EVALUATION OF THE IMMUNE RESPONSE TO POLIO VACCINE IN MALNOURISHED CHILDREN IN SANA'A CITY

This study was made to evaluate the immune response to polio virus vaccine among PEM children by measuring the level of circulating Immunoglobulin G (IgG) antibodies against polio virus (IgG-PV) after immunization with the primary series of POV, and determining the coverage rate of universal childhood vaccine for polio virus. A cross-sectional laboratory study was conducted in Department of Medical Microbiology and Clinical Immunology, Faculty of Medicine and Health Sciences, and Al-Sabeen University Hospital, Sana’a University. A total of 279 PEM children were selected and investigated for universal childhood vaccination coverage rate for polio vaccine. Blood samples were collected from all, then tested for levels of IgG-PV by ELISA method. For assessment IgG-PV levels more than 10 units/ml were considered protected against polio virus infection. The coverage rate of polio virus vaccine for first year vaccine was 96.8%; and 91.1% of vaccinated PEM children responded to the vaccine with mean level of 46.2 U/ml. A statistically significant difference was observed with respect to sero-protective IgGPV between males and females (85.7% and 94.1% respectively, p=0.002); and older children (>37 months) (97.7%). We conclude that a small proportion of malnourished vaccinated children with a normal immune status were not serologically immune to polio virus infection, and remain to be reconsidered for either revaccination or booster doses due to lack of or inadequate response. PEM group gave slightly reduced response to OPV hence there is need to give this group IPV (injectable polio vaccine) along with OPV and different micro-nutrition deficiencies like Zinc and iron.


INTRODUCTION
Globally malnutrition is the most important cause for failure of all vaccination 1,2 . Consistent with Independent Monitoring Board of the Global Polio Eradication Initiative, Tenth Report 2014 on 28th of October 2014, globally 257 polio cases were reported in three polio endemic countries, of which 220, wild polio cases were reported from Pakistan 2,3,4 . About 165 million children are universally, chronically malnourished. This preventable state has affected one in every four children. Malnutrition cause 2.3 million children deaths per year, an average of one death per every 15 seconds 5 . According to WHO majority of expected malnourished children live in developing countries. Less than 30% of them are under the age of five years and half of them are suffering from PEM 1,2 .
The report of MHP Yemen, and UNICEF shows the PEM is very high in Yemen among children (50%) this Malnutrition might be one of the main difficulty for polio eradication among under five years old children in Yemen 6 . In its 41 st meeting in 1988, World Health Assembly approved a declaration according to which "OPV is exclusively used worldwide for polio eradication for some reasons. It is cheaper than Intramuscular polio Vaccine (IPV) and can be easily orally administered" 2 . However, worldwide, the oral vaccine doesn't effectively develop immunity against polio, particularly in malnourished children 7 . Some data from WHO has also highlighted that malnutrition hinders the battle against polio because OPV produces four times less immunity in malnourished children as compared to well-nourished. Since 50% of under-five children are malnourished in Yemen, it is very difficult to eradicate polio from Yemen 6 . Therefore, priority of current study should be focused on preventing malnutrition in this group of population. This study was made to evaluate the immune response to polio virus vaccine among PEM children by measuring the level of circulating Immunoglobulin G (IgG) antibodies against polio virus (IgG-PV) after immunization with the primary series of POV, and determining the coverage rate of universal childhood vaccine for polio virus.

SUBJECTS AND METHODS Ethical Consideration
Ethical clearance for the study was taken from the Faculty of Medicine and Health Sciences Research Review Committee. A written permission was also taken from the head of the pediatric department of the Al-Sabian Hospital, Sana'a city, Yemen. Informed Consent was taken from the parents and guardians of all selected children before the questionnaire was filled in and before the blood samples were collected.

Survey procedure and Laboratory Analysis
Demographic data and other relevant information of each participant were obtained through a questionnaire. Then, about 4 ml of blood was aseptically drawn by venipuncture after swabbing the area of interest for sample collection with alcohol. The serum was then separated from the blood by allowing clotting and centrifuging. Finally, the serum samples were labeled and stored at -20ºC until processed. The polio IgG antibody ELISA test kit, manufactured and described by DEMEDITEC Diagnostic GmbH Germany, was used for the detection of specific IgG antibodies against polio in the serum of children with strict adherence to the manufacturer's instruction manual.

Study setting
The study was conducted at the pediatric department of the Al-Sabian Hospital, Sana'a city, Yemen. The Hospital was selected because it is the only teaching hospitals in Sana'a city provides health services to malnutrition children.

