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Contents lists available at ScienceDirect
Vaccine
jou rnal homepage: www.elsevier.com/locate/vaccine
Survey of poliovirus antibodies in Kano, Northern Nigeria
a b c d
Zubairu Iliyasu , Eric Nwaze , Harish Verma , Asani O. Mustapha , Goitom
e e f f
Weldegebriel , Alex Gasasira , Kathleen A. Wannemuehler , Mark A. Pallansch ,
a b,g c,∗
Auwalu U. Gajida , Muhammad Pate , Roland W. Sutter
a
Department of Community Medicine, Aminu Kano Teaching Hospital & Bayero University, Kano, Nigeria
b
National Primary Health Care Development Agency, Abuja, Nigeria
c
World Health Organization, Geneva, Switzerland
d
Department of Pediatrics, Aminu Kano Teaching Hospital & Bayero University, Kano, Nigeria
e
World Health Organization, Abuja, Nigeria
f
Centers for Disease Control and Prevention, Atlanta, GA, United States
g
Duke Global Health Institute, Duke University, Durham, USA
a r t i c l e i n f o a b s t r a c t
Article history: Introduction: In 1988, the World Health Assembly resolved to eradicate poliomyelitis. Since then, much
Received 11 April 2013
progress towards this goal has been made, but three countries including Nigeria remain polio-endemic
Received in revised form 15 August 2013
as of end 2012. To assess the immunity level against poliomyelitis in young children in Northern Nigeria,
Accepted 21 August 2013
we conducted a seroprevalence survey in the Kano Metropolitan Area (KMA) in May 2011.
Available online xxx
Methods: Parents or guardians of infants aged 6–9 months or children aged 36–47 months presenting to
the outpatient department of Murtala Mohammad Specialist Hospital were approached for participation,
Keywords:
screened for eligibility and were asked to provide informed consent. After that, a questionnaire was
Poliomyelitis
Seroprevalence administered and blood was collected for neutralization assay.
Kano Results: A total of 327 subjects were enrolled. Of these, 313 (96%) met the study requirements and
Nigeria were analyzed (161 [51%] aged 6–9 months and 152 [49%] aged 36–47 months). Among subjects aged
Oral poliovirus vaccine 6–9 months, seroprevalence was 81% (95% confidence interval [CI] 75–87%) to poliovirus type 1, 76%
(95% CI 68–81%) to poliovirus type 2, and 73% (95% CI 67–80%) to poliovirus type 3. Among subjects aged
36–47 months, the seroprevalence was 91% (95% CI 86–95%) to poliovirus type 1, 87% (95% CI 82–92%)
for poliovirus type 2, and 86% (95% CI 80–91%) to poliovirus type 3. Seroprevalence was associated with
history of oral poliovirus vaccine (OPV) doses, maternal education and gender.
Conclusions: Seroprevalence is lower than required levels for poliovirus interruption in the KMA. Per-
sistence of immunity gaps in the 36–47 months group is a big concern. Since higher number of vaccine
doses is associated with higher seroprevalence, it implies that failure-to-vaccinate and not vaccine failure
accounts for the suboptimal seroprevalence. Intensified efforts are necessary to administer polio vaccines
to all target children and surpass the threshold levels for herd immunity.
Published by Elsevier Ltd.
1. Introduction challenges to eradicating poliomyelitis in the remaining endemic
countries include inadequate service delivery of oral poliovirus vac-
Over two decades have passed since the World Health Assem- cine (OPV) and suboptimal OPV efficacy in the densely populated
bly resolved in 1988 to eradicate poliomyelitis by 2000 [1], and tropical reservoirs [4,5].
great strides have been made towards achieving this goal. In 2012, Nigeria is the only country in the world that is simultaneously
the number of polio-endemic countries was reduced from 125 to endemic for wild poliovirus types 1 and 3 and circulating vaccine-
only 3 (i.e., Afghanistan, Pakistan and Nigeria) [2] and the inci- derived poliovirus type 2 (cVDPV2) [6,7]. Trivalent OPV (tOPV) was
dence of poliomyelitis decreased by more than 99% [3]. The main exclusively used for polio eradication in Nigeria initially, followed
by the introduction of more immunogenic polio vaccines in sup-
plementary immunization activities (SIAs), including monovalent
OPV (mOPVs) in 2006 and bivalent (types 1 and 3) OPV (bOPV) in
∗
Corresponding author at: Research Policy and Product Development, Polio Erad-
2010 [8,9].
