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 Table of Contents  
ORIGINAL ARTICLE
Year : 2018  |  Volume : 25  |  Issue : 3  |  Page : 137-142

Comparative tetanus antibody response of Nigerian children to diphtheria-pertussis-tetanus and pentavalent vaccines


1 Department of Paediatrics, University of Calabar Teaching Hospital, Calabar, Nigeria
2 Department of Paediatrics, University of Calabar, Calabar, Nigeria
3 Department of Chemical Pathology, University of Calabar, Calabar, Nigeria
4 Department of Internal Medicine, University of Uyo, Uyo, Nigeria

Date of Web Publication26-Sep-2018

Correspondence Address:
Emmanuel Eyo Ekanem
Department of Paediatrics, University of Calabar, Calabar
Nigeria
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/npmj.npmj_41_18

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  Abstract 

Background: In Nigeria and many parts of the world, the pentavalent vaccine is replacing the diphtheria-pertussis-tetanus (DPT) vaccine in tetanus prevention. Aims and Objectives: The aim of this study was to compare the anti-tetanus immunoglobulin G (IgG) response of children who received DPT with those who received the pentavalent vaccine. Subjects and Methods: A cross-sectional survey of anti-tetanus IgG levels in children aged 6 months to 5 years who received DPT and in children who received the pentavalent vaccine. IgG antibody levels were determined using enzyme-linked immunosorbent assay. The protective level was set at ≥0.1 IU/ml. Results: One hundred and twenty-two out of 130 children (93.9%) who had received DPT had protective levels of anti-tetanus IgG compared to 278 out of 288 children (96.5%) who had received the pentavalent vaccine. The difference was not statistically significant (P = 0.21). The median IgG antibody level in those who received DPT was 1.1 IU/ml (interquartile range (IQR) 0.4–1.8) compared with 0.6 IU/ml (IQR 0.4–1.4) in those who received pentavalent vaccine (P = 0.006), with age being the only predictor of variability in the multivariate analysis. Conclusion/Recommendation: DPT and pentavalent vaccines are equally effective in inducing protective levels of anti-tetanus IgG in children. Vaccination with the pentavalent vaccine, which is the current policy in Nigeria and many other parts of the world, should continue.

Keywords: Anti-tetanus immunoglobulin G, diphtheria-pertussis-tetanus, pentavalent vaccine


How to cite this article:
Uket HO, Ekanem EE, Okpara HC, Ekrikpo UE. Comparative tetanus antibody response of Nigerian children to diphtheria-pertussis-tetanus and pentavalent vaccines. Niger Postgrad Med J 2018;25:137-42

How to cite this URL:
Uket HO, Ekanem EE, Okpara HC, Ekrikpo UE. Comparative tetanus antibody response of Nigerian children to diphtheria-pertussis-tetanus and pentavalent vaccines. Niger Postgrad Med J [serial online] 2018 [cited 2018 Oct 19];25:137-42. Available from: http://www.npmj.org/text.asp?2018/25/3/137/242203


  Introduction Top


Tetanus is a significant public health problem that occurs worldwide.[1] It is a major cause of morbidity and mortality in the under-fives.[2] Around 1 million deaths are attributed to tetanus each year.[3] About 80% of these deaths occur in Africa and South East Asia, and the disease remains endemic in 90 countries around the world including Nigeria.[3] The World Health Organisation (WHO) identified tetanus as the highest mortality contributor to children after measles among vaccine-preventable diseases.[4] In 2013, there were 556 cases of tetanus in Nigeria but none in South Africa.[5] Post-neonatal tetanus is a major problem in Nigeria.[6],[7],[8],[9],[10] Tetanus is completely preventable.[11] Improved hygiene, focussed health education, as well as the use of tetanus toxoid, are veritable tools for the prevention of tetanus.

Prevention of tetanus is basically by vaccination and immunisation.[12],[13] Vaccination is the process of administering a vaccine which is either a killed or weakened organism or modified toxins to achieve protection against disease.[14] Immunisation is the protection gotten either via vaccination or previous exposure to the disease.[14] It is important to note that one can be vaccinated but not immunised. This implies that the vaccine is received, but protection is not achieved. Three doses of tetanus toxoid are recommended to all infants as the routine immunisation programme by the WHO.[11] In Nigeria, the primary vaccination in the National Programme on Immunisation is given at 6 weeks, 10 weeks and 14 weeks.[15] Until 2012, tetanus toxoid was given as diphtheria-pertussis-tetanus (DPT) combination. However, in 2012, the Pentavalent vaccine, which is a combination of DPT plus Hepatitis B virus (HBV) and haemophilus influenza (Hib) vaccination was launched. However, this was not available in Calabar, Cross River State until July 2013.

