Long-term Rotarix Vaccine Effectiveness in Coastal Kenya, Estimated From Child Hospital Admissions Data From July 2014 to December 2022.

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.