Recent studies bolster earlier evidence: Flu shots not beneficial

The Cochrane Collaboration describes itself as an international, non-profit, independent organization whose mission is to ensure the availability of up-to-date and accurate information about the effects of health-care interventions. It produces systematic reviews of such interventions and compiles scientific evidence, such as clinical trials and other studies, about their effects.

In an ongoing study published in 2009 and updated this year, entitled “Vaccines for preventing influenza in healthy adults,” scientists said they found no plausible substantiation that the flu vaccine prevented death or hospitalization from flu-related complications and only marginally reduced the number of days of lost work attributed to the illness.

The study’s goal, the researchers stated, was to “identify, retrieve and assess all studies evaluating the effects of vaccines against influenza in healthy adults.”

The researchers, led by Dr. Tom Jefferson, a British epidemiologist and chief of the Vaccine Field Group at Cochrane, reviewed studies conducted between Jan. 1, 1966, and June 2010. The authors included 50 reports, of which 40 were clinical trials involving more than 70,000 people.

What they found was shocking. When the vaccination matched the viral strains actually circulating that season, with a high circulation – an uncommon occurrence – 4 percent of unvaccinated people developed symptoms compared with 1 percent of vaccinated people. In the more common years where vaccines did not match the circulating strain, two percent of unvaccinated people got the flu compared with 1 percent of those vaccinated.

In testimony earlier this year before the Parliamentary Assembly of the Council of Europe, Jefferson put those numbers in perspective.

“After reviewing more than 40 clinical trials, it is clear that the performance of the vaccines in healthy adults is nothing to get excited about,” Jefferson said. “On average, perhaps one adult out of a 100 vaccinated will get influenza symptoms compared to two out of 100 in the unvaccinated group. To put it another way, we need to vaccinate 100 healthy adults to prevent one set of symptoms.”

What’s more, the study found no credible evidence the vaccines afforded any protection against complications such as pneumonia or death but did increase the potential side effects.

“Vaccination had a modest effect on time off work and had no effect on hospital admissions or complication rates,” the researchers stated in the study. “Inactivated vaccines caused local harms and an estimated 1.6 additional cases of Guillain-Barré Syndrome per million vaccinations.”

Those results, as bad as they were, might actually overstate the case for vaccine effectiveness, the researchers cautioned, because many of the studies – 15 of 36 trials with funding declarations – were industry initiatives.

Jefferson and his colleagues said they found a systematic tendency for prestigious medical journals to publish and cite industry-funded studies, while less publicized studies funded from public sources were significantly less likely to report conclusions favorable to the vaccines.

“Our results may be an optimistic estimate because company-sponsored influenza vaccine trials tend to produce results favorable to their products and some of the evidence comes from trials carried out in ideal viral circulation and matching conditions and because the harms evidence base is limited,” the study stated.