Serological surveys have been strongly recommended to appraise the impact of vaccination to improve immunisation policies and reduce the disease burden.[8] The gold standard for the determination of their anti-tetanus antibody levels with a protective cut-off value of 0.1 IU/ml is the enzyme linked immunosorbent assay (ELISA).

The aim of this study was to compare the anti-tetanus antibody levels in Nigerian children aged 6 months–60 months who had received plain DPT with those who had received the pentavalent vaccine. In addition, the study aimed to find possible predictors of variability if any, including the age, gender and social class. This was a cross-sectional study that may help assess the appropriateness and effectiveness of the efforts targeted at preventing post-neonatal tetanus in the country.


  Subjects and Methods Top


Study location

The study was carried out at the University of Calabar Teaching Hospital (UCTH), Calabar, Cross River State of Nigeria from June 2015 to January 2016. Cross River State is situated in the south-south geopolitical zone of Nigeria. Calabar, the state capital, has two Local Government Areas (Calabar Municipality and Calabar South). UCTH is the sole tertiary health facility in the Calabar Municipality Local Government Area.

Sample size determination

In a prospective study conducted by Orimadegun et al.[16] among 304 hospitalised children aged 1–9 years in Ibadan, Oyo State, the prevalence of protective immunity against tetanus using ELISA after three doses of DPT vaccine was 44.7%.[16] This prevalence rate was used in this study to derive the sample size of a minimum of 380 children using the formula n = z2.p.(1 − p)/(e. p) 2.

Patient recruitment and selection criteria

This study was conducted in the Department of Paediatrics, UCTH. The Department has four service sections-the Children Outpatient Clinic (CHOP), the Newborn Unit, the Children Emergency Room (CHER) and the paediatric ward. Well-nourished children (those with weight-for-height >−1, z-score > 90%)[17] between the ages of 6 months and 5 years who were attended to in CHOP, CHER, and the ward for acute illnesses and had met the inclusion criteria were recruited. Immunisation cards were inspected to identify those who had completed three doses of DPT/pentavalent vaccine for final eligibility. Socio-demographic characteristics (gender, age, ethnicity, parent's educational level and occupation) were collected. Socio-economic classes of participants were assessed using the method employed by Oyedeji.[18] The last date of DPT/pentavalent vaccines was noted and blood samples were then taken for determination of immunoglobulin G (IgG) levels. The children were separated into two groups. The first group was those who received plain DPT vaccine while those who received the pentavalent vaccine were in the second group.

Ethical issues

Ethical Approval – Ethical clearance for the conduct of this study was obtained from the Ethics Committee of the UCTH with letter reference number UCTH/HREC/33/258 dated 11th August 2014.

Informed consent

Parents or guardians of children in the different paediatric wards were given a copy of the statement of the study which they read to gain a good understanding of the nature of the study. They had the unconditional option of giving or declining consent for participation of their child or ward. The screening form for eligibility was given to them to fill to select those eligible for the study. The nonnegative consequences of withdrawing a child or ward from the study were elaborately explained to parents or guardians.

General clinical assessment of subjects

Following informed consent obtained from parents or guardians, the child's bio-data and information on present illness, the past medical and immunization history were obtained from the patients by use of a semi-structured questionnaire. Immunisation status was confirmed for each child by visualising the card via physical presentation of the card at the clinic, social media presentation, or home acquisition of the card. Those whose cards were unavailable were excluded from the study.

Patient preparation, specimen collection and preservation

The specimen collection procedure was explained to the parents or guardians before venepuncture. A volume of 3 ml of venous blood was obtained from each eligible child under aseptic procedure into a clean plain nonanticoagulated sample bottle and allowed to clot. The samples were transported in a cooler of ice to the paediatric side laboratory within 1–2 h of collection. The clotted sample was centrifuged at 5000 rpm for 5 min. The supernatant serum was separated and transferred to storage tubes and stored at −20°C for a maximum of a week before batch analysis. Labelling was done with coded numbers to avoid mistakes. The samples were analysed using an ELISA test kit (Tetanus toxin IgG, DRG International, Inc., Marburg, Germany).[19] The kit was stored and preserved at a refrigerator temperature of 2°C to 8°C until completion of the study.

