Rubella outbreak in a Rural Kenyan District, 2014: documenting the need for routine rubella immunization in Kenya

The prevention of birth defects has been identified as global health priority 1]. Birth defects or congenital anomalies are a significant cause of morbidity, disability
and mortality in many countries 2]–5]. Rubella infection has been identified as one of the leading causes of birth defects
globally 1].

Rubella, sometimes called German measles or three-day measles, is a contagious viral
disease. The infection is usually mild with fever and rash. However, maternal infection
during the first trimester of pregnancy can cause serious congenital malformations
in the fetus, a condition which is known as Congenital Rubella Syndrome (CRS) 6].

The annual incidence of CRS in developing countries is estimated to be 110,000 cases
per year, with a range of 14,000–308,000 7]. The most common manifestation of CRS is deafness. Eye defects including glaucoma
and retinopathy are common, and heart defects can also occur 8], 9].

The rubella vaccine contains a live attenuated (weakened) virus; immunization with
two doses is highly effective to prevent rubella 10], 11]. The ultimate goal of rubella vaccination is to prevent the occurrence of CRS 12]. The World Health Organization (WHO) currently advocates for the use of rubella-containing
vaccines (RCVs). RCVs are administered in monovalent form (rubella only) or in combinations
such as Measles-Rubella (MR) or Measles-Mumps-Rubella (MMR) 13]. By December 2009, 130 WHO member states including two of 46 WHO Africa region member
states used RCVs within their routine immunization systems 14].

Rubella vaccine is widely available through routine immunization programs in developed
countries. However is it is not available in many developing countries including Kenya
15]. National rubella immunization programs in the developed countries utilize one of
the following strategies: selective immunization of women, vaccination of infants,
or a combined strategy 16]. When an infant vaccination strategy is adopted, there is need for sustained high
coverage so as to ensure the susceptibility of adult women is not increased 17]. Although any of the three strategies could be used, it is important to include the
vaccination of women of childbearing age 18], 19]. The vaccine is delivered through routine immunization or Supplemental Immunization
Activities.

Rubella surveillance in Kenya is integrated within the national case-based measles
surveillance system. Through this system, approximately 400 rubella cases are confirmed
annually 20]. There is poor understanding of the burden of rubella infection and its prevalence
among pregnant women in Kenya. A few studies have sought to establish the burden of
rubella in Kenya. These studies, two in pregnant women and one in children were conducted
in diverse parts of the country 20]–22]. The study in pre-primary and primary school children identified an overall rubella
sero-positivity of 80 %, with the highest sero-positivity (94 %) detected among children
aged 14–20 years 20]. The studies in pregnant women showed that approximately 7 % were susceptible to
rubella infection 21], 22].

Although rubella cases are detected every year through the measles surveillance system,
a rubella outbreak in Kenya has not previously been described in the published literature.
In 2014, a rubella outbreak was reported in Njoro, a rural District in Rift Valley
Region of Kenya. We investigated the outbreak to determine its magnitude and describe
the outbreak in time, place and person. We also analyzed laboratory confirmed rubella
cases in the last 5 years (2010–2014) in order to fully define the burden of the disease
in the country.