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 approximately 64% effectiveness against rotavirus hospitalization in Kenyan children 2.5 years postintroduction. 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 enzyme-linked immunosorbent assay. 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 1104 children (median age, 12 months [interquartile range, 8-18 months]) included in the effectiveness analysis, 87% (962/1104) had received 2 doses, 6% (70/1104) 1 dose, and 7% (72/1104) zero doses. Rotavirus was detected in stool specimens of 147 (13%) children. Overall, adjusted 2-dose Rotarix effectiveness was 68% (95% confidence interval [CI], 42%-82%). Effectiveness in children aged <12 months was 83% (95% CI, 62%-93%) compared to 38% (95% CI, -106% to 78%) in children aged ≥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 the 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 onward, probably reflecting a combination of both waning immunity and accumulation of natural immunity among unvaccinated children. Emergence of vaccine heterologous strains emphasizes the need for continued effectiveness surveillance.