Abstract
BackgroundIn rural Gambia, rates of malnutrition and infection are higher during the annual rainy/‘hungry’ season (June–October) in comparison to the dry/‘harvest’ season (November–May). The effects of this seasonal pattern on an infant’s immune development and their capacity to respond to childhood vaccinations remain unclear. The aim of the current analysis was to determine whether antibody responses to diphtheria-tetanus-pertussis (DTP) vaccinations in infants differ between seasons.MethodsInfants received the DTP vaccine at 8, 12 and 16 weeks of age and antibody titres were measured in blood samples collected at 12 (n = 710) and 24 (n = 662) weeks of age. Mean DTP antibody titres, adjusted for maternal and infant confounders, were compared by t-tests and the effect sizes of the mean differences were calculated between seasons at mid-gestation (20 weeks gestation) and first vaccination (8 weeks of infant age).ResultsA smaller number of infants received their first vaccination during the rainy/hungry season months compared to the dry/harvest season (n = 224 vs. n = 486). At 12 weeks, infants vaccinated during the rainy/hungry season had lower weight-for-length Z-scores (p = 0.01) and were more likely to be anaemic (p < 0.001). Their mothers, however, were pregnant mostly during the dry/harvest season, had higher weight gain (p < 0.001) and were less likely to be anaemic during pregnancy (p < 0.001). At 12 weeks, infants vaccinated during the rainy/hungry season had significantly higher mean diphtheria, tetanus and pertussis antibody titres; by 62.3, 16.9 and 19.7%, respectively (all, p < 0.001). However, at 24 weeks, they had lower mean anti-diphtheria titres (by 20.6%, p < 0.001) compared with infants vaccinated during the dry/harvest season, and no differences were observed in mean tetanus and pertussis antibody titres by vaccination season.ConclusionsInfant antibody response to the primary dose of the DTP vaccine was influenced by both season of pregnancy and infancy, although effects were diminished following three doses. Environmental exposures, including nutrition, to both the mother and infant are hypothesised as likely drivers of these seasonal effects.
Highlights
In rural Gambia, rates of malnutrition and infection are higher during the annual rainy/‘hungry’ season (June–October) in comparison to the dry/‘harvest’ season (November–May)
All mothers of infants vaccinated during the rainy/hungry season were at mid-gestation (20 weeks gestation) in the dry/harvest season compared with less than a quarter of mothers of infants vaccinated during the dry/harvest season (100% vs 22.8%, p < 0.001)
Mothers of infants vaccinated during the rainy/hungry season had higher haemoglobin levels and were less likely to be anaemic at enrolment, 20 or 30 weeks gestation compared with mothers of infants vaccinated during the dry season
Summary
In rural Gambia, rates of malnutrition and infection are higher during the annual rainy/‘hungry’ season (June–October) in comparison to the dry/‘harvest’ season (November–May). In subSaharan Africa, two-thirds of the population, representing 645 million people in 2018, live in rural areas and rely predominantly on subsistence farming for their livelihood (World Bank) In this setting, rainfed agriculture accounts for 95% of food production and low harvests, alongside poor long-term storage for perishable food products, put many subsistence farming households at risk from a seasonal cycle of poverty and hunger [9]. Women are especially vulnerable to this seasonal pattern as they contribute to the agricultural labour force and continue to endure intensive physical activity during pregnancy and lactation [9] This results in a negative energy balance [28] and leads to a higher prevalence of low birth weight infants, iron deficiency anaemia and maternal and child morbidity and mortality, primarily from infections, during the rainy season months [3, 29]
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