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The H1N1 flu virus is circulating through schools, offices and homes across Canada, but for some, the word “adjuvant” stirs more concern than the prospect of contracting the novel influenza virus.

Adjuvants, immune-boosting substances that help vaccines work, have been the subject of significant debate, controversy and confusion since the federal government announced they would be added to the Canadian vaccine. For many parents, the debate has taken on unique resonance as they hear confusing messages from public-health officials and conspiratorial websites about the safety record of the immune-boosting agents.

It has led some to question whether children – those under age 3, in particular – should wait until unadjuvanted vaccines are made available, or forgo vaccination altogether.

The confusion prompted the Canadian Paediatric Society to issue new information for physicians on the safety of the H1N1 vaccines and adjuvants, scheduled to be released on its website yesterday. “I know of no credible evidence to suggest it poses any risk to the children,” said Robert Bortolussi, a pediatric infectious disease specialist at the IWK Health Centre in Halifax and chair of the CPS's committee on infectious disease and immunization. “Even on a theoretical basis, it's hard to imagine it would.”

Dr. Bortolussi added small studies have shown adjuvants are safe in babies.

The adjuvant being added to Arepanrix, the H1N1 vaccine approved in Canada, is called AS03. It's a natural combination of several substances, including vitamin E and squalene derived from shark liver. Although this particular adjuvant hasn't been used in a Canadian influenza vaccine before, it has been tested on about 45,000 individuals using a vaccine designed to fight the H5N1 avian influenza. Adjuvants have also been widely used in Europe, and have been included in some other Canadian vaccines.

The adjuvant boosts the body's immune response because it allows the antigen, the active ingredient in vaccines, to remain at the injection site longer and attract a large amount of immune cells to help the body develop antibodies to the virus, said Dr. Bortolussi. That also means less antigen is required in adjuvanted vaccines, allowing drug companies to produce more vaccine quickly.

The vast majority of H1N1 vaccines distributed in Canada will contain adjuvants, but the government has purchased a small supply of unadjuvanted vaccine to be used by some pregnant women and children under three, if parents choose.

There is no data that has looked at the safety of adjuvants in pregnant women and limited data on children under 3. But Canadian health experts have agreed the risk of adjuvanted vaccine appears small, so are recommending that women over 20 weeks gestation receive it if an unadjuvanted vaccine isn't available. Public-health experts also agree that adjuvanted vaccine is safe for use in children as young as six months, and say adjuvanted vaccine is best for that age group because it produces the best immune response. The H1N1 vaccine is not recommended for babies under six months.

Although parents can choose to give their children unadjuvanted vaccine, Canada's chief public health officer David Butler-Jones told The Canadian Press that he “wouldn't wait” until it became available to give it to his grandchildren.