Introduction: Influenza disease is one of the major health concerns in pediatrics. One of the most recently suggested effects of vitamin D is preventing infectious diseases. The aim of our study was to compare flu vaccine effect to flu vaccine associated to vitamin D (100,000 UI per OS) in reducing respiratory tract infections in children. Patients and Methods: 347 healthy children aged 2 to 5 years randomly selected during fall 2012 and the following season fall 2013 were included;upper and lower respiratory tract infections following vaccination were noted. Our results were analyzed using SPSS program (Chi-square and T-test). Results: Out of a total of 347 children included, 150 received flu vaccine and 197 received flu vaccine plus vitamin D. 88 children from both groups manifested upper respiratory tract infections and 64 had lower respiratory tract infections. The statistical analysis revealed no significant difference between the two groups concerning the upper respiratory tract infection (p = 0.207) and a significant difference between groups for the lower respiratory tract infection (p = 0.001). Conclusion: Coupling vitamin D to flu vaccine provides no protection against upper respiratory infections but provides an effective strategy to decrease the rate of lower respiratory infections in children 2 - 5 years of age.