|Year : 2020 | Volume
| Issue : 3 | Page : 156-162
Rubella transmissibility and reproduction number (Ro): A critical appraisal of the prospects for its control in Nigeria
Kabir Adekunle Durowade1, Omotosho Ibrahim Musa2, Gordon Kayode Osagbemi2
1 Department of Community Medicine, Afe Babalola University, Ado-Ekiti; Department of Community Medicine, Federal Teaching Hospital, Ido-Ekiti, Nigeria
2 Department of Epidemiology and Community Health, University of Ilorin and University of Ilorin Teaching Hospital, Ilorin, Nigeria
|Date of Submission||16-Apr-2020|
|Date of Decision||05-May-2020|
|Date of Acceptance||10-May-2020|
|Date of Web Publication||17-Jul-2020|
Dr. Kabir Adekunle Durowade
Department of Community Medicine, Afe Babalola University, Ado-Ekiti
Source of Support: None, Conflict of Interest: None
Rubella is a highly contagious disease of public health importance that is endemic in Nigeria. Rubella with its devastating sequel, congenital rubella syndrome, is a neglected disease with no surveillance system in place and no national incidence figure in Nigeria. This article, therefore, seeks to do reviews of rubella transmissibility, its reproduction number and the prospects for its control in Nigeria. This is a review of literatures with triangulation of findings along the objectives and the use of available secondary data to analyse the prospects of rubella control in Nigeria. Data were analysed and presented with appropriate tables and charts. A number of factors can fuel rubella transmission causing increase in reproduction number, Ro.The high birth rate, poor rubella surveillance and non-inclusion of rubella vaccines in the routine vaccination schedule among others are some of the factors working against a good outlook for rubella control in Nigeria. The Nigerian government should control the growing population, ensure a robust surveillance for rubella and incorporate rubella-containing vaccine in the immunisation schedule for infants with regular vaccination campaigns for older children and adults.
Keywords: Nigeria, reproduction number, rubella-containing vaccine, transmissibility
|How to cite this article:|
Durowade KA, Musa OI, Osagbemi GK. Rubella transmissibility and reproduction number (Ro): A critical appraisal of the prospects for its control in Nigeria. Niger Postgrad Med J 2020;27:156-62
|How to cite this URL:|
Durowade KA, Musa OI, Osagbemi GK. Rubella transmissibility and reproduction number (Ro): A critical appraisal of the prospects for its control in Nigeria. Niger Postgrad Med J [serial online] 2020 [cited 2021 Jun 13];27:156-62. Available from: https://www.npmj.org/text.asp?2020/27/3/156/289921
| Introduction|| |
Rubella, otherwise called German measles, is a vaccine-preventable viral disease of public health significance caused by the rubella virus. It is a mild febrile illness affecting children and adults, and these two symptoms of fever and maculopapular rash are common presentations of the disease. The rubella rash, occurring in at most 80% of infected persons, is at times wrongly diagnosed as measles or scarlet fever. Other symptoms include posterior auricular and suboccipital lymphadenopathy, headache and myalgia among others. Rubella infection in the first 3 months of pregnancy affects the foetus leading to spontaneous abortion, foetal death or a baby born with disabling conditions called congenital rubella syndrome (CRS) in up to 90% of cases.,, The CRS affects virtually all organs causing disease conditions which include heart disease, blindness and deafness., Other congenital defects are ocular (cataracts, retinitis, microphthalmia and glaucoma), hearing impairment, cardiac (pulmonic stenosis and persistent ductus arteriosus), microcephaly, delayed milestones, impaired intellectual ability and impaired hepatic and splenic function including intrauterine foetal death.,
Serological studies done across Nigeria have shown that rubella is endemic in Nigeria. A study done in Kebbi State, Northwest Nigeria, between 2014 and 2015, among 413 symptomatic children revealed that 3.5% tested positive for rubella IgM in 2014 while 2.6% were positive in 2015. Seroprevalence values of 66.6%, 77% and 93.5% were obtained in Imo, Lagos and Oyo, respectively, among women in the childbearing age. In Ilorin, Nigeria, Agbede et al. obtained a seroprevalence of 16.3% among 92 pregnant women and 87% (IgG seropositivity) and 1.5% (IgM seropositivity) among women aged 15–49 years. Another study in Ilorin, Nigeria, found almost a tenth (8.1%) to be seropositive for rubella IgM antibody, and all (100%) the subjects with rubella IgM antibodies had rubella IgG antibodies. In Osogbo, Southwest Nigeria, 175 (87.5%) were positive and more than three quarters, 85%, had a positive result among those aged 30 to 34 years (P = 0.716). Despite the devastating sequel of this condition and the high serological prevalence in Nigeria, rubella screening and vaccination of women and children against the disease is neither part of antenatal schedule nor among the diseases targeted for vaccination in the routine immunisation. As rubella is not part of the disease on the routine immunisation schedule and given the burden of the disease, surveillance and control of the disease is of utmost importance. This review examines the reproduction number, transmission and prospects of rubella control in Nigeria.
