Correspondence Email: [email protected].
Background: The measles virus causes an infectious disease. The introduction of mass vaccination efforts in the 1960s resulted in a considerable reduction in global measles mortality. Thus, the goal of this study is to characterise the epidemiology of measles infection in Bayelsa State, Nigeria, two (2) to twelve (12) months after the state's measles vaccine campaign.
Method: A descriptive cross-sectional study was conducted, using secondary data analysis of case-based surveillance data from the State’s ministry of health IDSR001C from January to December 2022. Suspected and confirmed cases of measles were defined according to the World Health Organization (WHO) standard case definition, vaccination campaign report for the measles campaign conducted in November, 2021 was also analyzed.
Findings: A total of 450 suspected measles cases were reported from January to December, 2022, out of which 151 were laboratory confirmed (IgM+), giving a case positivity rate (PR) of 34%, also 1 death in confirm case with case fatality rate (CFR) of 0.7%. Male Positive cases were 51%, and 45.7% of the positive cases were under-fives. The frequency of distribution of the 151 confirmed cases according to LGAs was; Yenagoa-56 (37.1%); Southern Ijaw-32 (21.20%); Ekeremor-24 (15.9%); Ogbia-19 (12.6%); Sagbama-8 (5.2%); Brass-10 (6.6%); and Kolokuma-Opokuma-2 (1.3%). Vaccine coverage in the November 2021 measles campaign in Bayelsa state was 86%.
Conclusion: Despite immunisation programmes with an 86% vaccination coverage, Bayelsa state in Nigeria recorded 14 measles outbreaks in six local government areas (LGAs) from January to December 2022. Routine immunisation, augmented by planned campaigns every 2-5 years, remains the foundation of modern measles control and elimination efforts. Even when management methods appear to be working, big, unexpected outbreaks continue to occur. Supplementing these operations with mass vaccination campaigns initiated when low levels of measles immunity are detected in a population sample (i.e., serosurveys) or incident measles cases arise may give a strategy to restrict the magnitude of outbreaks.
Keywords: Epidemiology, Description, Measles, Morbidity, Mortality.
Outbreaks of measles continue to be a public health issue in Africa and other underdeveloped countries across the world. Measles case mortality rates in developing nations are believed to be between 3 and 5%, with rates as high as 10% during outbreaks [1, 2]. Despite efforts to increase immunisation, measles remains a leading cause of death among children under the age of five in Africa [3, 4]. In 2011, there were approximately 139,300 measles deaths worldwide, representing nearly 380 deaths per day or 15 deaths per hour [5, 6]. Nigeria, along with other developing nations, currently responsible for around 94% of global measles mortality each year [7, 8]. Despite the availability of a low-cost, safe, and highly effective vaccine, measles continues to be a major cause of childhood death and morbidity in many parts of the world [3, 9]. The World Health Organisation (WHO) estimated that measles caused 875 000 fatalities worldwide in 1999, with more than half of these deaths occurring in Africa . The WHO has recommended a strategy that includes improving measles vaccination coverage as well as providing a second opportunity for measles immunisation to all children, either through a second routine dose or through periodic supplementary immunisation activities (SIAs) . Table 1 below, for example, summarises measles SIAs undertaken between 2005 and 2022. These SIAs often start with a 'catch-up' SIA aimed at children aged 9 months to 14 years, followed by periodic 'follow-up' SIAs aimed at children aged 9 to 59 months . While novel and emerging illnesses continue to emerge over the world, they have a considerable impact on global health security [13-20]. In recent years, Nigeria has seen multiple measles outbreaks, owing mostly to inadequate regular immunisation (RI) coverage. Vaccination has significantly reduced measles-related morbidity and mortality worldwide in 2019, but measles remains a global public health concern due to its highly transmissible nature, proclivity to rapidly develop into outbreaks among children in Dutch disease settings, and rising levels of vaccine hesitancy [20-22]. Measles, on the other hand, is an infectious disease caused by the measles virus . Millions of people died each year from measles infection prior to the introduction of vaccines. The introduction of mass vaccination efforts in the 1960s resulted in a considerable reduction in global measles mortality [24, 25]. Measles can be passed from person to person by aerosolized droplets or direct contact with secretions from infected people's noses and throats [26, 27]. Individuals who have not been immunised are more likely to develop measles. Malnourished children are more prone to develop complications and die from measles infection [25, 26]. Despite significant advances, including 56 million deaths saved globally by vaccination from 2000 to 2021, measles killed approximately 130,000 people (mainly children) in 2021 . The lack of endemic measles cases for a period of twelve months or longer, in the context of sufficient surveillance, and when the following criteria are met, is classified by WHO as measles eradication: (i) achieving and maintaining at least 95% coverage with both first dose measles vaccination and the second opportunity of measles vaccination in all districts and nationally; (ii) having less than 10 confirmed cases in 80% or more of measles outbreaks; (iii) achieving a measles incidence of <1 confirmed measles case per million population per year . Over 115,500 cases of measles were reported in 2021 in Africa . About 125 million preschool-aged children in Africa are vitamin A deficient, putting them at a high risk of passing away, contracting a serious infection, or going blind from measles . WHO Nigeria, in collaboration with other partners, planned and carried out a measles campaign (supplemental immunisation activity) in 13 states between November and December 2021. The initiative achieved 96.4% administrative coverage (WHO, 2021). Supplemental Immunisation Activities (SIAs) are vaccination techniques that are intended to reach people who have not been vaccinated through conventional services . They are also used to rapidly immunise susceptible people, assisting the population in achieving "herd" immunity and halting disease transmission [15-18, 29]. SIAs are critical for reaching underserved groups and increasing overall immunisation coverage [3, 16, 17, 20].
While measles is an endemic disease in Nigeria, outbreaks occur on a regular basis. Nigeria has one of the highest rates of measles in the world. In 2021, a total of 10,096 confirmed cases and 109 deaths were reported across 33 states and the FCT [1, 30-32]. Children under five years were 7,573(75.0%) out of the confirm cases reported . In Bayelsa state, measles infection occurs all-year round with children less than 5 years being the most affected . Bayelsa state conducted an immunization campaign for measles in 2021. Hence, the aim of this study is to reduce the pool of susceptible individuals and maintain Rt < 1 and to describe the epidemiologic characteristics of measles outbreak in 2022 in Bayelsa, South-South Nigeria and also the association between IgM results of measles suspected cases with vaccine coverage in the November 2021 measles campaign. Targeted vaccination coverage for measles containing vaccine (MCV) in order to achieve herd immunity and eventual measles elimination, a goal of the World Health Organization (WHO) Regional Office for Africa since 2012, is generally estimated at 95%.
Bayelsa State is located in the South-South geopolitical zone (see fig 1 below), in the central Niger Delta region of Nigeria and it is featured in many studies [34-43]. It is mostly lowland, swamps, marshlands and tropical rainforest [40-43]. There is significant rainfall throughout the year with peaks between April and October [34-39]. The average monthly temperature range is 25°C and 31°C, with the hottest months being December to April. The state experiences high relative humidity throughout the year, with a modest decline during the dry season. The state is made up of eight LGAs namely; Brass, Ekeremor, Nembe, Ogbia, Kolokuma/Opokuma, Sagbama, Southern-Ijaw and Yenagoa [37-41].
A cross sectional descriptive study was conducted among all measles cases reported in Bayelsa from January to December 2022.
Measles reporting is done through the integrated disease surveillance and response (IDSR) case-based system in Nigeria, which applies to Bayelsa State. A secondary data of measles case-based surveillance data from the state IDSR001C with age, sex, LGA, vaccine dose, date of onset, month of reporting and IgM results were collected on excel spreadsheet from January to December, 2022. Measles vaccination post campaign coverage report from the State WHO office was also used. Cases were defined according to WHO standard case definition as follows:
A suspected case: is the occurrence of fever and a maculopapular rash with any one of cough, coryza, or conjunctivitis or any illness in a person that a clinician suspects to be measles.
