Vaccination of household chickens results in a shift in young children's diet and improves child growth in rural Kenya

Abstract

Childhood growth faltering remains unacceptably high in sub-Saharan Africa. Rural communities dependent on household food production with limited off-farm income or liquid assets to bridge seasonal food availability are especially vulnerable. A cross-sectional survey in Siaya County, Kenya identified 23.5 and 4.8% of children under 5 y of age as stunted and wasted, respectively, using height-for-age Z (HAZ) scores to detect stunting and weight-for-height Z (WHZ) scores for wasting. Although these households are classified as living in poverty or extreme poverty with very limited off-farm income, households commonly have on-farm resources that could be developed to improve nutrition. While 95% of these households have chickens and consumption of eggs was shown to increase childhood growth by an average of 5%, the average flock size is small and constrained by high mortality due to infectious disease. We hypothesized that interventions to relieve this constraint would translate into household decisions influencing the diets and growth of children. Here, we show that vaccination of chickens against Newcastle disease has a causal impact on children’s consumption of animal source foods rich in protein and micronutrients relative to a high-carbohydrate, grain-based diet. Children in treatment households (chicken vaccination) showed overall increases in scores for both HAZ and WHZ relative to control households, benefiting both girls and boys. The findings demonstrate the impact of directing interventions at common on-farm assets managed by women in rural communities and support programs to enhance productivity at the household level.

Keywords: animal source foods; child growth; household decisions; nutrition.

Fig. 1.

Consort diagram of study participation. Of the 667 households assessed for eligibility, 31 were excluded as not meeting the criteria of having a child <3 y of age and keeping chickens, and 55 declined participation. Households were then randomly allocated by computer to either the treatment arm of the study (vaccination of chickens against NDV plus parasite control) or the control arm (parasite control only). Households not present at baseline or that declined at baseline were excluded from the study, resulting in 254 treatment households and 283 control households entering the study. Households that did not participate in any subsequent quarters after three contact attempts were excluded from analysis, resulting in 222 treatment households with 348 children and 249 control households with 373 children for analysis. All households received the intervention (NDV vaccination and parasite control or parasite control alone) every quarter. Households that were assessed for child diet and growth on all quarterly visits and on multiple but not all quarterly visits were retained in the study (SI Appendix, Fig. S1, Supplementary Text S1, and Table S1). The procedures used to detect and control for any bias in intermittent participation are detailed in Materials and Methods and in SI Appendix, Supplementary Text S1 and Tables S2 and S3.

Fig. 2.

Transition from breastfeeding to solid foods by child age. The total number of solid food servings increases through about age 1.5 y (18 mo) and then, remains relatively constant with slight decline, while the fraction of children being breastfed declines to zero.

Fig. 3.

Overall effect of being in a treatment group household on child growth relative to the control group. The histograms represent the distributions of HAZ and WHZ scores for control group age over 18 mo of age for those who have been in the trial at least 15 mo. Thick solid black vertical lines are control group means, and the dashed black lines are one SD from the distribution mean (SDs are 1.22 for HAZ and 0.922 for WHZ). The red lines represent the mean Z score plus the total effect of treatment (direct plus indirect effects; 0.209 for HAZ and 0.098 for WHZ). The lightly shaded maroon areas are 90% CIs for the total treatment effect; P values for the total effects are P = 0.170 for HAZ and P = 0.302 for WHZ. Estimates for average total effects and CIs are taken from Table 4.

Fig. 4.

Estimated direct, indirect, and total effects of treatment on child growth over the course of the trial. The estimated indirect effect of vaccinating household chickens on child growth, through the effect on food intake, is the maroon solid line in each panel. The marginal monthly indirect effect is 0.0045 (P = 0.084) for HAZ and −0.0005 (P = 0.286) for WHZ (Table 4). These estimates are the slopes of the indirect effect lines in each panel. The maroon shaded triangles are 90% CIs for the indirect effects. Direct effects (blue dashed lines) and total effects (green dashed lines) are shown without CIs to limit visual complexity. The monthly total treatment effects are 0.0116 (P = 0.17) for HAZ and 0.0054 (P = 0.30) for WHZ, which are the slopes of the green dashed lines for HAZ and WHZ, respectively (Table 4). Fig. 3 provides a complementary perspective on the total treatment effect. Table 4 estimates are based on regression results presented in Tables 2 and 3.