Zambia recently introduced routine infant immunization against rotavirus - the most important cause of severe gastroenteritis and diarrhoea mortality in children. Although vaccines like Rotarix are a cost effective tool against infectious diseases, live oral vaccines can be less immunogenic and efficacious in developing world settings as compared with industrialized countries. Reasons behind this phenomenon are not well understood, but may relate to continued maternal antigen exposure and high level maternal immunity that is passed to the foetus/newborn transplacentally and/or through breast milk. Therefore, three arising hypotheses include: (i) high-level rotavirus-specific maternal immunity (in the form of anti-rotavirus breast-milk immunoglobulin A (IgA) and transplacental serum IgG) is a major contributor to failed seroconversion following infant vaccination. (ii) Malnutrition negatively impacts infant immunity and increases the risk of post-vaccination rotavirus gastroenteritis. (iii) Introduction of rotavirus vaccine will alter the molecular epidemiology of circulating rotavirus strains detected in vaccinated children presenting with severe diarrhea. To address these hypotheses, the proposed study will recruit a prospective cohort of 420 mother-infant pairs. These will be enrolled at the time of vaccination and followed for up to four years. Baseline immunological status will be ascertained and seroconversion rates determined a month after full immunization. Incident rotavirus gastroenteritis will be monitored in the vaccinated infants whenever episodes of diarrhoea occur; through this surveillance, the sero-strains of rotaviruses causing disease will be tracked over the four year period. Contributions of HIV infection both in mothers and infants, vitamin A and zinc deficiency, weight for age Z-scores as well as mid upper arm circumference will also be assessed. Knowledge gained from this study will inform future interventional trials on strategies to improve rotavirus vaccine effectiveness in the developing world.
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Proportion of Immunized Infants Exposed to High Breast Milk Anti-rotavirus Immunoglobulin-A Who Fail to Seroconvert
Timeframe: 1 month following full immunization
Proportion of Immunized Infants Exposed to Transplacentally-acquired, Rotavirus-specific, Infant Serum IgG Who Fail to Sero-convert.
Timeframe: 1 month after full immunisation
Proportion of Immunized Infants Exposed to Maternal HIV Infection Who Fail to Seroconvert
Timeframe: 1 month after the two vaccine doses