Not in babies: In a review of more than 51 studies involving more than 294,000 children it was found there was "no evidence that injecting children 6-24 months of age with a flu shot was any more effective than placebo. In children over 2 years, it was only effective 33 percent of the time in preventing the flu. Reference: "Vaccines for preventing influenza in healthy children." The Cochrane Database of Systematic Reviews. 2 (2008).

Not in children with asthma: In a study of 800 children with asthma, where one half were vaccinated and the other half did not receive the influenza vaccine, the two groups were compared with respect to clinic visits, emergency department (ED) visits, and hospitalizations for asthma. CONCLUSION: This study failed to provide evidence that the influenza vaccine prevents pediatric asthma exacerbations. Reference: Christly, C. et al. Arch Dis Child. 2004 Aug 89 (8):734-738

Not in children with asthma (2): "The inactivated flu vaccine, Flumist, does not prevent influenza-related hospitalizations in children, especially the ones with asthma...In fact, children who get the flu vaccine are more at risk for hospitalization than children who do not get the vaccine." Reference: The American Thoracic Society’s 105th International Conference, May 15-20, 2009, San Diego.

Not in adults: In a review of 48 reports including 66,000 adults, "Vaccination of healthy adults only reduced risk of influenza by 6 percent and reduced the number of missed work days by less than one day (0.16) days. It did not change the number of people needing to go to the hospital or take time off work." Reference: The Cochrane Database of Systematic Reviews. "Vaccines for preventing influenza in healthy adults" 1(2006)

Not in the Elderly: In a review of 64 studies in 98 flu seasons of the elderly living in nursing homes, flu shots were non-significant for preventing the flu. For elderly living in the community, vaccines were not (significantly) effective against influenza, ILI (influenza-like illnesses) or pneumonia. Reference: The Cochrane Database of Systematic Reviews. "Vaccines for preventing influenza in the elderly" 3(2006).