Adult Males and Females in Osogbo, Osun State, Nigeria Manifest Extremely Low Level of Rubella Virus Susceptibility: Herd Immunity Implication

Abstract

Introduction: Despite the epidemic-prone nature of rubella and absence of its vaccine in routine immunization in Nigeria, there have been no reported cases of rubella outbreak in Osogbo, capital city of Osun State. We therefore hypothesized that susceptibility to rubella viral infection was low among males and females attending LAUTECH Teaching Hospital, Osogbo. Methodology: To verify this, 89 sera of consecutively selected consenting males and females in the General-Out-Patient Department of LAUTECH Teaching Hospital were tested for presence of protective level of anti-rubella virus IgG antibody using ELISA. Relevant socio-demographic/clinical data were obtained with interviewer-administered questionnaires. The serologic results were analyzed vis-à-vis the participants’ data. Results: The 89 participants were aged 3-85 years (mean age: 39.4 years) with 38.2% as males (mean age: 36.3 years). Overall rubella virus IgG seropositivity was 97.8%. Consequently, the rubella viral infection susceptibility rate was 2.2%, with group-specific susceptibility ranging from 0.0% to 4.2%. The susceptibility for males and females were 2.9% and 1.8% respectively. None of the participants’ variables was statistically associated with the susceptibility; this was mainly due to zero susceptibility of most groups of the participants. The 11 pregnant women and the 7 participants reporting skin rash had zero susceptibility to rubella. Conclusion: The study concludes that males, as well as females, had very low level of susceptibility suggestive of herd immunity against the virus which apparently was responsible for absence of rubella outbreaks in Osogbo, Osun State. As the high positivity rate indicated rubella endemicity, we recommend inclusion of rubella virus-containing immunization in national routine immunization for children and young adults, as well as, public enlightenment regarding rubella in Osogbo, Osun State.