ication Initiative, World Health Organization, 20, avenue Appia-1211, Geneva 27,
Nigeria’s polio control problems got aggravated in 2003, when
Switzerland. Tel.: +41 22 791 46 82; fax: +41 22 791 1571.
E-mail address: [email protected] (R.W. Sutter). despite having the highest number of polio cases in the world,
0264-410X/$ – see front matter. Published by Elsevier Ltd.
http://dx.doi.org/10.1016/j.vaccine.2013.08.060
Please cite this article in press as: Iliyasu Z, et al. Survey of poliovirus antibodies in Kano, Northern Nigeria. Vaccine (2014), http://dx.doi.org/10.1016/j.vaccine.2013.08.060
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Fig. 1. Northern Nigeria Map showing polio cases in Kano and KMA from 2008–2011.
planned SIAs were suspended in some northern states because serosurveys conducted elsewhere (i.e., India, Pakistan, Egypt).
of OPV safety concerns [10]. Rumors circulated that the vaccine Regarding the immunity profile, infants (i.e., 6–9 months) would
was deliberately tampered with anti-fertility agents and human be expected to have the lowest immunity profile because they
immunodeficiency virus (HIV) [11]. Consequently, the number of have by-and-large lost maternally derived antibodies against
poliomyelitis cases in Nigeria increased to 1122 in 2006. This case polioviruses and might not have received sufficient doses of polio
count dropped to 285 polio cases in 2007 but in 2008, the number vaccine to have very high seroprevalence. The older age group
of cases rebounded to 798. Following renewed efforts a downward (36–47 months) with potentially higher vaccine and secondary
trend started and was sustained throughout 2010 [2,3]. exposure is expected to have very high immunity in areas that
However, in 2011 and 2012, there was a relative upsurge of wild have interrupted or are close to interruption of poliovirus trans-
poliovirus cases in Nigeria with 62 cases in 2011 and 122 in 2012 mission. Regarding the comparability with other serosurveys, this
(WHO unpublished data, as of 2 April 2013). All northern states gives us a sense of how far KMA still has to go in terms of interrupt-
remain endemic, including the most populous Kano state which ing transmission. The selection of age groups also had relevance to
reported 28 wild poliovirus cases and 3 cVDPV2 cases in 2012 (WHO the epidemiology of poliomyelitis cases in endemic areas, where
unpublished data, as of 2 April 2013). In addition, cVDPV2 was approximately 75% cases were in children <3 years of age.
repeatedly detected in sewage samples collected through environ-
mental surveillance in the state. 2.3. Selection of the study area
Although there are some published reports [12–16] of sero-
prevalence studies in Nigeria, this study in Kano was undertaken Kano state and KMA within the state was selected for seropreva-
by the Global Polio Eradication Initiative (GPEI) partners and the lence primarily due to high incidence of polio cases in the recent
Nigeria national government to provide an immunity benchmark years of all three serotypes (i.e., wild poliovirus types 1 and 3, and
to reflect program performance and to guide future program action. cVDPV2). KMA comprised of eight local government areas (LGAs):
Kano Municipal, Fagge, Nassarawa, Dala, Gwale, Tarauni, Ungogo
and Kumbotso. So the study area was representative of the north-
2. Methods
ern Nigeria with endemic poliovirus transmission. Location of Kano
state and KMA within the state can be seen in the northern Nigeria
2.1. Study objectives
map (Fig. 1) showing polio cases (as wild poliovirus (WPV) cases)
from 2008–2011.
