We found that measles cases and reporting rates have been increased in Addis Ababa city from 2005 to 2014. The reporting rate was increased to topmost in 2010 followed by in 2014 and 2013. Corresponding to the increment of the reporting rate, non-measles rash illness rate was also increased by two folds. The increment of the non-measles febrile rash illness rate is an indicator for the sensitivity of the surveillance system. We believe that the increment of the cases and reporting rate of measles observed might be attributed to the sensitivity of surveillance system. The reporting or non-measles febrile rash illness rate was found to be greater than minimum WHO requirement which ≥2 per 100,000 per year [18, 19] which indicates that the measles surveillance system is sensitive in the capital. In addition, prolonged outbreak between 2013 and 2014 significantly increases measles reporting rate (Fig. 2). We also believe that increment of the reporting rate was might be also attributed to unvaccinated children over years. We have also observed that, reporting rate of measles was relatively low in July and August and start increasing from September over years. This is coexistence with school closure in July and August and reopening in September which might be contributing risk factors. Evidence from other study demonstrated a clear peak in transmission of measles which is coinciding with the start of the school calendar and decrease during vacation [21].
The study revealed that, the CFR is lesser as compared with other studies in Africa [22, 23]. The comprehensive community based study by WHO indicated that the CFR in Sudan, Ethiopia, Kenya and Tanzania ranged from 3 to 4% [24] which is much higher. The lower the case fatality rate in this finding might be attributed with the improvement of early case detection, clinical treatment and access to health care deliveries in Addis Ababa which needs further investigation.
The analysis showed that, all age groups were affected having median age 5 and Interquartile age range 2–18 years. The study conducted in Malawi on measles outbreak indicates that Median age of case-patients was 7 years (Interquartile range 1–16) which supported our finding [25]. Our finding further revealed that the reporting rate was high in lower age groups. Infants < 1 year of age were mostly affected (40/100,000) followed by children 1–4 years (11/100,000), 5–14 years (6/100,000), 15–44 Years (4/100,000) and 45+ years (0.3/100,000). The previous study in Addis Ababa indicates that the Seronegative prevalence decreased from 66% in infants less than 9 months of age to 20.4% in 9–59 month old, 4.9% in 5–14 years old, and 0.7% in adults (15–49 years) which supported our finding [26]. We observed that the trends in measles reporting rate in different age groups over years was follow similar trend. We did not observed shift over time in age groups. In each year infants under five were mostly affected (Fig. 3).
In our analysis, we found that 24% of the measles cases were not received measles vaccine while the vaccination status of significant portion, 54%, of the cases were not known. Furthermore, from the laboratory confirmed measles cases again 24% were not vaccinated and the vaccination status of 62% were not known (Table 4). This suggests that, there is some gaps in routine vaccination coverage. Even in the areas where the vaccination coverage at 9th month is 100%, the effectiveness of measles vaccine is only 85% with single dose [27, 28]. In Ethiopia 1st dose measles vaccine has given at the age of 9 months [13] whereas there is no 2nd dose routine vaccination schedule. The second opportunity is only through supplementary immunization activities. In this finding, from all laboratory confirmed cases, only 2% received two and more disease of measles vaccine.
We believe that, there are sufficient health facilities with better health care deliveries including vaccination services are available in Addis Ababa as compared with other areas of the country. However, the increment of the reporting rate and occurrences of measles outbreak in Addis Ababa city indicates that the vaccination activities and other measles prevention and control interventions has limitation in the capital.
This study on retrospective measles surveillance data has some limitations. As we used secondary surveillance data, we could not have mentioned how vaccination status of cases were obtained. Hence, vaccination status of the cases was not validated. The number of measles cases and its epi-classification used in this study was based on available surveillance data which might be less representative because of lack of sensitivity of measles surveillance. Contributing risk factors for not vaccinating children in Addis Ababa were also not determined as risk determinants were not available in the data. Vaccine cold chain quality was also not accessed as we used secondary surveillance data.