The authors examined more than 12,000 articles, studies and transcripts dating back to 1936 and interviewed 88 experts on the influenza vaccine.

What they found was that there were some seasons in which the vaccination offers more protection than others, but ultimately, even in good years, the flu shot only offers moderate protection -- a "pooled estimate of 59% for healthy adults 18 to 64 years of age, inconsistent evidence of protection in children age 2 to 17 years, and a paucity of evidence for protection in adults 65 years of age and older."

For the nasal spray form of the vaccine, there is evidence of high protection for children aged 6 months to 7 years, inconsistent evidence of protection in adults 60 years of age and older, and a lack of evidence of protection in individuals between 8 and 59 years of age, the study says.

That analysis shows significantly less effectiveness than what has been the conventional wisdom within the scientific community, Osterholm said.

"In promoting vaccination, it became a mantra that it was 70 to 90% effective across all ages completely, and that wasn't true," Osterholm said. Historically, this expansion in policy over who should get vaccinated was based on "professional judgment and not on scientifically sound data," he said.

Osterholm's study suggests this has been a general pattern in American public health history with relation to the flu vaccine.

"There is a real downside to the promotion (of the current flu vaccine), as it dampens serious investment and shuts down any real interest in start-ups to create a more effective vaccine," Osterholm said. "There is a sense that a 59% match is better than zero, but we wouldn't accept this with a disease like measles, which we seem to take more seriously."

The vaccine, however, is improving, according to Schaffner.

"Researchers are trying to make a genuinely better vaccine, including a universal vaccine that could combat all the different strains of flu that we could get every 10 years, as opposed to needing one annually," Schaffner said.

"So cross your fingers. All of us wish we had a better vaccine. We know what we have is good, but not perfect. Until we have one, we have to do as much good as possible by vaccinating as many people as possible -- and in the meantime I'll be watching the universal vaccine trials very carefully."