| Methodology|| |
Internet search was achieved using Google Search, PubMed, MEDLINE and AJOL. A total of 20 review articles (RA), 17 original articles (OA), 17 internet articles (IA) and 6 textbooks (TXT) were initially retrieved, reviewed and findings triangulated. However, 15 RA, 12 OA, 13 IA and 3 TXT were used to achieve the final write-up. Excluded materials are 5 RA, 5 OA, 4 IA and 3 TXT. Predominantly, the time interval of source documents ranges from the years 2000 to 2019. The diagrammatic representation is shown in [Figure 1].
| Reproduction Number and Transmissibility Potential of Rubella|| |
A factor that determines the person–person transmission of infectious diseases like rubella is the sum total of infections arising secondarily following contact with a primary case. Therefore, reproduction number, Ro, an index of transmissibility of an infection, is the average number of secondary infections caused by the primary case of the disease in a susceptible population. Unlike measles, Ro of rubella is generally lower (about 4–7) except in high-density settings where the values could be as high as 11.8 as reported in a densely populated region of Addis Ababa by Cutts et al. If Ro is <1, the average case of the disease gives rise to <1 case and transmission cycle ceases. Ro= τp · c · d where τp is the transmissibility potential (chance of infection occurring sequel to interface between susceptible and infected individuals), c is the average rate of contact between susceptible and infected individuals and d is the duration of infectivity.,
Practically, the reproduction number, which is dimensionless and not a rate, can be calculated using several approaches. A direct relationship exists between reproduction number, Ro, and transmissibility potential, τp, of an infectious disease. Mathematically expressed as Roα τp; Ro=Kτp where K is a mathematical constant. However, for immunizable infections like rubella, the proportion of susceptible population is estimated using average age (A) at which infection occurs to divide the average life expectancy, (L) in years, which is Ro= L/A. For populations characterised by exponential age structures like Nigeria, more robust estimate of Ro can be obtained using the equation: Ro= 1 + L/A. Therefore, while the reproduction number, Ro, has an inverse relationship with the average age at infection, A has a demonstrable direct linear relationship with the transmissibility potential, τp, of an infection. The lower age of infection for rubella seen in Nigeria will, therefore, translate to a higher reproduction number, Ro, and increase transmissibility potential, τp. Consequently, control programmes/strategies for rubella should aim to keep the Ro below 1.
| Prospects of Rubella Control in Nigeria|| |
To examine the prospect of rubella control and to keep the rubella reproduction number below 1, the following areas of impact on the Ro need to be examined. These are births, migration and surveillance for rubella. Others are rubella vaccination, diagnosis of rubella and budgetary allocation to health.
