Vitamin D and influenza vaccination

Keywords: :

• acute otitis media
• influenza
• influenza vaccine
• vitamin D
• vitamin D supplementation

Our study confirms that even in industrialized countries most of the younger children have low serum levels of vitamin D (VD) at the beginning of the winter season, and because the advantages of influenza vaccination in pediatric age are well demonstrated, both VD supplementation and influenza vaccine should be recommended.

We thank you for the kind letter regarding our paper on vitamin D (VD) impact on immunogenicity of trivalent inactivated influenza vaccine (TIV) in previously unvaccinated children.¹ However, we do not agree with the consideration that the uselessness of VD administration in unprimed children was expected. Several reasons lead to this conclusion. First of all, the fact is that in the literature, data on this topic are few and conflicting. As reported in the introduction of our paper, together with the negative results you cited, there are those published by Chadha, et al. who demonstrated that a replete VD status is associated with a more frequent response to TIV in prostate cancer patients.² Moreover, previous studies enrolled only adults and the different characteristics of children's immune system could have conditioned a different antibody production. Finally, we enrolled otherwise healthy subjects and administered VD day by day for 4 mo after vaccination, whereas in previous studies in two cases immunocompromised patients were included^2,3 and in the third study the active form of VD was given in a single dose at the moment of vaccine injection.⁴

We think that to definitively establish the real role of VD in conditioning influenza vaccine response in children further studies with different schemes of administration and dosages are needed. However, because this study confirms that even in industrialized countries most of the younger children have low serum levels of VD at the beginning of the winter season, and because the advantages of influenza vaccination in pediatric age are well demonstrated,⁵ we completely agree with you about your final consideration. Both VD supplementation and influenza vaccine should be recommended.