EFFECTS OF VITAMIN D STATUS ON PNEUMOCOCCAL VACCINE RESPONSES IN CHILDREN BELOW FIVE YEARS WITHIN KILIFI COUNTY, KENYA

Abstract

Background: Pneumonia is a major public health problem and a leading cause of death in children under 5 years in low and middle-income countries (LMICS). Despite vaccination, pneumonia remains a leading cause of high morbidity and mortality. The vaccines are particularly less efficacious in children living in developing countries. To improve vaccine effectiveness, identifying modifiable factors such as poor nutritional status is necessary. Vitamin D is an essential micronutrient for the body that is also important in maintaining a healthy immune system. Vitamin D plays a critical role in the immunomodulation of immune responses by dampening and regulating immunity. Low vitamin D levels are associated with deleterious effects on immunological functions thereby predisposing children to infectious diseases. The main aim of the study was to determine the association between vitamin D status and antibody responses to pneumococcal vaccine in Kenyan children below 5 years. Methods: A systematic review was conducted to determine the impact of vitamin D status on vaccination by searching PubMed and Web of Science databases for prior studies. The search key terms included vitamin D and vaccine. Serum 25-hydroxyvitamin D (25OHD) concentrations (vitamin D biomarker) were measured on plasma samples of children aged 12-59 months from a randomized controlled trial of 10-valent pneumococcal conjugate vaccine (PCV10). The 25OHD levels were quantified using VIDAS, an immunoanalyzer based on the enzyme-linked fluorescence assay (ELFA) technology. The association between vitamin D status and antibody responses to PCV10 vaccine was evaluated. Univariable and multivariable regression analyses were conducted to evaluate the impact of vitamin D status on antibody levels while adjusting for age, sex, and height for age Z scores. Results: The systematic review demonstrated conflicting findings on the association between vitamin D status and vaccine responses. Most of the studies obtained (n=13) reported a lack of association between vitamin D status and vaccination, 4 studies showed a negative association while the rest described an increase in 25OHD levels associated with an increase in vaccine-induced antibody responses. Based on the current cross-sectional study, a total of 357 children vi were included in the statistical analysis. The majority of the children (69.5%) were vitamin D replete, 28.9% were vitamin D insufficient and the remaining children (1.7%) had deficient levels of 25OHD. There was no evidence of an association between serum vitamin D status and antibody responses at baseline and after both first and second vaccine doses in Kenyan children. Conclusion: Vitamin D insufficiency was common among the study population rather than vitamin D deficiency. Vitamin D status whether at higher levels or suboptimal levels did not predict antibody responses to PCV10. The current research shows that vitamin D status may not be associated with the antibody responses of children after vaccination with the pneumococcal vaccine, suggesting that 25OHD levels in this setting are not immunosuppressive.