Increased attacks in Borno State in December 2018 led to a massive population displacement. Subsequently, there were an increasing number of unvaccinated children who moved toward MMC and living in IDP camps in conditions favoring measles transmission. An ORI was essential for improving population immunity and interrupting the large measles outbreak in line with the global measles and rubella control and elimination goals [16].
The State has a history of outbreaks of measles in the last 5 years due to persistently low RI coverage, and has been conducting measles campaigns almost every 2 years as a key strategy for reaching high-risk populations in security challenge/hard-to-reach areas. In November 2015, Borno responded to a measles outbreak, and vaccinated a total of 837,743 children during the vaccination response. Only 66.7% of the targeted 1,255,100 children aged 6 to 59 months were vaccinated. In early 2017, a mass measles vaccination campaign was implemented as part of outbreak preparedness in conflict-affected areas of Borno state. The campaign was implemented in 25 LGAs of the State. According to the PCCS concluded in February 2018, the proportion of children aged 9 months to 59 months who received measles vaccine during the 2017 campaign was 72.2% and, of all respondents, only 52.2% had received measles vaccines before the campaign [17].
During the 2019 ORI, a total of 1,238,181 children were vaccinated with MCV giving an administrative coverage of 98.75%. As administrative coverage reports may not always be accurate, a PCCS was conducted and has indicated an aggregated weighted coverage for the 12 LGAs included in the survey of 85.7%. The 95% coverage objective was not achieved due to the complexity in conducting a vaccination campaign in an emergency setting where insecurity, regular influx of new persons, population displacement, and hard-to-reach areas are extensive. In order to overcome these obstacles, collaboration with the military enabled the vaccination teams to immunize eligible children in security compromised areas. This strategy builds upon the Reaching Inaccessible Children strategy (RIC) conducted by the military and the Reaching Every Settlement (RES) strategy which uses some military support to reach areas that were partially or completely inaccessible to the vaccination teams. [14]. In recently accessed territories at the time of the ORI (e.g., camps and communities in Bama, Gwoza, Dikwa, Damboa, Ngala, Kukawa and Monguno LGAs), “hit and run” vaccination activities have been conducted with military escort to provide immunization and basic health care in the camps in these areas. Additionally, in hard-to-reach settlements, the polio eradication platform was used to reach underserved communities with measles vaccination [18].
Data on measles VE estimations in emergency settings in Nigeria and other countries are limited, and, where available, quite dated. During a measles outbreak in refugee camps in Mozambican refugee camps in Malawi, VE was estimated for children less than 5 years using the screening method. The findings of this investigation showed a VE of more than 90% [19]. A two-stage cluster survey of 563 children in famine emergencies in Ethiopia found a low VE of 66.9% in children 9 − 36 months old. The authors suggested problems with the cold chain or vaccine administration [5]. We have obtained a high estimate of MCV VE among all age groups during ORI in Borno state Nigeria. VE ranged from 87.3% (95%CI: 71.0, 95.2) to 95.5% (95%CI: 98.3–99.9) for children from 9 to 71 months. Measles VE at 9–11 months and in greater than 12 months of age is expected to range between 84% and 92.5% [20].
Despite the limited storage capacity and poor immunization infrastructures at the lower level, efforts were made to ensure adequate cold chain and vaccine handling. Upon receipt of the MCV in-country, the vaccines were prepositioned in the Zonal cold store in Bauchi State (452 km driving distance to MMC). The vaccines and devices were distributed from the Zonal to the State store 2 weeks before the commencement of the ORI. The State distributed bundled vaccines to the LGA stores ahead of the campaign using cold boxes. Fast-cold chain was used to comply with the vaccine distribution process up to the communities and service delivery points.
This study is subject to some limitations. First, the result of the PCCS survey cannot be generalized to all children in the eligible age group in Borno state. The PCCS coverage results do not include coverage for children in the 14 LGAs that were not included in the survey since they were not part of the ORI and the additional LGA (Biu) dropped from the survey due to insecurity. The survey teams did not visit IDP camps and in addition, as a consequence of the ongoing insecurity, there has been constant displacement and migration of populations within and out of Borno state. The number of children eligible for vaccination at any settlement in Borno state is constantly changing and it is difficult to track movements and how the movements may affect the proportion of vaccinated and unvaccinated children. Secondly, the vaccination status of children in the inaccessible wards could not be estimated. The final limitation of the PCCS is the lag time of 4 months and 2 months between completion of the two phases of the campaign and timing of the survey. This may have influenced survey results as a consequence of recall bias. Only 32% of all interviewed individuals produced their vaccination cards, and 20% did not receive cards or could not recall whether they received vaccination cards. Considering multiple antigens delivered in the RI schedule and periodic ORI and preventive supplementary immunization activities, it is difficult for parents to accurately recall all doses of all antigens received by their child in the absence of widespread retention of vaccination cards.