The objectives of this study were: (1) to assess the seropreva-
lence to poliovirus type 1, type 2 and type 3 among infants aged 6–9
2.4. Routine and SIA doses
months and children aged 36–47 months in the Kano Metropolitan
Area (KMA) of Nigeria; and (2) to evaluate specific risk factors for
In this area, routine immunization (RI) doses of trivalent OPV
low seroprevalence.
(tOPV) are given at birth, 6, 10, 14 weeks and multiple SIAs are
implemented every year with bOPV or tOPV wherein all children
2.2. Study design and its rationale up to 5 years are expected to receive additional OPV dose every
time. The study participants could have received up to 4 routine
Health facility based design was preferred over population- doses and a variable number of SIA doses depending on age of the
based survey. Since there is resistance to polio vaccination in this child and completeness of coverage in SIA. A total of 8 SIAs includ-
area, the health facility based design had a better possibility of ing one partial (not covering all LGAs of KMA) were conducted in
including both those accepting and refusing vaccination; and in Kano State from July 2010 (starting age for 6–9 months cohort)
addition provided an operational advantage in this area. to May 2011 (start of survey), 5 using bOPV and 3 using tOPV.
The choice of the age groups was based on two factors: (a) Therefore 6–9 month infants could have received 3–5 bOPV and
expected immunity profile; and (b) comparability with other 2–3 tOPV doses through SIAs since birth.
Please cite this article in press as: Iliyasu Z, et al. Survey of poliovirus antibodies in Kano, Northern Nigeria. Vaccine (2014), http://dx.doi.org/10.1016/j.vaccine.2013.08.060
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Table 1
Demographic and other attributes of study population, Kano Metropolitan Area,
Northern Nigeria, 2011.
N (%)
Attribute Age Age
6–9 months 36–47 months
n = 161 n = 152
Gender
Male 79/159 (49.7) 83/149 (55.7)
Female 80/159 (50.3) 66/149 (44.3)
Mother’s education
Primary or less 84/160 (52.5) 94/152 (61.8)
Secondary or tertiary 76/160 (47.5) 58/152 (38.2)
No. of children aged <5 years
in household
1–2 118/157 (75.2) 124/152 (81.6)
>2 39/157 (24.8) 28/152 (18.4) Fig. 2. Seroprevalence and 95% confidence intervals, by poliovirus serotype and age
Wasting group, Kano metropolitan Area, Northern Nigeria, 2011.
1 – no 129/155 (83.2) 120/148 (81.1)
2 – moderate 18/155 (11.6) 22/148 (14.9)
3 – severe 8/155 (5.2) 6/148 (4.1) 2.8. Enrollment and survey procedures
Stunting
1 – no 76/148 (51.4) 78/145 (53.8)
Enrollment started on 19 May and was completed on 2 June
2 – moderate 34/148 (23.0) 38/145 (26.2)
2011. Parents and guardians of patients visiting the pediatric
3 – severe 38/148 (25.7) 29/145 (20.0)
OPD of MMSH were approached for possible participation of their
Routine OPV doses
0 18/143 (12.5) 27/121 (22.3) infants/children in this survey. Initial screening for age and area
1 14/143 (9.7) 5/121 (4.1)
of residence was done by a study staff in OPD. Patients potentially
2 27/143 (18.8) 12/121 (9.9)
fulfilling the age and residence criteria were directed to the study
3 39/143 (27.1) 23/121 (19.0)
clinic in the same order as they became available from the OPD. The
4 46/143 (31.9) 54/121 (44.6)
SIAs OPV doses physician in the study clinic explained the study to the parents or
0 31/155 (20.0) 5/148 (3.4) guardians and assessed children for inclusion criteria. After obtain-
1–3 69/155 (44.5) 26/148 (17.6)
ing informed consent of caretakers, weight and length/height were
4–6 53/155 (34.2) 31/148 (21.0)
≥ measured, immunization history was taken and the questionnaire
7 2/155 (1.3) 86/148 (58.1)
was completed.
