Effectiveness of a monovalent human rotavirus vaccine among children of 5 years and under in KwaZulu-Natal.

Abstract

Human rotavirus infection is the leading cause of gastroenteritis in infants and young children worldwide. In South Africa, gastroenteritis is a major cause of childhood morbidity and mortality in children less than 5 years, and rotavirus infection has been documented as causing one-third of all gastroenteritis related hospital admissions. Vaccination is the major public health intervention to control rotavirus disease. The Rotarix® is the only rotavirus vaccine included in the national immunization program of South Africa. The effectiveness of this vaccine is questionable due to the continual outbreaks of rotavirus infection in South Africa, including KwaZulu-Natal, regardless of the high vaccination coverage. This study focused on evaluating the factors influencing the effectiveness of the Rotarix® vaccine in children 5 years and under in KwaZulu-Natal, South Africa. After obtaining written informed consent from parents or guardians, stool and blood specimens where collected from children 5 years and under presenting to King Edward VIII hospital (KEH VIII) in Durban, South Africa. The study was conducted between June 2014 and June 2015. Demographic and clinical information was collected using a well-structured questionnaire. Enzyme immunoassay (EIA) was performed to detect rotavirus antigen in the stool and rotavirus immunoglobulin G (IgG) in the serum. Selected EIA positive and negative samples were confirmed using G-types and P-types consensus primers in a Reverse Transcriptase Polymerase Chain Reaction (RT-PCR). The RT-PCR positives were genotyped using genotypes specific primers. The avidity of the rotavirus specific IgG was determined using the urea elution technique. Rotarix® vaccines stored at optimum temperatures were collected from the provincial pharmaceutical store. The effect of sub-optimal temperatures on the potency of the Rotarix® vaccine were determined using the plaque assay. Three hundred and sixty-five (365) stool specimens were collected. Rotavirus antigen was detected in 83 (22.7%) patients from stool specimens. The stratification of rotavirus cases by vaccination status was not significant (p=0.4). The distribution of rotavirus was not significantly associated with HIV status of the children (p=0.7). We observed that seasonality was a significant driving force influencing the prevalence of rotavirus infection in our setting (p<0.001). We recorded the highest rotavirus prevalence in the winter months of the year with 79 (45.9%) positive cases of rotavirus associated diarrhoea. Blood specimens were only collected in 35 patients. From the corresponding stool specimens [21 (60%) EIA positives and 14 (40%) EIA negatives)], 29 (82.9%) were positive for rotavirus using conventional RT-PCR. Genotyping revealed G9P[8] (20.7%) to be the most prevalent genotype followed by G9P[4] (13.8%), G12P[4] (10.3%), G9P[6] (6.9%) and a 3.4% prevalence was recorded for each of G4/G8P[6], G4P[6], G12P[6], G8P[10] and G9P[10]. We were unable to fully genotype some of the rotavirus strains

(non-typeable) by the available primers. 2 (6.9%) and 4 (13.8%) were non-typeable for the G and P types respectively. However, all 35 serum samples were positive for rotavirus IgG. We observed that the rotavirus specific IgG had no significant effect on the prevalence of rotavirus detection in stool (p=0.8). There was no significant difference in the mean avidity of IgG in the 3 vaccination strata (p=0.3). Exposure of the Rotarix® vaccine to the seasonal temperatures and to extreme temperatures of 40oC for 3 to 72 hours as well as -20oC and -80oC for 12 hours did not affect the potency of the vaccine beyond its expected standard. Our study highlighted the genetic diversity of rotaviruses and poor immunogenicity of the vaccine as key factors affecting the effectiveness of the rotavirus vaccine. Whether the vaccine is able to induce homotypic and heterotypic protection in immunized children is critical in predicting the long range effectiveness of this vaccine against uncommon regional rotavirus strains. Interventions targeted at improving socio-economic conditions in low income countries might be a starting point towards the control and prevention of rotavirus infection in these settings.