| Births|| |
In general, births and immigration increase population susceptibility and also increase Ro. Nigeria has a birth rate of about 36.9/1000 population as at 2017 [Figure 2] which is relatively high when compared with Ethiopia and in the USA. Similarly, as shown in [Figure 3], Nigeria's fertility rate is 5.59 births/woman; however, in Ethiopia, it is 4.32 births/woman. Projection shows that, by the year 2050, Nigeria will rank third world's most populous country and one of the six with more than 300 million people. In the absence of rubella vaccination, higher birth rates/population in Nigeria will lower average age of infection. With higher birth rate, the transmission intensity may be higher (increasing τp and Ro), thereby lowering the average age of infection making it cumbersome breaking transmission of rubella. Evidences suggest that rubella has a huge critical population mass above which random extinction does not occur, and in the presence of geographically heterogeneous vaccination uptake, build-up of susceptible individuals occurs., Consequently, with Nigeria's large population size, in the absence of rubella vaccination, control effort may be jeopardised.
|Figure 2: Crude birth rates and total population in selected countries (2000–2017)|
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| Migration|| |
Globally, human migration and mobility is a topical feature in the debate on disease risks linked with increasing population movement across international borders. International mobility is key to the transmission and globalisation of diseases fuelling the spread and increasing Ro. Anxiety about imported diseases and the resultant local consequences has over time got amplified by external desire for socio-economic activities. Rubella, just like many other infectious diseases, can be imported through international borders to other countries with the possibility of not being detected. Cases of imported rubella, especially foreign visitors, may spread the virus (increasing Ro) without seeking healthcare, and similarly, adult immigrants from countries with no vaccination programmes are equally susceptible to rubella. Therefore, as international and cross-border migration increases, the chances of having increasing incidence of imported rubella get on the rise with increasing transmission. In Nigeria, just like many other countries in Africa, rubella vaccinations are not updated or verified in immigrants on arrival, and there is no system in place to vaccinate for rubella at the entry port. This systemic gap poses a threat to rubella control in Nigeria, especially when there is no rubella vaccination programme in the country.
| Surveillance for Rubella|| |
Disease surveillance is very key in the control of disease and disease outbreak. However, just like in most other countries within the African region of the World Health Organization (WHO), rubella is not notifiable in Nigeria. Despite the burden of the sequel associated with rubella infection, Nigeria does not have a separate surveillance system for rubella and CRS but rather integrated with measles case-based surveillance. A separate surveillance system for rubella may be more cost-effective in terms of improving case detection, decrease transmission (decrease τp and Ro) and reducing the pressure on the measles surveillance system. It will also entrench prompt release of results from the laboratory, early collation of data for surveillance activities and prompt institution of intervention, where necessary, to reduce transmissibility. Just like Nigeria, many African countries also have an integrated national measles and rubella surveillance to establish the disease burden. Therefore, the need to strengthen surveillance of rubella as a precursor to its control cannot be overemphasised. This is because surveillance of rubella and CRS is important towards evaluating the burden before and after the introduction of rubella-containing vaccine (RCV). It also helps in detecting rubella-infected gravid women requiring follow-up to evaluate pregnancy outcomes, to diagnose and to treat infants with CRS.
| Rubella Vaccination|| |
As shown in [Table 1], rubella vaccine is a live-attenuated vaccine; it can come as monovalent, bivalent (measles–rubella [MR] combination) and as a trivalent combination (mumps, measles and rubella [MMR]). It is a lyophilised vaccine with a diluent for reconstitution. According to the WHO, rubella vaccine was in use in 162 countries as at the end of 2017 with a global coverage estimate of 52%. As stated by Chimhuya et al., rubella vaccination represents the most effective intervention for its control (decreasing Ro), prevents devastating sequel, reduces huge financial cost of care for children with CRS and averts death from complications. The WHO advocates that countries introduce RCVs to reduce viral circulation in population, scale up herd immunity (decreasing Ro) and indeed reduce the incidence of CRS. As a preliminary step towards introducing RCVs, the WHO approves that countries use vaccination campaigns strategy to introduce the vaccine before replacing monovalent measles vaccine with bivalent MR vaccine in their respective vaccination schedules. In addition, to stop the displacement of rubella susceptibility and spread among older populations and pregnant women with attendant potential increase in CRS burden, the WHO further recommends that countries achieve a 80% coverage in routine measles vaccination and or supplemental immunisation activities before MR introduction.