Total doses (RI and SIAs)
0 6/139 (4.3) 3/136 (2.2)
1–3 36/139 (25.9) 10/136 (7.4)
2.9. Blood collection and antibody testing procedures
4–6 50/139 (36.0) 17/136 (12.5)
≥7 47/139 (33.8) 106/136 (77.9)
One ml of blood was collected through venipuncture. At the end
of the study, sera were shipped to the Centers for Disease Con-
2.5. Selection of study site trol and Prevention (CDC) in Atlanta. Sera were tested in triplicate
for levels of neutralizing antibody titers against poliovirus types 1,
Murtala Mohammad Specialist Hospital (MMSH) was selected 2 and 3, respectively, using modified micro-neutralization assays
as the study site because it is the largest pediatric hospital in KMA. [17,18]. For seroprevalence, antibody titers >1:8 were regarded as
This public sector hospital has a very high turnover of the patients positive.
in the outpatient department (OPD). Patients come from a wide
catchment area including our area of interest i.e. 8 LGAs of KMA and 2.10. Definitions
include a large percentage from the lower socio-economic section
of the population. History of OPV doses received by the study subjects was based
on verbal recall because immunization cards were not available
2.6. Sample size with most parents. RI and SIA doses were separately recorded. Total
vaccine doses were the sum of routine and SIA doses. Doses were
A total of 300 children were required for the study. Sample size included regardless of how close they were in time to other doses.
calculations were based on 20% presumed difference in seropreva- Nutritional status was measured using height, weight and age. Data
lence between the two age groups. Considering a seroprevalence were compared to the standard distribution of a reference popula-
for poliovirus types 1, 2 and 3 of 40–60% and applying a power tion using Epi Info software [19]. The reference population was the
of 0.90 (beta) and alpha of 0.05 (two-tailed test), the sample size CDC’s National Center for Health Statistics Standard recommended
came to 135 per arm. This was inflated to 150 per arm to account for international use by UNICEF and WHO [20]. Categories of mal-
for possible exclusions. nutrition were based on standard deviation (SD) units (z-scores)
below the mean of the reference population. These categories were
2.7. Eligibility criteria defined as normal (<2 SD), severe to moderate (2.0–2.9 SD) and
extreme (≥3 SD). Stunting (low height-for-age) is a measure of
Infants aged 6–9 months or children 36–47 months living at chronic malnutrition; wasting (low weight-for-height) is a measure
least for one month in any of the eight LGA areas of KMA with of acute malnutrition.
consenting care-givers were eligible to participate, except those
with (a) contraindication to venepuncture; (b) serious acute illness 2.11. Data management and statistical analysis
requiring hospitalization; or (c) diagnosed or suspected congenital
immunodeficiency disorder in the subject or an immediate family Questionnaires were double-entered into an initial database
member. using Epi Info software [19]. Data analysis was done using SAS
Please cite this article in press as: Iliyasu Z, et al. Survey of poliovirus antibodies in Kano, Northern Nigeria. Vaccine (2014), http://dx.doi.org/10.1016/j.vaccine.2013.08.060
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Table 2
Seroprevalence among subjects aged 6–9 months, by demographic or other attributes, Kano Metropolitan Area, Northern Nigeria, 2011.