Study Population
Children between the age of 6 months to 59 months who attended the pediatric patient Department (PD) with PEM. These subjects of the study were taken from 17 th of March, 2017 to 17 th of September 2017 as the study population. It was ensured that they must have received first year oral polio vaccine doses and fulfill the eligibility criteria of study. A total of 279 blood samples were collected.

Sample size
The sample size was calculated by using sample size determination in health studies by WHO with 95% confidence interval and 5% level of significance with acceptable margin of error equal to 6% with PEM population in Yemen at least equal to 500 000 children. The proportions of antibodies production among malnourished subjects ("Evaluation of the response to vaccination against poliomyelitis and measles in malnourished children 8 was 59.5% in malnutrition children. The sample size was calculated to be 257 subjects. In such a small sample size, the chance of type 1 and type 2 errors are increased. To reduce these errors in the study, we increased the sample size to 279 subjects.

RESULTS
The study included 270 malnourished children (126 males and 153 females). Most of children patients were in age group 13-24 months in which they count 36.9%, followed by age group 3-12 months, in which the rate was 31.2% (Table 1). The non-protective of polio-antibodies IgG rate in children patients was 8.6%, while the protective rate of polio-antibodies IgG in them was 91.4% (Table 2).  Table 3). The susceptibility rate to polio virus infection among males was 14.3%, higher than that of females 3.9%, with OR of susceptibility to poliovirus for male equal to 4.1 times than female (p=0.002). As regard to the age, the susceptibility rates were increase in younger age groups (Table 4). Table 5 shows the associated odds ratio of susceptibility to polio virus infection with history of polio vaccine of malnourished children.
There was high susceptibility rate to polio infection with children delivery in hospital (9.1%), and history of first month illness (9.5%) and in children had mixed feeding (33.3%), but no statistical significance was observed (Table 6).   The current study seroprevalence of protective IgG antibodies for polio virus was slightly higher (94.1%) in females compared to males (85.7%), this result is different from study by Iliyasu et al.,11 in Nigeria, but similar to Donbraye et al., 12 . study in Nigeria where females had higher antibody titers for all the three serotypes. Also result of current study is similar to Baba et al., 13 in India and to Chinese study by Wang et al., 14 . also. Sex differential non-specific effects of vaccines are common in developing countries with negative non-specific effects (NSE) of inactivated vaccines more common in girls than boys in some countries, but with no differences in high income countries 16,17 . Though the general pattern is both negative and positive NSE are stronger in females 18 , a randomized controlled trial in Guinea-Bissau negated the hypothesis that mortality rates in boys would be lower if they had not received OPV 19 . The reasons why OPV uptake is slightly higher for females in current study area are unknown. Though factors such as age, gender and urban setting have no remedial solution from a public health perspective, this study indicates that response may be affected by factors that are not amenable to modification. This is important for the understanding of oral vaccine performance in lowincome countries. When we considered age groups, there was trend toward increased rate of positive protective levels of IgG antibodies against polio virus in the current study in which the higher seropositivity rate was in the older age group ( ≥37 months age group) (97.7%) and the lowest protective rate was 87.4% in 6-12 months age group ( similar to findings in previous studies in Vellore district of Tamil Nadu -Sri Lanka in which lower rate of protective antibodies rate was found in children under one years of age 20 . This could be due to a more mature immune system or to receipt of OPV doses that are not recorded in the vaccination history taken for the child. When we study the associated odds ratio of susceptibility to polio virus infection with history of polio vaccine among malnourished children in Sana'a city Yemen, there was increased rate of susceptibility for polio virus in current study among children whom not had national camping booster polio vaccine in which the rate of susceptibility was 14.6%, while the rate of susceptibility among children whom had national camping booster polio vaccine was 5.5% only ( Table 5). Result of current study is similar to previously reported studies in which increasing the number of OPV doses received by children, decreasing the susceptibility rate for polio virus; and increase the polio-seroconversion rates among children 8,11,21 .

CONCLUSION
We conclude that a small proportion of malnourished vaccinated children with a normal immune status were not serologically immune to polio virus infection, and remain to be reconsidered for either revaccination or booster doses due to lack of or inadequate response; more information, however, needs to be gathered first on the occurrence of clinical/subclinical poliomyelitis cases (morbidity and mortality) and the overall morbidity and mortality following polio vaccination. Also the rates of vaccine coverage for the routine immunization schedule of childhood vaccines were good.