In the 14-year period between 1996 and 2009, there were only two counties in Africa out of the 47 member states that introduced RCVs. As shown in [Figure 4] and [Figure 5], other regions of the WHO had an appreciable rise in number of countries that adopted the use of RCV in the period considered. By the year 2009, all countries in the America and European regions have adopted the RCV in their National Immunization Schedule. However, this cannot be said of the countries in African region including Nigeria as only the duo of Mauritius and Seychelles has introduced MR vaccine and first in the continent to vaccinate against rubella. By June 2017, 15 other countries carried out mass vaccination campaigns using MR vaccine before its introduction in routine vaccination programmes. These countries are Botswana, Burkina Faso, Cameroon, Cape Verde, Gambia and Ghana. Others are Kenya, Namibia, Rwanda, São Tomé and Principe, Senegal, Swaziland, Tanzania, Zambia and Zimbabwe.
|Figure 4: Number of countries in the six World Health Organization regions using rubella-containing vaccine in their national schedule|
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|Figure 5: Percentage of countries in the six World Health Organization regions using rubella-containing vaccine in their national schedule|
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In a study by Luce et al., analysing the case-based surveillance data of the five countries in Africa that introduced the MR vaccine in 2013–2014, a reduction in number of cases (decreasing τp and Ro) of rubella was recorded; as Ro and τp increase, higher immunisation coverage is needed to achieve herd immunity and elimination of an infectious disease. The reproduction number, Ro, measures the transmissibility (τp) of an infection, and it is the composite secondary infections arising from an infected person in a susceptible/unvaccinated population with no herd immunity. If Ro is <1, an average case will result in <1 case and transmission cycle stops. As a result, for Nigeria to have a good prospect to control rubella, there is the need to introduce the RCV in the national schedule. Despite its relatively low price, inclusion of rubella vaccine to the schedule might be financially unbearable for countries like Nigeria. This is because the healthcare budgets are below the recommended 15% and are already stretched. It will also be financially demanding to achieve a high level of vaccination coverage (>80%). However, this becomes very necessary to achieve a reduction in the incidence of CRS which would occur if poor coverage of vaccines minimised viral circulation in the population sufficiently enough to skew rubella susceptibility from children to young non-immune mothers. The inclusion of rubella vaccination in the national schedule is both cost-beneficial and cost-effective. Studies across both high- and middle-income countries have shown that cost of care for CRS is much higher than the cost of rubella vaccination to prevent it., A cost–benefit analysis of rubella vaccination in Japan evaluated the programme for a couple planning pregnancy. Economic evaluation revealed that more than 5000 cases of rubella among men and 1727 in women were prevented in the base case model for couples. Furthermore, 34 cases of CRS were averted by the programme. In the Caribbean country of Barbados and in Guyana, South America, the lifelong cost of care for a CRS case was estimated to be 50,000 and 64,000 Dollars, respectively. Conversely, the rubella vaccine is financially accessible with the marginal costs of introducing RCV in both the bivalent (MR) and trivalent (MMR) vaccines using a 10-dose vial being less than a Dollar ($0.31) and <2 Dollars ($0.70–$1.37) at most for a dose, respectively. These studies underscore the importance of introducing RCV to control rubella to reduce Ro
| Diagnosis of Rubella in Nigeria|| |
Just like in many African countries, the diagnosis and reporting of rubella or CRS needs to be improved. Rubella case-based surveillance data and laboratory results are captured through a computerised data management system at the national level, but the laboratory diagnosis of these conditions has been bedeviled with myriad of problems, thereby affecting data for surveillance activities in Nigeria. Nigeria, being a party to the 2005 International Health Regulations, commits herself to provide needed resources to identify (through laboratory diagnosis), guide against and adequately rise up to confront public health emergencies. This underscores the importance of timely and accurate diagnosis of these conditions through functional laboratories, but unfortunately, these laboratories have been performing suboptimally due to paucity of funds and poor budgetary provision and inadequate workforce. Timely and accurate diagnosis will enhance rubella control through prompt institution of intervention to prevent transmission, thereby decreasing τp and Ro.