No. of children Seroprevalence to poliovirus
Type 1 Type 2 Type 3
n (%) n (%) N (%)
Genderd
Male 79 68 (86.1) 62 (78.5) 59 (74.7)
Female 80 60 (75.0) 56 (70.0) 57 (71.3) d,b,c
Mother’s education
Primary or less 84 64 (76.2) 56 (66.7) 54 (64.3)
Secondary/tertiary 76 65 (85.5) 63 (82.9) 63 (82.9)
d
No. of children <5 years in household
1–2 118 94 (79.7) 83 (70.3) 84 (71.2)
>2 39 32 (82.1) 33 (84.6) 30 (76.9)
Wastinge
1 – no 129 105 (81.4) 96 (74.4) 95 (73.6)
2 – moderate 18 15 (83.3) 15 (83.3) 15 (83.3)
3 – severe 8 6 (75.0) 5 (62.5) 4 (50.0)
Stuntinge
1 – no 76 64 (84.2) 60 (79.0) 57 (75.0)
2 – moderate 34 28 (82.4) 24 (70.6) 26 (76.5)
3 – severe 38 29 (76.3) 26 (68.4) 24 (63.2)
e,a,b,c
Routine OPV doses
0 18 10 (55.6) 7 (38.9) 5 (27.8)
1 14 12 (85.7) 8 (57.1) 7 (50.0)
2 27 19 (70.4) 18 (66.7) 21 (77.8)
3 39 34 (87.2) 35 (89.7) 34 (87.2)
4 46 41 (89.1) 40 (87.0) 39 (84.8)
e,a,b,c
SIAs OPV doses
0 31 19 (61.3) 20 (64.5) 18 (58.1)
1–3 69 55 (79.7) 46 (66.7) 49 (71.0)
b
≥4 55 50 (90.9) 48 (87.3) 46 (83.6)
e,a,b,c
Total doses (RI and SIAs)
0 6 3 (50.0) 1 (16.7) 0 (0)
1–3 36 24 (66.7) 21 (58.3) 20 (55.6)
4–6 50 40 (80.0) 38 (76.0) 39 (78.0)
≥747 44 (93.6) 43 (91.5) 43 (91.5)
a
Covariate significantly associated with seropositivity to Type 1 for ˛=0.05.
b
Covariate significantly associated with seropositivity to Type 2 for ˛=0.05.
c
Covariate significantly associated with seropositivity to Type 3 for ˛=0.05.
d
Pearson Chi-square test.
e
Cochrane-Armitage test for trend.
version 9.2 by CDC, Atlanta [21]. Chi-square tests were used to characteristics, nutritional indices and routine and SIA OPV dose
assess the association between dichotomous predictors and sero- histories are shown in Table 1.
prevalence and dichotomous predictors and number of doses.
Cochrane-Armitage test for trend was used to test for trend in
3.3. Seroprevalence
seroprevalence across sub-groups of ordinal variables. Logistic
regression was used to estimate adjusted odds ratios and assess
The overall seroprevalence levels for poliovirus types 1, 2 and
the association of other risk factors (gender, education level, nutri-
3 poliovirus were 81% (95% confidence intervals [CI] 75–87%),
tion, etc.) on seroprevalence by number of vaccine doses received
75% (95% CI 68–81%) and 73% (95% CI 66–80%) respectively in
among children 6–9 months. All risk factors were considered in the
the 6–9-month age group and 91% (95% CI 86–95%), 87% (95% CI
models; only those with a type III p-value <0.10 were included in
81–92%) and 86% (95% CI 80–91%) in the 36–47-month age group
the final model.
[Fig. 2]. Seroprevalence is significantly higher in the older age
group for each type. The chi-square p-values are 0.01, 0.006, and
3. Results 0.008.
3.1. Recruitment, exclusions and final study sample
3.4. Risk factors
Total of 327 subjects were enrolled. 14 subjects were excluded
In the 6–9 months age group, the univariate analysis (Table 2)
due to insufficient data or samples, leaving 313 for analysis;
showed significant association of seroprevalence of all the three
161 (51%) in the 6–9 months age group and 152 (49%) in the
types with the number of routine, SIA and the total OPV doses
36–47 month age group. Subjects were included from all eight LGAs
received. For types 2 and 3, there was also a significant association
in KMA.
between mother’s educational status and seropositivity. Although
male gender tended to have higher seroprevalence for the three
3.2. Characteristics of study subjects types, these differences were not statistically significant. Only 96
(60%) out of 161 infants were seropositive to all 3 serotypes and 16
The median ages were 8 and 41 months in 6–9 months (10%) to none. Out of the 16 infants that were seronegative to all
and 36–47 months age groups respectively. The demographic 3 types, 11 received less than 4 OPV doses, 12 had mothers with
Please cite this article in press as: Iliyasu Z, et al. Survey of poliovirus antibodies in Kano, Northern Nigeria. Vaccine (2014), http://dx.doi.org/10.1016/j.vaccine.2013.08.060
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Table 3
Seroprevalence among subjects aged 36–47 months, by demographic or other attributes, Kano Metropolitan Area, Northern Nigeria, 2011.
