Long-term Rotarix™ vaccine effectiveness in coastal Kenya, estimated from child hospital admissions data from July 2014 to December 2022

Abstract Background Two doses of Rotarix™ demonstrated ∼64% effectiveness against rotavirus hospitalization in Kenyan children 2.5 years post-introduction. We evaluated long-term Rotarix™ effectiveness and monitored circulating genotypes over its 8.5 years of use in Kenya. Methods We conducted a test-negative case-control study in coastal Kenya among children admitted to Kilifi County Referral Hospital with diarrhea from July 2014 to December 2022. Eligible children had known Rotarix™ vaccination status, parent/guardian consent and rotavirus testing via ELISA. Positives were genotyped by sequencing. Rotarix™ effectiveness was estimated using unconditional logistic regression, adjusting for age, sex, calendar year, seasonality, and nutritional status. Results Of the 1,104 children (median age 12 months, interquartile range: 8–18) included in effectiveness analysis, 87% (962/1,104) had received 2 doses, 6% (70/1,104) 1 dose, and 7% (72/1,104) zero doses. Rotavirus was detected in stool specimens of 147 (13%) children. Overall, adjusted two dose Rotarix™ effectiveness was 68% (42–82%). Effectiveness in children ≤12 months was 83% (95% CI, 62–93%) compared to 38% (95% CI, -106–78%) in children >12 months. Genotyping of 147 positive samples revealed G3P[8] (66/147, 44.9%), G1P[8] (32/147, 21.8%), and G2P[4] (23/147, 15.6%) to be the most common circulating rotavirus genotypes during Rotarix™ vaccination era. Conclusions Rotarix™ maintained modest effectiveness in coastal Kenya during its 8.5 years of use. Effectiveness declined in the second year of life onwards probably reflecting a combination of both waning immunity and accumulation of natural immunity among unvaccinated children. Emergence of vaccine heterologous strains emphasizes need for continued effectiveness surveillance.