A confirmed measles case: is classified as either laboratory-confirmed or epidemiologically linked.
Laboratory confirmed case: when measles-specific IgM antibody is detected in serum by enzyme-linked immunosorbent assay (ELISA) in the absence of measles vaccination within 30 days before specimen collection . Epidemiologically linkage is usually unreliable, therefore for this study only cases with IgM result were used.
Outbreak confirmation: Routinely measles outbreak is confirmed by collecting blood samples from 5 suspected measles cases when the number of suspected cases exceeds the measles outbreak threshold (usually more than 5 cases in a district in a month). If as few as 2 out of 5 suspected measles cases are laboratory confirmed, the outbreak is confirmed .
The following activities were conducted leading to the campaign:
Update of training manual on measles vaccine
Development of measles micro plan to ensure a cohesive and successful process
Training of healthcare workers using updated training manual and micro plan template
Conducting advocacy, communication and social mobilization (ACSM) activities. Advocacy to key stakeholders across all levels including the traditional, community and religious leaders within the community through the Ward Focal Person informing them of the start of the process and collaboration for them to be part of the microplanning process. Also, advocacy visit to line ministries i.e. Ministry of Health; Women, Children Affairs, Empowerment and Social Development; Information, Orientation and Strategy; Education; Local Government Service Commission, followed by series of community engagement and communication strategies were carried-out with community heads within all the affected settlements. Clear messaging to affected communities was propagated on the reason for the response. (this is essential for their buy-in, to ensure everyone and place within their catchment area are fit into the micro plan and properly planned for).
Flag off campaign activities.
Data was retrieved and analyzed in Microsoft Excel 2016 and SPSS version 20. Relevant variables were cleaned, sorted and extracted from MS-Excel database. The measles cases were described in person, place and time and basic statistical analysis was done with counts, proportions and averages. Positivity rate was also calculated from this data by dividing the total confirmed cases by the totals cases tested, multiplied by 100. Only measles cases for which specimen were collected and tested from January to December 2022 were used for this analysis. The association between number of measles vaccine doses and IgM result was determined using chi-square, P value was observed with 5% significance level.
Ethical approval was obtained from the State Ministry of Health Ethical committee to conduct this survey and disseminate relevant findings.
The epidemiological characteristics of suspected and confirmed cases are summarized in Table 2 below.
The modal week of confirmed cases was week 11(March) with 16 positive cases (Fig.2). During the study period, there were a total of 14 measles outbreaks in six LGAs, one in Sagbama, two each in Yenagoa and Brass LGAs and three each in southern Ijaw, Ogbia and Ekeremor LGA. Regarding monthly trend of confirmed cases, there were confirmed cases every month but March and June had the highest proportion of cases (19.9% and 18.5%, respectively). (Fig. 3). A total of 450 suspected measles cases were reported from January to December, 2022, out of which 151 were laboratory confirmed (IgM+) for measles giving a case positivity rate (PR) of 34%, one death was reported, giving a case fatality rate (CFR) of 0.7%. Of the 151 laboratory-confirmed cases, 51% were males, and 45.7% were under five years of age. Children under-five years had a median age of 2. The frequency of distribution of the 151 confirmed cases according to LGAs was; Yenagoa-56 (37.1%); Southern Ijaw-32 (21.20%); Ekeremor-24 (15.9%); Ogbia-19 (12.6%); Sagbama-8 (5.2%); Brass-10 (6.6%); and Kolokuma-Opokuma-2 (1.3%) (Fig.4).
