Not enough proof that flu shots work, researcher warns

There isn't enough evidence that the flu vaccine is effective to support public programs advocating widespread use of flu shots, a controversial vaccine epidemiologist suggests.

There isn't enough evidence that the flu vaccine is effective to support public programs advocating widespread use of flu shots, a controversial vaccine epidemiologist suggests.

In a commentary inFriday's British Medical Journal, Dr. Tom Jefferson argues that large-scale, long-term randomized controlled trials— the gold standard for generating scientific evidence— should be "urgently" undertaken todetermine ifflu shot programs are achieving their goals of lowering rates of cases and deaths.

"There's a huge gap between policy and evidence," Jefferson, co-ordinator of the Cochrane Vaccines Field in Rome, said in an interview Thursday.

"I think the whole thing should be looked at again. That's what I recommend."

The Cochrane Vaccines Field is a division of the Cochrane Collaboration, an international non-profit network aimed at promoting evidence-based health care.

The collaboration funds and publishes Cochrane reviews, a highly specialized form of scientific analysis that amalgamates the findings of high-quality studies on a topic.

Jefferson didn't seem to feel funding agencies might balk at the notion of spending millions of dollars to go back to Square 1 to research the efficacy and safety of a public health intervention that has been in use for decades.

"I would have thought they [the trials] would be a lot cheaper than continuing with a program that may not work."

He also suggested there may be compelling ethical arguments in favour of doing this work, noting it could be unethical to give flu shots to people if it isn't clear they work.

Vaccine still worth it: Canadian expert

But Dr. Theresa Tam of the Public Health Agency of Canada took the flip side of the same argument, saying that from an ethics point of view, it might be impossible to enrol seniors in a study in whichsome 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 has 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, who directsthe 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 clinics throughout the Northern Hemisphere are just starting their annual vaccination efforts.

Strong safety record: Toronto specialist

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

Effectiveness of vaccine varies

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."