It is unnecessary to delay giving seasonal flu shots this year because of concerns they might raise the risk of catching swine flu, and provinces and territories should offer the shots as soon as possible, a new recommendation from a panel of Canadian vaccine experts said Sunday.
The National Advisory Committee on Immunization did not criticize the decision by most provinces and territories to put off delivering seasonal shots until the new year - a move based at least in part on unpublished Canadian studies that show a possible link.
But the committee, known as NACI, suggests even if the finding is real the risk of not vaccinating against seasonal flu is greater than the one identified by the studies.
And it is urging provinces and territories to move ahead with seasonal flu shots as soon as is feasible - even giving a thumbs up to the notion of delivering both at the same time, if that can still be arranged.
"We thought that overall, the benefit of getting seasonal flu vaccine was much more significant than this potential harm being seen in only the Canadian studies and it really being a small risk," said NACI chair Joanne Langley, a pediatric infectious diseases expert at the IWK Health Centre in Halifax.
At least two members of NACI are authors of the unpublished studies that prompted the abrupt change in influenza vaccination plans for this fall.
Dr. Langley wouldn't say how Danuta Skowronski of the B.C. Centre for Disease Control and Natasha Crowcroft of the Ontario Agency for Health Protection and Promotion voted - or whether they recused themselves from the vote. NACI does not hold its meetings in public and when decisions are not unanimous, it does not disclose a vote tally or how individual members voted.
The move by most provinces and territories to delay seasonal vaccine programs this year was based on a series of as-yet unpublished Canadian studies which found people who had received a flu shot last fall were between 1.5 and two times more likely to catch H1N1 this spring.
The link, if real, was to mild disease. There was no suggestion the people who had had seasonal flu shots were more likely to end up in hospital with or dying from H1N1 infection.
The possible association was first spotted by Dr. Skowronski, an influenza epidemiologist, in data from British Columbia. Subsequent work by colleagues in Quebec, Ontario and Manitoba corroborated her findings.
But data from the United States, Britain, Australia and Mexico do not show the link and in fact the Mexican study suggested people who had a seasonal shot were less likely to catch H1N1.
The Canadian work has not yet been published in a medical journal and whether it will be is not currently clear.
NACI met in early October, after all the provinces and territories had taken their decisions and perhaps too late to influence what will happen with seasonal flu shots this year.
Dr. Langley said they reviewed the Canadian studies, as well as data from the as-yet unpublished U.S. and British studies, and published papers from Mexico and Australia.
But the studies weren't the only elements that factored into NACI's decision.
"You have to look at that as one of the factors. It's not the only factor. And when you look at the big picture, the decision was it's more unsafe not to give [seasonal]vaccine at all than to give it," Dr. Langley said.