The study shows that only 5.3% of the confirm cases were zero dose, one dose made up 28.5% why two and three dose was 24.5% and 9.9% respectively. No significant relationship between the number of vaccine doses and the Igm result, the chi-square test yielded a chi-square statistic of 3.671 with 4 degree of freedom (P value = 0.452 at 5% significance level) (see table 2 above).
Measles Vaccination Campaign
The vaccination coverage according to LGAs was as follows; Ekeremor (101%), Nembe (97%), Brass (92%), Ogbia (90%), Sagbama (87%), Southern-Ijaw (91%), Yenagoa (74%) and Kolokuma-Opokuma (31%) (Fig. 5). The total number of children targeted for the November 2021 measles mass vaccination campaign was 358,156, while the total number of children who received the measles vaccine in Bayelsa State was 308,718. The post vaccine coverage was 86% (Fig. 6).
Despite significant progress over the previous decade, measles remains a top cause of death among young children in low-income countries [45, 46]. Supplemental immunisation activities (SIAs), which are periodic national or regional campaigns aiming at administering vaccine to everyone in a particular age range, are the principal measles control efforts in addition to normal vaccination [47-49]. Thus, from January to December 2022, this study examines the epidemiology of measles in Bayelsa State, south-south Nigeria. In the confirmed cases, men outnumber women 51% to 49%. There is no known sex predisposition, as unprotected males and females remain equally susceptible to measles virus infection [3, 21, 33]. Children under the age of five were the most impacted, with a 45.7% positive rate, which is consistent with previous research [50-53]. The results show a 34% test positivity rate and a 0.7% case fatality rate. The positive rate in this study is rather high in comparison to the 86% vaccination coverage obtained in the study; however, the case fatality rate is slightly higher than the 0.6% benchmark in Nigeria [33, 54-56]. According to the study, Yenagoa LGA, the state capital, had 74% vaccination coverage and the greatest number of confirmed cases. This has been attributed to inadequate immunisation coverage in metropolitan slums as well as the sensitivity of surveillance in the state capital [3, 18, 20, 57, 58]. Despite 86% immunisation coverage, measles transmission occurred throughout the year, with peaks in February, March, and June. In Nigeria, measles transmission occurs throughout the dry season (February, March, and April) [4, 33], which is in accordance with earlier studies conducted in the state [33, 54]. likewise, Ekeremor, Southern Ijaw, and Ogbia each reported three outbreaks with 15.9%, 21.2%, and 12.6% of confirmed cases, respectively, with vaccine coverage of 101%, 91%, and 90%. A significant proportion of confirmed cases among vaccinated people could be ascribed to cold chain or vaccination administration difficulties. Similarly, measles outbreaks have been reported in places where a substantial proportion of the population has received a single dose of the vaccine [33, 47, 49, 51]. Kolokuma-Opokuma reported only one confirmed case of measles, while having the lowest vaccination coverage (31%). This could be due to low monitoring sensitivity and erroneous population estimations [3, 46, 51]. Finally, the result showed that there is no significant relationship between the number of vaccine doses and the IgM results. Studies by Aworabhi et al.,  in Bayelsa state showed the same significance relationship but a different distribution of cases, zero dose had 51.7%, one dose had 42.8% and two dose 5.5%. This work is not without limitations; the reported data from the Bayelsa state surveillance system had 31.8% confirm cases with unknown immunization status which is about 29% of our study population. The vaccination status of confirm cases relies on recall in absence of vaccination card, and can lead to over or under estimation of vaccine doses. The targeted population may not reflect the accurate number of eligible children, reason that the last census was conducted in 2006, hence coverage data may not reflect actual proportion vaccinated. Finally, surveillance data may also have underestimated the burden of the disease due to under-reporting.