No. of children Seroprevalence to poliovirus
Type 1 Type 2 Type 3
d,b
Gender n (%) n (%) n (%)
Male 83 76 (91.6) 77 (92.8) 69 (83.1)
Female 66 59 (89.4) 53 (80.3) 58 (87.9) d,b
Mother’s education
Primary or Less 94 86 (91.5) 77 (81.9) 77 (81.9)
Secondary/Tertiary 58 52 (89.7) 55 (94.8) 53 (91.4)
d
No. of children<5 years. in household
1–2 124 113 (91.3) 110 (88.7) 106 (85.5)
>2 28 25 (89.3) 22 (78.6) 24 (85.7)
Wastinge
1 – no 120 109 (90.8) 107 (89.2) 103 (85.8)
2 – moderate 22 19 (86.4) 17 (77.3) 18 (81.8)
3 – severe 6 6 (100) 5 (83.3) 5 (83.3)
Stuntinge
1 – no 78 72 (92.3) 70 (89.7) 67 (85.9)
2 – moderate 38 32 (84.2) 31 (81.6) 30 (79.0)
3 – severe 29 27 (93.1) 25 (86.2) 26 (89.7)
e,b
Routine OPV doses
0 27 23 (85.2) 19 (70.4) 21 (77.8)
1 5 4 (80.0) 4 (80.0) 2 (40.0)
2 12 12 (100) 10 (83.3) 9 (75.0)
3 23 20 (87.0) 23 (100) 21 (91.3)
4 54 51 (94.4) 48 (88.9) 47 (87.0)
e,a,c
SIAs OPV doses
0 5 4 (80.0) 4 (80.0) 4 (80.0)
1–3 26 22 (84.6) 21 (80.8) 18 (69.2)
4–6 31 27 (87.1) 26 (83.9) 26 (83.9)
≥7 86 82 (95.4) 77 (89.5) 78 (90.7)
e,a,b,c
Total doses (RI and SIAs)
0 3 2 (66.7) 2 (66.7) 2 (66.7)
1–3 10 8 (80.0) 6 (60.0) 5 (50.0)
4–6 17 14 (82.4) 16 (94.1) 14 (82.4)
≥7 106 100 (94.3) 94 (88.7) 93 (87.7)
a
Covariate significantly associated with seropositivity to Type 1 for ␣=0.05
b
Covariate significantly associated with seropositivity to Type 2 for ␣=0.05
c
Covariate significantly associated with seropositivity to Type 3 for ␣=0.05
d
Pearson Chi-square test
e
Exact Cochrane-Armitage test for trend
primary education or less and 9 had moderate to severe stunting. had secondary or tertiary education had ≥4 total doses compared
There was an association between mother’s education and total to 85% whose mother had primary school or less (p-value 0.06).
doses received. Subjects whose mothers had secondary or tertiary In the logistic regression analysis, Table 4 shows that for infants
education tended to have more total doses of OPV (83% vs. 57% with aged 6–9 months, RI and SIA doses remained significant predictors
≥
4 doses; p-value = 0.002). of seropositivity to poliovirus. Each additional RI dose increased the
In the 36–47 months age group, the univariate analysis (Table 3) odds of seropositivity to type I poliovirus by nearly half (OR = 1.48;
also showed significant association between seropositivity to all 95% CI 1.09–2.01). Similarly, subjects that received one dose of
the three serotypes with the number of the total OPV doses SIA had a three-fold increased odds of being seropositive against
received. Types 1 and 3 seropositivity was associated with SIA poliovirus type 1 (OR = 3.00; 95% CI 1.17–7.70). For type 2, odds
doses; type 2 was associated with routine OPV doses. For type 2, ratio for each additional RI dose is 1.87 (OR 1.87; 95% CI 1.38–2.53)
there was also a significant association between mother’s educa- and for one SIA dose is 1.74 (OR 1.74; 95% CI 0.67–4.51). For type
tional status and seropositivity. Only 112 (60%) out of 152 were 3, each additional RI dose increased the odds of seropositivity by
seropositive to all 3 serotypes and 4 (3%) were seronegative to all a factor of 2 (OR = 2.02; 95% CI 1.48–2.76), and at least one dose
three. In older children, 94% of males had ≥4 total doses compared during an SIA resulted in nearly three times higher odds (OR = 2.62;
to 86% of females (p-value = 0.06); 98% of children whose mothers 95% CI 1.01–6.82).
