Coming at the end of the largest flu-vaccination campaign in Canadian history, the review of previous studies calls for stepped-up research into alternative, lower-tech ways to combat the virus, such as improved hand washing.
"What troubled us is that [shots] had no effect on laboratory-confirmed influenza," said Dr. Roger Thomas of the University of Calgary, lead author of the paper published by the respected Cochrane Library.
"What we were looking for is proof that influenza ... is decreased. Didn't find it. We looked for proof that pneumonia is reduced. Didn't find it. We looked for proof deaths from pneumonia are reduced. Didn't find it."
A prominent flu expert, however, calls the authors' conclusions misleading, noting that vaccinating workers does, in fact, lessen the amount of influenza-like sickness and the number of deaths from all causes among those nursing-home denizens. That is all that really matters, said Dr. Allison McGeer, infectious disease specialist at Toronto's Mount Sinai Hospital.
"There is [very little] that you or I can do that is more effective at preventing deaths than vaccinating health-care workers in long-term care facilities," she said. "That's the bottom line .... There is no question."
The studies could not accurately gauge the effect of vaccination on actual laboratory-confirmed flu cases in nursing homes, because so few residents are tested, added Dr. McGeer. If labs had examined specimens from everyone in the studies, the results would likely have shown a reduction in confirmed flu cases, too, she said.
The new paper's co-author is Dr. Tom Jefferson, a British epidemiologist who heads vaccine research for the respected Cochrane Collaboration -- and who has earned a reputation as a scientific dissident for his outspoken criticism of flu vaccination.
In media interviews last year, Dr. Jefferson was quoted as saying he "can't see any reason" for vaccinating anyone against flu -- arguing the shots did nothing to save lives -- and that most influenza-vaccine studies are "rubbish."
Dr. McGeer said she finds it "mind boggling" that medical journals that publish Dr. Jefferson's work do not question his provocative analyses.
"Scientists are passionate about what they do. All of us have belief systems and sometimes, as with any human endeavour, your belief system overwhelms the scientific evidence," she said. "The purpose of scientific method, the purpose of publication is to get back the objectivity ... And we are not doing that effectively with Dr. Jefferson."
The stakes in the debate are high. Governments spent more than $400-million on acquiring H1N1 pandemic vaccine for Canadians. The Ontario government alone spends about $23-million annually in providing seasonal-flu shots free to anyone who wants them.
The Public Health Agency of Canada, which oversaw the pandemic flu battle, will study the Cochrane review's findings carefully, said Nadia Mostafa, an agency spokeswoman. The agency recognizes that "it is not effective to only immunize and not take any other infection-prevention measures," she noted.
The review by Dr. Thomas and Dr. Jefferson analyzed five studies on the issue conducted between 1997 and 2009 -- four of them randomized, controlled trials -- using guidelines set out by Cochrane, which does systematic reviews of the effects of drugs and other health measures.
They concluded that vaccinating staff had no proven impact on the amount of laboratory-confirmed flu cases among elderly residents, the number of related pneumonia cases or pneumonia-linked deaths, which the authors said would be the most direct outcomes of flu-shot campaigns.
Dr. Thomas underlined his study's call for high-quality research into other anti-flu measures, such as enhanced use of hand washing, face masks, early detection of the virus with nose swabs and quarantining nursing-homes.
He said he aggressively encouraged such strategies during a previous role as director of long-term care homes in Ottawa, and the facilities' death rates were among the lowest in the city.