Acute rotavirus infection is associated with the induction of circulating memory CD4+ T cell subsets.

Strong CD4+ T cell-mediated immune protection following rotavirus infection has been observed in animal models, but its relevance in humans remains unclear. Here, we characterized acute and convalescent CD4+ T cell responses in children who were hospitalized with rotavirus-positive and rotavirus-negative diarrhoea in Blantyre, Malawi. Children presenting with laboratory-confirmed rotavirus infection had higher proportions of effector and central memory T helper 2 cells during acute infection i.e., at disease presentation compared to convalescence, 28 days post-infection defined by a follow-up 28 days after acute infection. However, circulating cytokine-producing (IFN-γ and/or TNF-α) rotavirus-specific VP6-specific CD4+ T cells were rarely detectable in children with rotavirus infection at both acute and convalescent stages. Moreover, following whole blood mitogenic stimulation, the responding CD4+ T cells were predominantly non-cytokine producers of IFN-γ and/or TNF-α. Our findings demonstrate limited induction of anti-viral IFN-γ and/or TNF-α-producing CD4+ T cells in rotavirus-vaccinated Malawian children following the development of laboratory-confirmed rotavirus infection.

Comparative whole genome analysis reveals re-emergence of human Wa-like and DS-1-like G3 rotaviruses after Rotarix vaccine introduction in Malawi.

G3 rotaviruses rank among the most common rotavirus strains worldwide in humans and animals. However, despite a robust long-term rotavirus surveillance system from 1997 at Queen Elizabeth Central Hospital in Blantyre, Malawi, these strains were only detected from 1997 to 1999 and then disappeared and re-emerged in 2017, 5 years after the introduction of the Rotarix rotavirus vaccine. Here, we analysed representative twenty-seven whole genome sequences (G3P[4], n = 20; G3P[6], n = 1; and G3P[8], n = 6) randomly selected each month between November 2017 and August 2019 to understand how G3 strains re-emerged in Malawi. We found four genotype constellations that were associated with the emergent G3 strains and co-circulated in Malawi post-Rotarix vaccine introduction: G3P[4] and G3P[6] strains with the DS-1-like genetic backbone genes (G3-P[4]-I2-R2-C2-M2-A2-N2-T2-E2-H2 and G3-P[6]-I2-R2-C2-M2-A2-N2-T2-E2-H2), G3P[8] strains with the Wa-like genetic backbone genes (G3-P[8]-I1-R1-C1-M1-A1-N1-T1-E1-H1), and reassortant G3P[4] strains consisting of the DS-1-like genetic backbone genes and a Wa-like NSP2 (N1) gene (G3-P[4]-I2-R2-C2-M2-A2-N1-T2-E2-H2). Time-resolved phylogenetic trees demonstrated that the most recent common ancestor for each ribonucleic acid (RNA) segment of the emergent G3 strains was between 1996 and 2012, possibly through introductions from outside the country due to the limited genetic similarity with G3 strains which circulated before their disappearance in the late 1990s. Further genomic analysis revealed that the reassortant DS-1-like G3P[4] strains acquired a Wa-like NSP2 genome segment (N1 genotype) through intergenogroup reassortment; an artiodactyl-like VP3 through intergenogroup interspecies reassortment; and VP6, NSP1, and NSP4 segments through intragenogroup reassortment likely before importation into Malawi. Additionally, the emergent G3 strains contain amino acid substitutions within the antigenic regions of the VP4 proteins which could potentially impact the binding of rotavirus vaccine-induced antibodies. Altogether, our findings show that multiple strains with either Wa-like or DS-1-like genotype constellations have driven the re-emergence of G3 strains. The findings also highlight the role of human mobility and genome reassortment events in the cross-border dissemination and evolution of rotavirus strains in Malawi necessitating the need for long-term genomic surveillance of rotavirus in high disease-burden settings to inform disease prevention and control.