Interpretation of results

The manufacturer kit-dependent protective antibody level using this assay was ≥0.1 IU/ml [Table 1].[19]
Table 1: Interpretation of the anti-tetanus toxin antibody concentration in serum

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Analytical quality control

The concentrations of anti-tetanus toxoid antibody in the negative and positive control sera were read from the calibration curve. Calibrators and controls were included in each run. The obtained values were compared with the range given on the national quality control (QC) certificate. Curve shape was similar to the calibration curve shown in the QC certificate. Acceptable run was determined with control values that fell within expected range of values as given on the QC certificate.

Data analysis

The data obtained was analysed using Statistical Package for Social Sciences (SPSS) version 25.0 (IBM, USA). Data were coded and entered into Microsoft Excel spreadsheet and later imported into SPSS for cleaning and analysis. Descriptive statistics with the use of frequencies, percentage/proportions mean and standard deviation were used to summarise data. Inferential statistics with the use of Pearson Chi-square test (for qualitative data) and Student's t-test (for quantitative variables) were used to test for association between bivariate at 5% level of significance. Differences between mean values of antibody levels after three doses DPT between the different age groups were compared using the t-test. Linear regression analysis was performed to determine the predictors of antibody response in the two groups. A value of P < 0.05 was considered statistically significant. A multivariable linear regression model was used to control for the effect of possible confounders and identify independent factors that have effect on changes in serum anti-tetanus IgG levels. Factors with P value of the Wald statistic <0.25 at the univariate level and those with biologic plausibility were introduced into the final multivariable model.


  Results Top


Sociodemographic characteristics of study participants

Age and sex distribution of the study participants

A total of 418 children aged 6–60 months participated in the study. Out of these, 219 (52.4%) were male while 199 (47.6%) were female, giving a male: Female ratio of 1.1:1. The mean age of study participants was 24.7 ± 16.1 months (t = 0.71; P > 0.05).

Age distribution of participants in the groups of vaccine types (diphtheria-pertussis-tetanus or pentavalent)

The children who had received plain DPT were in Group 1 while those who had received the pentavalent vaccine were in Group 2. Those in Group 1 were individuals above 29 months while those below 29 months were in Group 2. However, one child aged 40 months who relocated from Ibadan to Calabar, had received the pentavalent vaccine and was added in Group 2.

[Table 2] shows the sociodemographic distribution of children in the two groups. Out of the 418 study participants, 130 (31.1%) were in Group 1 and 288 (68.9%) were in Group 2. The mean age of those in Group 1 was 44.1 ± 9.5 months while that of the patients in Group 2 was 15.9 ± 7.5 months (t = 1.0; P = 0.00).
Table 2: Age distribution of the study participants in vaccine type groups

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Mean antibody levels to tetanus toxin of grouped subjects

[Table 3] shows the mean antibody levels to tetanus toxin in patients who had received three doses of either DPT or pentavalent vaccines in early infancy. Overall, the mean value was 1.0 ± 0.9 IU/ml (Range: 0.0–4.1). The mean value for patients in Group 1 was 1.2 ± 1.0 IU/ml while that of children in Group 2 was 0.9 ± 0.8 IU/ml (t = 3.6; P = 0.003). The mean IgG values had standard deviations more than a third of the mean. Thus, we moved on to further analysis using the Wilcoxon rank sum (Mann–Whitney U-test. The median (interquartile range) level of IgG in Group 1 was 1.1 (0.4–1.8) and that of the patients in Group 2 was 0.6 (0.4–1.4) (P = 0.006).
Table 3: Mean antibody levels to tetanus toxin of grouped patients

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Proportion of study participants with protective levels of antibody

[Table 4] depicts the proportion of the study participants in each group with protective antibody levels (≥0.1 IU/ml). All the proportions were above 90%. The proportion of those in Group 1 with protective anti-tetanus IgG levels was 93.9% while that of subjects in Group 2 was 96.5%. In addition, the proportion of unprotected patients in Group 1 was 6.2% while that of the group was 3.5%. The difference in proportion was not statistically significant (P = 0.21).
Table 4: Proportion of the study participants with protective antibody levels ≥0.1 IU/ml

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Predictors of variability in anti-tetanus immunoglobulin G levels

[Table 5] illustrates that for every 1 month increase in age, there was a 0.013 (95% Confidence interval: 0.003–0.023) unit increase in tetanus IgG levels after adjusting for the effect of vaccine type, gender and social class. There was no significant difference in the IgG levels of the patients in both vaccine groups after adjusting for gender and social class (P = 0.79).
Table 5: Linear regression models showing independent associations with changes in anti-tetanus IgG levels

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  Discussion Top


Immunity to tetanus toxin is induced only by immunisation and is antibody-mediated.[20] It is important to note that the potency of a vaccine plays a role in the immunity acquired.[21] Seroepidemiological studies have been convincingly advocated.[8] Many countries have moved from the use of plain DPT vaccine type to the use of the pentavalent vaccine. However, there are hardly any studies that determined the effectiveness of the pentavalent vaccine compared to the plain DPT vaccine.