Table 4
Predictors of seropositivity among subjects aged 6–9 months, Kano Metropolitan Area, Northern Nigeria, 2011.
a
Type 1 (n = 139) Comparison Odds Ratio Lower 95% CI Upper 95% CI Type III p value
RI Dose (continuous) Each additional dose 1.48 1.09 2.01 0.013
Any campaign dose ≥1 SIA dose v. 0 SIA doses 3.00 1.17 7.70 0.022
Type 2 (n = 136)
RI Dose (continuous) Each additional dose 1.87 1.38 2.53 <0.001
Any campaign dose ≥1 SIA dose v. 0 SIA doses 1.74 0.67 4.51 0.253
Type 3 (n = 139)
RI dose (continuous) Each additional dose 2.02 1.48 2.76 <0.001
Any campaign dose ≥1 SIA dose v. 0 SIA doses 2.62 1.01 6.82 0.048
a
Type III Chi-square p-value is a test of a predictor’s overall significance after adjusting for other predictors in the model.
Please cite this article in press as: Iliyasu Z, et al. Survey of poliovirus antibodies in Kano, Northern Nigeria. Vaccine (2014), http://dx.doi.org/10.1016/j.vaccine.2013.08.060
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4. Discussion augment population immunity in Northern Nigeria in order to
interrupt transmission of all three circulating poliovirus serotypes
Our survey confirms that substantial immunity gaps to all three and achieve eradication.
polioviruses exist in the study populations in the KMA in northern Historically serial seroprevalence surveys served as a useful
Nigeria. Despite intensive efforts over the years to improve the vac- monitoring tool in polio endemic countries, so we intend to peri-
cination coverage, the prevalence of antibodies against polioviruses odically repeat the survey in KMA to assess trends in immunity and
remains at levels that are insufficient to interrupt poliovirus trans- indirectly the program performance. Though the community level
mission. acceptance for vaccination is erratic in the area, we observed a good
The low seroprevalence among 6–9-month old reflects the parental response for participation in seroprevalence survey in this
current programmatic gaps, while the low seroprevalence in health facility based survey. So we plan to follow a similar design
36–47 month children reflects a longstanding sub-optimal vacci- for the follow-up surveys.
nation and a possible future problem. The seroprevalence levels
are much lower than in corresponding serosurveys in Egypt and Acknowledgements
India [22,23].
Nevertheless, in both age groups evaluated, an increasing num-
We acknowledge the contributions of Drs Safiya Gambo, Hal-
ber of routine and SIA doses resulted in increasing levels of
ima Adamu and Yunusa Sanusi (Research Physicians), Nasiru
seroprevalence. Having received >7 total doses of polio vaccine pro-
Magaji Sadiq, Amina Ibrahim Muhammad (Laboratory Scien-
vided >90% seroprevalence to poliovirus type 1 in both age groups.
tists/Phlebotomists) and Matron Hadiza Umar (Research Nurse) to
This confirms the effectiveness of OPV in inducing immunity in
the successful conduct of this survey. We recognize the contrib-
these populations.
utions of Debbie Moore and Yiting Zhang in performing the serology
In terms of risk factors other than low vaccination histories,
tests at CDC Atlanta. We also acknowledge the support provided
lower seroprevalence was associated with female gender, lower
by the Kano State Government, the management and staff of Mur-
maternal education, and having fewer children in the household.
tala Mohammad Specialist Hospital and the Kano State WHO polio
While maternal education and fewer children in the household are
office staff. Funding: Provided by the World Health Organization.
probably not amenable to immediate intervention, social commu-
Conflict of interest: No authors reported a conflict of interest
nication strategies could address the gender difference of 11% to
type 1 seropositivity in the 6–9 month age group.
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