The impact of declining vaccination coverage on measles control: a case study of Abia state Nigeria

Introduction Efforts at immunizing children against measles was intensified in Nigeria with nation-wide measles vaccination campaigns in 2005 - 2006, 2008 and 2011 targeting children between 9 and 59 months. However, there were measles outbreaks in 2010 and 2011in Abia state Nigeria. This study seeks to find out if there is any association between measles immunization coverage and measles outbreak. Methods This is a descriptive analysis of the 2007 to 2011 Abia state measles case-based surveillance data supplied to Abia state World Health Organization office and Abia State Ministry of Health by the disease surveillance and notification officers. Results As the proportion of cases with febrile rash who were immunized decreased from 81% in 2007 to 42% in 2011, the laboratory confirmed cases of measles increased from two in 2007 to 53 in 2011.Of the laboratory confirmed cases of measles, five (7%) occurred in children < 9 months, 48 (64%) occurred in children 9 - 59 months and 22 (29%) occurred in children < 59 months old. Seventy five percent of all laboratory confirmed cases of measles occurred in rural areas. Conclusion Efforts should be made to increase measles immunization in children between 9 and 59 months as most cases of measles occurred in this age group as immunization coverage dropped. In addition, further studies should be carried out to determine the cause of the disproportional incidence of measles in rural areas in Abia state bearing in mind that measles immunization coverage in urban and rural areas was not markedly different


Introduction
Measles is a highly infectious disease that is transferred from one person to another through aerosolized droplets or by direct contact with the nasal and throat secretions of infected persons [1]. Measles transmission is prevented by vaccination and in sub-Saharan Africa, it is recommended that the vaccine be given at 9 months of age, by which time the child would have lost passive immunity conferred by maternal antibodies. One dose of measles vaccine confers life-long immunity to approximately 85% of those vaccinated [1]. Childhood immunization programs targeted at children less than 59 months have led to a marked decrease in measles infections and outbreaks [2]. However, in order to interrupt the endemic transmission of measles virus; a population immunity of ≥95% has to be achieved [2].
Measles case fatality is estimated to be between 3 to 5% in developing countries and may be as high as 10% during epidemics [1]. Despite the efforts made at increasing immunization, measles remain a leading cause of under-five mortality in Africa [3].There were 139, 300 measles deaths globally in 2010 which represents nearly 380 deaths every day or 15 deaths every hour [4]. Nigeria is one of the 45 countries that together account for 94 percent of the global deaths caused by measles [5].
Measles-case based surveillance is a system put in place to detect cases and outbreaks of measles. It involves reporting and investigating any suspected case of measles and to use the data to evaluate immunization efforts and predict outbreaks through the identification of geographical areas and age groups at risk [1]. In 2006, measles case based surveillance was established in Nigeria using the resources and infrastructure of the already established surveillance for Acute Flaccid Paralysis (AFP). It involves both passive and active surveillance [2,3].
In 2008, the WHO African regionaloffice set aregional preelimination goal to be achieved by the end of 2012. The goals include (1) reducing the incidence of measles to < 5 cases/ 10 6 population per year in all countries, (2) increasing the first dose ofmeasles containing vaccine (MCV1) to greater than 90% at the national level and greater than 80% in all districts and (3) measles surveillance system performance that reports non-measles febrile rash illness rate of ≥2 cases per 100,000 population per year [6].

Abia State information
Abia state is in the south-eastern part of Nigeria and covers a land area of 5,243.7 square kilometers. The population of Abia State by the 2006 population census was 2,833,999 and with an annual growth rate of 2.7%, the estimated population in 2011 is 3,278,699.
It has 17 local governments [7,8]. About 70% of the population lives in rural areas. The state has a high burden of a young population with children aged 0-14 years accounting for 36.8% of the population. There is also a high age dependency ratio of 66.5%.
Over 59% of the population is estimated to live below the poverty line of one US dollar a day [8]. This study analyzes measles case prior to the collection of serum sample is not considered to be a laboratory confirmed case of measles but as a case ofIgM positivity secondary to measles immunization [1,2].
Page number not for citation purposes 3 A confirmed outbreak of measles is defined as 3 or more measles IgM positive (laboratory confirmed) cases in a health facility or district in one month [9]. Measles incidence per 100,000 population was calculated by dividing the number of reported measles cases by the population (based on the 2006 census) and multiplied by 100,000. Data was analyzed using SAS 9.1.

Results
From Table 1 The analysis of the age of the cases with febrile rash showed that on average over the five years; approximately 50 percent of the cases with febrile rash were within 9 and 59 months. 8% were less than 9 months and the remaining 42% were above 59 months. 64% of confirmed cases of measles between 2007 and 2011 were between 9 and 59 months. 7% were below 9 months and 29% were above 59 months ( Table 1).
About 80% of cases with febrile rash reside in the rural areas while about 75% of those with laboratory confirmed cases of measles reside in the rural area ( Table 1 and Table 2).  Table 1).
On average, between 2007 and 2011, 34% of cases with febrile rash living in urban areas were unimmunized while 41% of those living in rural areas were unimmunized. In 2007, 25% of febrile rash cases living in urban areas and 16% of those living in rural areas were unimmunized while in 2011, 49% of those living in urban areas and 60% of those living in rural areas were not immunized ( Table 1). .
Over the five years under review, for cases with confirmed cases of measles, 61.33% of them were unimmunized while 87% of the confirmed cases of measles occurred during the dry season ( Table   2). The peak of measles infection occurred in January and February which accounted for 55% of all cases ( Table 3).

Discussion
As the measles vaccination in 9 -59 months old dropped from The result showed that 39.23% of those who had febrile rash between 2007 and 2011 were not immunized. This is low compared to the national average of 59% [9]. 61.33% of the laboratory confirmed cases of measles were not immunized compared to the Nigerian average of 71.2% [9].
Similarly, the proportion of those with febrile rash immunized .Failure to maintain high coverage of childhood immunization in all districts has been noted to lead to the resurgence of measles [6,12].
About 75% of the measles cases occurred in rural areas. Although the average unimmunized rate for the 5 years for urban areas (34%) is not very different from those in the rural areas (41%), there was a wide discrepancy in the rate of cases in urban and rural areas. This discrepancy might be explained by the fact that more people live in rural areas than urban areas. However, another reason might be that children in rural areas are poorer, more malnourished and more susceptible to infection [5]. This means that more efforts in immunization should be concentrated in rural areas.
Most of the cases of measles occurred in the dry season, with the peak in January and February. This is in conformity with earlier observed trend of measles infection [12]. However, in a study in Niger, the cases of measles started in September, increased progressively and peaked in March [13].

Conclusion
Decline in routine childhood measles immunization could have led to the resurgence of measles in Abia state after the state was measlesfree for more than 12 months. Furthermore, most cases of measles occur in children between 9 and 59 months and most cases of measles occur in rural areas. Efforts should be made to increase measles immunization in children between 9 and 59 months. Due to the peak incidence of measles in the dry season vaccination campaigns should be increased towards the end of the rainy season  Tables   Table 1: Demographics of cases with rash