Sero-epidemiology of rubella in Zambia in the pre-vaccination period (2005 – 2016) as baseline for evaluation of introduction of rubella vaccine into the national immunization program

Background Rubella is highly under-reported in Zambia as in most sub-Saharan countries despite being a disease of major public health concern especially among women of childbearing age. In September 2016, Zambia introduced a combined measles-rubella vaccine in children aged 0-14 years. In this study, we estimated the rubella sero-prevalence and its correlates between 2005 and 2016, a period prior to the introduction of Measles-Rubella vaccine in Zambia to provide baseline reference data for the future evaluation of its impact. Methods In a retrospective study, serum samples collected through the national measles surveillance program that tested negative for measles were examined for rubella IgM antibodies using the Siemens, Enzygnost® ELISA kit at the national measles laboratory accredited by WHO. Data on age, sex, province, year and month of onset were extracted from the surveillance data. Logistics regression analysis was conducted to determine independent predictors of rubella infection. Results Overall, a sero-prevalence of 29.2% (1313/4497) affecting mostly those between 5 and 24 years was determined. Logistics regression results indicated that only age, province, year and month were independently associated with rubella infection. The regional sero-prevalence varied from 21.8 – 37.3% peaking in the hot dry month of October. Logistics regression indicated that those in the age group 10-14 years (AOR=2.43; 95% CI [2.01 - 2.95]) were more likely while those aged <1 year less likely (AOR=0.31; 95% CI [021 - 0.48]) to have rubella compared to those aged 25 years or older. Persons in 2010 were less likely (AOR=0.12; CI [0.05, 0.28]) to have rubella infection compared to those in 2016. While rubella infections were more likely to occur between July and November compared to December, they were less likely to occur between February and May. Conclusions There is evidence that rubella virus was circulating in Zambia between 2005 and 2016 affecting more females than males and persons in the age group 5-24 years with a peak in the hot dry season. It is recommended that immunisation campaigns be targeted in months of lower virus transmission between February and May and in a situation of limited resources to those aged 5-24 years.