| Budgetary Allocation to Health|| |
In the year 2001, the African Union countries met in Abuja and made a declaration to allocate not <15% of total annual budget to the health sector. In another meeting (Abuja + 12 meeting) in July 2013, Nigeria again hosted 50 African Heads of State to review the progress made on the commitment at the Abuja Declaration. However, 10 years after the declaration, only Tanzania achieved the benchmark of at least 15%., As at now, more than 15 years after the declaration, only a few African countries reached this target and Nigeria is not one of these countries., The African countries that have achieved the minimum of 15% budgetary allocation included Tanzania, South Africa Rwanda, Zambia, Botswana, Liberia, Malawi and Togo. From the 10-year trend graph [Figure 6], as seen for the year 2017, Nigeria's health budget was 4.17% of its total budget. The fund allocated for immunisation was 22.5% of the total capital health budget, most of which was not actually released. In 2018, there was a funding gap of 16 billion Naira on immunisation in Nigeria, as shown in [Figure 7]. As shown in [Figure 8], Nigeria spends only 29% and 24% of the required sum on routine vaccination in 2015 and 2016, respectively, and budgetary allocation to health in Nigeria has consistently faltered below the 2001 Abuja Declaration benchmark of 15%. With Nigeria's growing population, coupled with the dwindling financial support from donor agencies, domestic funding for immunisation needs to be scaled up.,, The African countries, which have incorporated rubella vaccination in their immunisation schedule, have been able to attain the 15% budgetary provision for health, hence buttressing the need to scale up health budgetary provision as a precursor for improved immunisation funding. The WHO recommended that countries spend a minimum of 5% of gross domestic product (GDP) on health, and some African countries have been able to achieve this target. However, in the 15-year interval (between 2000 and 2015) [Figure 9], Nigeria moved from 2.6% to 3.6%. Total health spending (as percentage of GDP) in Nigeria was 3.67 in the year 2014. Its peak value over several years was 4.47 in 2007, while its lowest value was 2.43 in 2002, and most of these expenditures are more of private spending. Consequently, for Nigeria to be on the track towards the control of rubella, deliberate efforts by the government are necessary to improve health expenditure directed at appropriate interventions to address these gaps in control effort.
|Figure 8: Percentage of government expenditure on routine vaccination|
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|Figure 9: Percentage of country gross domestic product spent on health in some African countries|
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| Conclusion/recommendations|| |
Reproduction number, Ro, of rubella fuels its transmission potential, and this is aided by the population density and a number of other factors, which impacts on the prospects of its control. Nigeria has a high birth rate and no rubella vaccination policy for each birth cohort. Added to this are the poor migration policy together with lack of rubella surveillance and poor budgetary allocation to health (as evidenced by immunisation funding gap). The outlook of these factors, as presented, will aid the continuous endemic transmission (with increasing τp) of rubella causing increasing Ro. Therefore, with these indices, Nigeria has poor prospect towards rubella control as these parameters are still faltering below the expectation. All efforts and machineries should be put in motion by the Nigerian government to incorporate RCV in the routine immunisation schedule. Rubella surveillance should be enhanced and made more prominent by the Federal Ministry of Health as against being subsumed under the measles surveillance as it is currently being practiced. The diagnosis of the disease needs to be enhanced by the government through improved logistics in terms of human, financial and material resources. Rubella vaccination can also be made compulsory by the government for all international travellers coming into Nigeria. Furthermore, the budgetary allocation to health should be improved upon in Nigeria by the government, at least to the minimum 15% as agreed in the Abuja 2001 Declaration. In particular, the persistent immunisation funding gap should be adequately bridged by the government in Nigeria and funding scaled up to accommodate the debut of the RCV into our national schedule.
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Conflicts of interest
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