadian kids (and adults) will have access to vaccine with an adjuvant, an additive that boosts the immune response induced by vaccine.

And a very small study by Canada's vaccine manufacturer, GlaxoSmithKline, suggests even kids as young as six months may be able to get away with a single dose of adjuvanted vaccine. A kid's dose is half an adult dose, with half the adjuvant an adult would receive.

Based on GSK's early data, Canadian officials say it's possible kids in Canada will only need one dose, but they want more information before making that decision.

But given that there must be a 21-day interval between the doses, there is still time to figure this out, experts say.

"For me, given the level of activity, the second wave activity already occurring, our goal should be ... get a first dose into kids. Then we can discuss the second dose," said Dr. Danuta Skowronski, a flu expert with the British Columbia Centre for Disease Control.

"We still have time to work out whether that second dose will be necessary."

Q: Why are U.S. officials saying kids under 10 need two doses?

A: U.S. pandemic planners decided against using adjuvant in their vaccine. And vaccine without adjuvant doesn't induce a terrific immune response in little kids, whose immune systems are still developing and who haven't had as much exposure to flu viruses as older children and adults.

The study results released Monday were based on a trial in 583 children aged six months to nine years of age who were given two doses of H1N1 vaccine without adjuvant at a 21-day interval.

The response to one dose was poor in children six months to 35 months - only 25 per cent reached the protective mark. In children three to nine years, the rate was 55 per cent, still too low by regulatory standards.

But Dr. Anthony Fauci, head of the NIAID, said after the second dose 100 per cent of the younger children and 94 per cent of the older children had antibody levels that suggest they are protected against the virus.

Q: Do those findings have any bearing in Canada?

A: Only if parents are planning to hold out for adjuvant-free vaccine for their kids.

A spokesperson for the Public Health Agency of Canada noted that parents who want to go that route need to realize kids will need two adult-sized shots of vaccine, given 21 days apart. And the full protection of those shots will only really be in effect two or three weeks after the second shot is give.

Q: But if I still want adjuvant-free vaccine for my child, will it be available?

A: Technically yes. But getting it may be a challenge.

Under pressure from some pediatricians and parents, Canada bought 600,000 doses of unadjuvanted vaccine for kids under three years old. Those doses are still in the production pipeline.

After the GSK trial results came out showing one half-dose of adjuvanted vaccine induced a protective immune response in 100 per cent of kids six to 36 months old in the study, federal officials stopped talking about unadjuvanted vaccine for toddlers.

The official recommendation for that age group is adjuvanted vaccine. And while federal authorities will say, if pressed, that unadjuvanted vaccine is still an option for little kids, they don't volunteer the information easily.

And it is conceivable that local clinics will interpret the recommendation as an edict, not advice.

"My understanding is the only time there's an option is in pregnancy," said Dr. Joanne Langley, who is chair of the National Advisory Committee on Immunization - someone you'd think would know if there was still a plan to offer unadjuvanted vaccine to kids under three.

"I haven't seen it on any provincial guidance about what they're doing for their vaccine programs, that they would offer unadjuvanted."

Q: Is the adjuvanted vaccine safe for small children?

A: The public health agency thinks so. So does the World Health Organization. So do a number of influenza and vaccine experts.

"My concern is we are having intense second wave activity now. So for parents to be holding out for an unadjuvanted when we're facing intense activity now, they'll miss the boat in terms of protecting their kids," said Dr. Danuta Skowronski, a flu expert with the British Columbia Centre for Disease Control.

"Better the bird in the hand than two in the bush."

Langley, a pediatrician who specializes in infectious diseases, agrees.

"I think as a pediatrician, knowing these children are vulnerable, knowing that the likelihood of them having a strong and quick immune response ... is so much lower with an unadjuvanted preparation . . . I think the best choice in that circumstance is to go with an adjuvanted preparation."

Q: If the U.S. says two doses and Canada says it needs more evidence before deciding, why is the WHO recommending one dose for children under age 10?

A: The WHO's position mixes evidence with pragmatism. Many countries are using adjuvanted vaccine for children, and the evidence currently points to one dose being sufficient.

But the organization also knows there's no where near enough H1N1 vaccine in the world, and they think it makes more sense to offer as many kids as possible one shot rather than worrying about giving kids two.

Fauci, the head of the NIAID, said the WHO is basing its recommendation on a strategy for maximizing available vaccine, while the U.S. is basing its on scientific evidence.

"We would like to get children as fully protected as we possibly can. Obviously the optimal thing is to get the children who are within the group that requires two doses to get all of them two doses in time."

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