This study showed that the proportion of vaccines with protective anti-tetanus antibody levels who had received the plain DPT vaccine was 93.9% and 96.5% for the pentavalent group. Both were above 90%. It is therefore apparent that both vaccines were sufficient in maintaining protection in above 90% of vaccines.

Overall, both vaccines provided a protective antibody level against tetanus in 95.7% of the total study population. This prevalence was similar to 99.6% recorded by Gergen et al.[22] in Mexican American children aged 4–11 years. However, in that study, all the children were given plain DPT vaccine. Orimadegun et al.[16] in a study in south west Nigeria, had a lower proportion of protected patients of 44.7%, although, the patients were older, the author did not also compare the two vaccine groups. Among the first Asian countries to introduce pentavalent vaccine into their immunisation schedules, the effectiveness of the pentavalent vaccine was not compared with plain DPT, rather Deshpande and Ghongane[23] compared two pentavalent vaccines from two different manufacturers.

The proportion of those protected using the pentavalent vaccine in the present study was 96.5%, which was higher than the 87% and 89% documented by Deshpande and Ghongane[23] from both pentavalent vaccines compared. However, the higher proportion in the current study was similar to 98.8%–100% documented by Eregowda et al.,[24] Sharma et al.[25] and Schmid et al.[26] They all demonstrated, in agreement with the present study, that the pentavalent vaccine is highly immunogenic though none of the three studies compared it with the plain DPT vaccine. Oli et al.[27] did not compare but grouped them and showed that both plain DPT and the pentavalent vaccine had 100% immunogenicity (demonstrated in animals). This is in line with the findings of the present study too. Kanra et al.[28] compared pentavalent vaccine with DPT-Hib and HBV separate combination (not plain DPT) but the author demonstrated non-inferiority of pentavalent vaccine to the separately administered DPT-Hib and HBV vaccine. This is similar to the findings in the present study both vaccines were effective, and none was inferior to the other.

This study revealed that those in the older age group received the plain DPT vaccine (Group 1) in early infancy while those in the younger age group received the pentavalent vaccine (Group 2). The mean anti-tetanus IgG antibodies of those who had the pentavalent vaccine were significantly lower than that of those who had received plain DPT. This was in terms of absolute values. With detailed analysis using the t- test, the IgG levels were not normally distributed and further analysis using the Wilcoxon rank sum test was done. This still showed that the median values of anti-tetanus IgG in circulation for those who received pentavalent vaccine were significantly lower than that found in those who used the plain DPT vaccine.

With further analysis, the only predictor of variability in anti-tetanus antibody levels was age, with the older children (who had mainly DPT) having higher values. For every 1 month increase in age, there was a 0.013 unit (IU/ml) increase in anti-tetanus IgG levels. However, since at the multivariate level only age, and not type of vaccine, predicted variability in antibody level, the difference may be due to exposure of the older children to sub-clinical tetanus which further boosted antibody levels. Gender and social class were not predictors. This is in contrast to the findings of Orimadegun et al.[16] who found age and gender as predictive factors for nonprotective levels of immunity for after DPT vaccination.

This is probably the first paper that has compared the effectiveness of DPT compared to the pentavalent vaccine. Although, Ali et al.[29] showed that there was a fivefold increase in the absolute value of anti-tetanus antibodies in circulation post-immunisation with the pentavalent vaccine, he did not compare with those who had received plain DPT vaccine.

This, however, was a cross-sectional study therefore unable to explore the rate of possible decay of antibodies particularly beyond the age group studied.


  Conclusion Top


While the median levels of anti-tetanus IgG was higher for the DPT than the pentavalent group, most probably due to sub-clinical exposure to tetanus of the older children who took DPT rather than the type of vaccine, the proportion of children that had protective levels of antibodies is equal for both vaccines. The continued use of the pentavalent vaccine is therefore recommended. Further studies may be required to determine the rate of decay following the use of both vaccines.

Acknowledgement

We would like acknowledge the doctors in the department of Paediatrics who assisted in the collection of the data.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

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    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5]



 

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