Long-term impact of rotavirus vaccination on all-cause and rotavirus-specific gastroenteritis and strain distribution in Central Kenya: An 11-year interrupted time-series analysis

Background: Kenya introduced a monovalent rotavirus vaccine administered orally at 6 and 10 weeks of age into her National Immunization Program in July 2014. The study evaluated the long-term impact of the vaccine on hospitalization for all-cause and rotavirus-specific acute gastroenteritis (AGE) and strain epidemiology in Kenya. Methods: Data on all-cause and rotavirus-specific AGE and strain distribution were derived from an eleven-year hospital-based surveillance of AGE among children aged <5 years at Kiambu County Teaching and Referral Hospital (KCTRH) in Central Kenya between 2009 and 2020. Fecal samples were screened for group A rotavirus using ELISA and genotyped using multiplex semi-nested RT-PCR. Trends in all-cause and rotavirus-related AGE and strain distribution were compared between the pre-vaccine (July 2009–June 2014), early post-vaccine (July 2014–June 2016) and late post-vaccine (February 2019–October 2020) periods. Results: Rotavirus-specific AGE was detected at 27.5% (429/1546, 95% CI: 25.5–30.1%) in the pre-vaccine period; 13.8% (91/658, 95% CI: 11.3–16.6%) in the early post-vaccine period (July 2014–June 2016); and 12.0% (229/1916, 95% CI: 10.6–13.5%) in the late post-vaccine period (February 2019–October 2020). This amounted to a decline of 49.8% (95% CI: 34.6%–63.7%) in rotavirus-specific AGE in the early post-vaccine period and 53.4% (95% CI: 41.5–70.3%) in the late post-vaccine period when compared to the pre-vaccine period. All-cause AGE hospitalizations declined by 40.2% (95% CI: 30.8%–50.2%) and 75.3% (95% CI: 65.9–83.1%) in the early post-vaccine and late post-vaccine periods, respectively, when compared to the pre-vaccine period. G3P [8] was the predominant strain in the late post-vaccine period, replacing G1P[8] which had predominated in the pre-vaccine and early post-vaccine periods. Additionally, we detected considerable proportions of uncommon strains G3P[6] (4.8%) and G12P[6] (3.5%) in the post-vaccine era. Conclusion: Rotavirus vaccination has resulted in a significant decline in all-cause and rotavirus-specific AGE, and thus, provides strong evidence for public health policy makers in Kenya to support the sustained use of the rotavirus vaccine in routine immunization. However, the shift in strain dominance and age distribution of rotavirus AGE in the post-vaccine era underscores the need for continued surveillance to assess any possible vaccine-induced selective pressure that could diminish the vaccine effectiveness over time.