Ultimately, the core solution to measles control lies in routine vaccination with at least two doses of measles-containing vaccine (MCV) but, in much of the world, SIAs are relied upon to achieve adequate coverage. However, even countries thought to have highly successful control sometimes experience large outbreaks because of unnoticed build-up of susceptible individuals, as recently occurred in countries such as Zambia, Malawi, and Burkina Faso [1, 2, 59]. The 2009 WHO guidelines for outbreak response in mortality reduction settings and the WHO Global Measles and Rubella Strategic Plan for 2012–2014 extended the classic “static” control strategies (routine immunization and SIAs occurring at intervals determined by the level of routine coverage) to include the possibility of reactive responses [11, 12]. Outbreak response vaccination (ORV) was recommended for outbreaks occurring in measles mortality reduction areas [2, 4, 60], based on evidence that epidemics build sufficiently slowly that large numbers of cases can be averted given a sufficiently prompt reaction [7, 23, 25, 49]. ORV has also been recommended in elimination settings, where a single case should lead to appropriate outbreak investigation and response, including vaccination of susceptible people in as wide an area as possible [1, 50, 57]. Identifying the most effective strategies for outbreak response immunization activities has been posed as one of the key issues in a recent review of research priorities for measles eradication. However, although there has been a range of quantitative analyses on the impact of varying characteristics of static immunization strategies (e.g., the interval between SIAs) [3, 10, 18], investigations of the outcomes of reactive vaccination coverage are rare. Ferrari and colleagues showed that ORV might be key to reducing the case burden in the context of irregular, violent measles dynamics in Niger. This inferred impact of reactive vaccination echoes theoretical analyses showing that average outbreak size grows exponentially with the delay from the start of an outbreak to the implementation of an intervention [18, 30, 52, 53, 59, 61]. Beyond these few analyses, little is known.
In conclusion, Bayelsa state reported 14 measles outbreaks despite immunization campaign with vaccine coverage of 86%. The result from the studies showed that the number of vaccine doses had no significant impact on the measles incidence. As a result, it is advised that errors in cold chain storage and vaccine administration be prevented through effective training and monitoring of immunisation teams, particularly during SIAs. Authorities in charge of primary health care should prioritise communities with zero doses and provide the necessary security for health professionals to visit urban slums during vaccination. To avert disease outbreaks, the LGA monitoring team should boost case discovery to increase early case detection and reporting. Only with a solid disease monitoring system in place can the success of prevention and control programmes in lowering morbidity and death from vaccine-preventable diseases be quantified. In 2006, measles case-based monitoring began in Nigeria, utilising the resources and infrastructure already in place for Acute Flaccid Paralysis surveillance. As a result, the basis for ensuring and maintaining high population immunity against measles is a strong, well-functioning national immunisation strategy that achieves high coverage with two doses of MCV. Supplemental actions are sometimes required while laying this foundation to close immunity gaps by reaching children who have received no or only one dose of MCV. A third key technique for halting measles virus transmission and avoiding future spread is rapid epidemic detection and response.
The authors declare that they have no competing interests
No funding was received for this study.
Abaya S T: He was responsible for the conception of the problem, design, collection, analysis and interpretation of data and drafting of final article. Ogoina D: Participated in the design, conception and critical review of final draft. Abaye B B: Had oversight of all stages of the research and critically reviewed the final draft of the article. Adedamola T: He was responsible for the design, analysis and interpretation of data and drafting the final article.
We acknowledge the effort of Dr. Morufu Olalekan Raimi, the Technical Adviser to the Executive Secretary, Bayelsa State Primary Health Care Board for his frank collaboration in the framework of this research and the Epidemiology Department of the Bayelsa State Ministry of Health and the Bayelsa State WHO office for working together to get all the data used for this study.
The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request
WHO: World Health Organization
IDSR: Integrated Disease Surveillance and Response
SIA: Supplementary immunization activity
CFR: Case fatality rate
MCV: Measles-Containing Vaccine
LGAs: Local Government Area
DSNO: Disease Surveillance and Notification Officer
NCDC: Nigerian Centre for Disease Control and Prevention
ACSM: Advocacy, communication and social mobilization
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