Effect of Zinc Supplementation on Response to Oral Polio Vaccine in Infants in Pakistan

Pakistan is one of the 4 developing countries where cases of poliomyelitis are still being identified. Despite the incessant efforts by WHO and UNICEF, this disease is far from control. There is a need to develop new and innovative strategies to contain the disease and eradicate it from the countries where new cases continue to be identified. Zinc is an essential component of scores of enzymes in the human body. Recent reports have indicated that this trace element along with other micronutrients enhances the protective functions of immune cells. Moreover, zinc deficiency leads to dysregulation of balanced host responses to infection resulting into decreased antibody production and suppressed immunity. Zinc is also an essential cofactor for thymulin which is known to modulate cytokine release and induce immune cell proliferation. Zinc deficiency is also found to impair an individual's epithelial barrier function, which may further depress the vaccine entry into the mucosal cells. Role of zinc in the prevention of diarrheal diseases and other infections in children is well documented. However, there are very few reports about its contribution to enhanced immunity by supporting body's natural defense system. Zinc insufficiency is widespread in socioeconomically deprived children in South Asia and the recent most national nutrition survey (2003) . Moreover, diarrhea is also very common in infants in Pakistan. Such diarrheal episodes can limit entry of attenuated polio virus into the mucosal cells, thereby, leading to inadequate immune response. Association between recent diarrheal history and increased vaccine failure in infants has been shown in a study from Brazil. The recent Lancet Nutrition series has also recommended regular zinc supplementation to address child undernutrition and stunting and underscored the need to treat diarrheal episodes with zinc to expedite recovery. Other recent studies of zinc supplementation in low birth weight infants in South Asia ha