Science on flu shot effectiveness doesn't support flu shot policies: researcher

But Dr. Theresa Tam of the Public Health Agency of Canada took the flip side of the same argument, saying from an ethics point of view it might be impossible to enrol seniors in a study where some get a placebo instead of a shot.

In the world of clinical trials it is unethical - and not permissible - to withhold a drug, vaccine or other treatment if it's been proven to be effective either in treating or preventing a condition.

"We certainly believe, looking at all of the evidence, that for the elderly - who are at high risk - even if the vaccine effectiveness is lower (than in healthy adults), it's still worth it, said Tam, director of the agency's immunization and respiratory infections division.

In the journal, Jefferson argued too few good quality trials have been conducted to be certain flu shots are worth the time, effort and cost of flu vaccine programs.

His argument is bound to stir up ire in the community of scientists and public health authorities who deal with influenza, particularly now as flu clinics throughout the Northern Hemisphere are just starting their annual vaccination efforts.

"That the BMJ would consider publishing an editorial from somebody saying that we should be thinking about not vaccinating at-risk people for influenza is a really bad thing," said Dr. Allison McGeer, an infectious diseases specialist at Toronto's Mount Sinai Hospital.

Jefferson and colleagues at the vaccines field have in the past couple of years published Cochrane reviews challenging the efficacy of flu vaccine in children and in the elderly. The mere mention of his work provokes heated reactions in some influenza circles.

That may be in part because the Cochrane approach places limited value on data not generated through randomized controlled trials. While other scientists acknowledge those studies are best, they note it isn't always possible to conduct them, and that an accumulation of other forms of evidence can make a persuasive case as well.

McGeer pointed to a complaint in Jefferson's commentary about the lack of good, comparative data on the safety of flu shots.

"How can you say that we don't have a safety record when we give 20 million vaccinations a year?" she asked with exasperation in her voice.

Flu shot advocates do admit the vaccine isn't as effective as they would like.

Efficacy varies from year to year, depending on how well matched the strains in the shot are to those circulating and causing disease. And the amount of protection depends on age - the shots provoke a better immune response in healthy adults than they do among the elderly, whose immune systems are on the wane.

"Even a vaccine that is not as effective as we would like could still have a substantial benefit," said Tam, who noted that as far as the agency is concerned, there is enough evidence to conclude vaccinating people against the flu lowers the annual toll of the disease.

Conducting the types of trials Jefferson advocates wouldn't be easy, given that the amount of flu activity varies from year to year, the vaccine isn't always a perfect match for circulating strains and different ages respond differently to the shots.

Tam said that while the public health agency continues to conduct studies on the efficacy of flu vaccine, the type of abrupt re-examination of policy Jefferson is advising isn't in the cards here.

"We certainly think that very large scale, multi-year randomized controlled trials . . . is just not that feasible for most public-health programs."

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