Rotavirus prevalence and seasonal distribution post vaccine introduction in Nairobi county Kenya

Rotaviruses are one of the leading etiological agents of gastroenteritis in young children, for which a monovalent G1P(8) vaccine has been provided for free in Kenyan since July 2014. The main objective was to estimate the post vaccine prevalence and seasonal distribution of rotavirus diarrhea in children less than 5 years in Nairobi County, Kenya. Rotavirus positive samples were collected from children below 5 years of age in two hospitals within Nairobi County where vaccination status was card-confirmed. The children were examined and the demographic and clinical profiles of the children were recorded. Fecal specimens were analyzed for rotavirus antigen using an ELISA kit, followed by characterization by PAGE. Out of the total 323 samples, 49 had detectable rotavirus infection, representing 15.2% prevalence. Age distribution of rotavirus prevalence was as follows: ≤ 6 months-8.5%, 7-12 months-27.4%, 13-24 months - 41.4%, 25-36 months - 16.4% while 36-65 months had 6.3%. Rotavirus diarrhea was more common in wet and cold months of the year, the highest prevalence being observed in August (24.5%), 12.3% in both July and March, while April scored a prevalence of 10.2%. Out of the 49 rotavirus positive children, 48 had vomiting and abdominal cramps while all had fever and watery stool. The prevalence of Rotaviral diarrhea in children less than 5 years in Nairobi County Kenya has greatly reduced following the vaccine introduction and is more common during the wet and cold seasons of the year.


Introduction
The World Health Organization (WHO) estimate that almost 2.5 billion episodes of diarrhea occur annually in children <5 years of age in developing countries [1]. More than 80% of these episodes occur in Africa and South Asia, 46% and 38%, respectively [2]. Rotavirus remains the leading etiology of severe and fatal diarrhea worldwide, responsible for approximately 40% of diarrheal deaths [3]. However, the introduction of rotavirus vaccines is believed to have a substantial impact on the burden of rotavirus diarrhea [4], with the majority of the impact seen by the third year after introduction [5]. Two oral live attenuated rotavirus vaccines (Rotarix and RotaTeq) have been licensed and introduced since 2006 [6]. Rotarix (GlaxoSmithKline) is a monovalent G1P [8] rotavirus vaccine (RV1) derived from a human rotavirus strain by serial passage in cell culture [7] while RotaTeq (Merck) is a pentavalent human-bovine (WC3) reassortant vaccine, with the five most common human type specificities G1, G2, G3, G4 and P [8], expressed individually on the genetic backbone of a bovine rotavirus strain naturally attenuated for humans [8]. The vaccine in use is administered orally to infants at 6 and 10 weeks of age globally, although different countries use different schedules [9]. As of May 1 st 2016, rotavirus vaccinations had been implemented in the national immunization programs of 81 countries, including 38 low-income countries being supported by the Global Alliance for Vaccines Initiative (GAVI) Alliance [10]. Before the vaccine introduction in Kenya, rotavirus group A (RVA) was estimated to cause more than 3,908 deaths, 3,015 outpatient visits, and 279 hospitalizations per 100,000 children <5 years of age annually. The cost to the health care system amounted to US$10.8 million annually [10]. With support from GAVI, Kenya introduced the two-dose RV1 into her national immunization programme in July 2014. The vaccine is administered orally at 6 and 10 weeks of age and the goal is to protect more than 1.5 million children in the country from developing severe acute gastroenteritis [10]. Since vaccine introduction, information on the actual impact of rotavirus vaccinations in preventing and reducing the health burden of severe childhood diarrhea in Kenya is limited. More so, an indication that the vaccines are much less efficacious in some low-income countries [11] underscores the importance of monitoring the impact of rotavirus vaccinations in low income settings during routine programmatic use, where the actual performance of a vaccine may differ from the optimal conditions of clinical trials. Hence, in this study, we report on the impact of rotavirus vaccination on the prevalence, age and seasonal distribution of rotavirus-specific gastroenteritis in urban population in Nairobi County, Kenya, three years after the introduction of the vaccine into the national immunization programme.   P=0.0281) ( Table 3).

Case study
Clinical symptoms the major clinical symptoms related to rotavirus infections were mainly watery stool/diarrhea, vomiting, abdominal cramps, and fever. All the children under study had watery diarrhea and fever, while 98% experienced vomiting and abdominal pains.
Page number not for citation purposes 4

Discussion
Reviews of rotavirus research conducted in Kenya before the vaccine introduction reveal rotavirus prevalence ranging from 6% to 56% in children aged below 5 years [14,15]. In Nairobi County, a rotavirus prevalence of 24% was registered in children <5 years of age before the vaccine introduction [16]. 49% following the nationwide vaccine use [17]. The decline only occurred in children <1 year of age who were eligible for vaccination and was greatest during the rotavirus season months, supporting that it was associated with vaccine implementation [18]. In Kenya, a study conducted in the Western parts of the country revealed a 48% decline in the rotavirus related hospitalizations among children aged <5 years in the post-vaccine period [10].
In another study conducted in the peri-urban children of Central Kenya between 2014 and 2016 [17], an approximately 50% reduction in the rate of RVA gastroenteritis among children aged <5 years was observed, which was a slightly higher reduction compared to the 35% reduction registered in our study. This could have been due to the fact that our study captured low income urban setups of Nairobi County

Competing interests
The authors declare no competing interests.