Hepatitis B Surface Antigen Carrier Rate Biology Essay

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This study was done to evaluate efficacy of the hepatitis B vaccination on HBs Ag carrier rate in children with thalassemia major. It was a cohort study conducted in the Thalassemia Center attached with Pediatric unit-I, Bahawal Victoria Hospital, Bahawalpur (Pakistan) during April 2009 to April 2010. The children with thalassemia major have age less than 60 months who received more than twenty four blood transfusions and were HBs Ag negative at the time of first blood transfusion were included.

There were 196 children in the unvaccinated and 218 children in the vaccinated (vaccination done during first year of life through EPI) cohort. There were 24 children positive for HBsAg in the unvaccinated cohort giving a positivity rate of 12.24% while 2 children were positive in the vaccinated cohort giving a positivity rate of 0.92% (p value less than 0.0001) showing a significant decrease in HBs Ag positivity after vaccination

KEY WORDS:

Hepatitis B vaccine; Hepatitis B surface antigen; Cohort study; Thalassemia major

ABBREVIATIONS:

Hepatitis B surface antigen HBs Ag

Expanded Program for Immunization EPI

INTRODUCTION:

Thalassemia is a hereditary anemia which needs lifelong transfusion as a treatment. The hepatitis B virus infection is one of the most common transfusion transmitted infection. The prevalence of hepatitis B in thalassemic children receiving multiple blood transfusions had been noted as high as 20 %( 1) or even higher. Screening of blood for hepatitis B surface antigen (HBsAg) reduces but cannot eliminate hepatitis B infection probably because of window period, low titer of hepatitis B virus and infection with its variants (2). Luckily the available vaccine against hepatitis B is highly effective even when given during infancy (3). The study conducted in Alexandria, Egypt showed that the HBsAg carrier rate among children when vaccinated against hepatitis B in the first year of life was 0.8% as compared to 2.2% among non-vaccinated children when tested at aged 6 years of life (4) while another study done in a rural community in mid-western Nigeria showed that the rate of HBs Ag positivity among the vaccinated children as 1.3% compared to 4.6% among the non-vaccinated children(5). The study done in Tanzania showed that 1.7% of healthy children under 5 years vaccinated at 4, 8 and 12 weeks of life were positive for HBs Ag (6). A number of immunological defects have been described in Thalassemia Major (7) as well as iron load may also lead to an immunodeficiency condition (8). The effect of these defects on vaccine response is controversial (9, 10) while are no studies available to know the efficacy of the vaccine in reducing the HBs Ag carrier rate in thalassemic children receiving multiple blood transfusions. The purpose of this study is to evaluate efficacy of the hepatitis B vaccination on HBs Ag carrier rate in children with thalassemia major.

METHODS AND MATERIAL: This is a cohort study which was conducted in the Thalassemia Center attached with Pediatric unit-I, Bahawal Victoria Hospital, Bahawalpur (Pakistan) during April 2009 to April 2010. The study was approved by the ethical committee of the institution. Verbal consent was taken from the parents before including in the study. The children with thalassemia major having age less than 60 months, on regular follow up and received more than twenty four blood transfusions and were HBs Ag negative at the time of first blood transfusion. This cohort (vaccinated cohort) was vaccinated against hepatitis B by giving recombinant DNA hepatitis B vaccine in a dose of 10µg in the form of combined vaccine with diphtheria, tetanus and pertussis (DPT) on monthly basis for three doses through Expanded Program for Immunization (EPI) and the course was completed before first birthday. Children who were HBs Ag positive at the start of vaccination schedule or got more than three transfusions before completion of three doses of vaccine or children with incomplete data were excluded from the study.

For comparison the control cohort was taken which consisted of record of unvaccinated children with thalassemia Major (unvaccinated cohort) who underwent for HBs Ag screening before vaccination for hepatitis B during Jan 3002 to Dec 2004 and were less than 60 months at the time of screening and had received more than twenty four blood transfusions and were HBs Ag antigen negative at the time of first blood transfusion. Children with incomplete data were excluded. The ELISA method was used to detect Hepatitis B surface antigen. All the children received blood after screening for hepatitis B through Blood Bank of Bahawal Victoria Hospital Bahawalpur. The sample size was calculated by taking anticipated probability of infection among thalassemic children (P1) as 0.2 and anticipated probability of infection among children in general population as 0.05, level of precision 50% and confidence interval 95% the minimum sample required was 184 (11). The analysis of the data was done by statistical programs "Standard Deviation Calculator" available at: http://www.easycalculation.com/statistics/standard-deviation.php and "GraphPad" at: http://www.graphpad.com/quickcalcs/index.cfm. Fisher's Exact test for categorical data and t test for continuous data was used to calculate p value and p value less than 0.05 was taken as significant.

RESULTS:

There were 196 children included in the unvaccinated cohort while 218 children in the vaccinated cohort. The characteristics of the two cohorts are shown in table-I showing that both the groups are similar.

There were 24 children positive for HBsAg in the unvaccinated cohort giving a positivity rate of 12.24% while 2 children were positive for HBsAg in the vaccinated cohort giving a positivity rate of 0.92% (p value less than 0.0001) showing significant decrease in HBs Ag positivity after vaccination

TABLE-I CHARACTERISTICS OF THE TWO COHORT

Characteristic

Vaccinated cohort

Total 218

Unvaccinated cohort

Total 196

P value

Age in months mean

SD

44.44

8.639

42.86

8.440

0.1564

Total girls

69

44

0.1564

Number of blood transfusions mean

SD

35.14

8.557

33.61

8.145

0.0638

DISCUSSION:

This is the first study conducted in the world to know the effectiveness of hepatitis B vaccination if giving through EPI in reducing the HBs Ag carrier rate in thalassemic children receiving multiple blood transfusions. The Hepatitis B vaccination starts at minimum of six weeks of age through EPI in Pakistan.The HBs Ag carrier rate in Pakistani pediatric population is 2.4% (12). The HBs Ag carrier rate in is 12.24% in unvaccinated thalassemic children (getting multiple blood transfusions) in this study. The vaccination against hepatitis B has reduced this HBs Ag carrier rate to 0.92%. This shows that the vaccination if given in the first year of life is highly effective in reducing HBs Ag carrier rate in thalassemic children.

The studies conducted on thalssemic children vaccinated in the first year of life in Iran (10), Saudi Arabia (13), Greece (14) and India (15) showed excellent protective antibody (anti-HBs) response.

The study done in India showed a high frequency of HBV infection was seen using molecular methods in thalassemic patients (range 8 months to 22 years). The frequency of infection was similar in vaccine responders and non-responders. A number of mutations were observed in the S gene, which could have implications for viral replication as well as virus-host cell interaction (16).

This study included children below five years of age who got maximum of 59 blood transfusions in cases of unvaccinated children and 55 in cases of unvaccinated children, so further studies are needed to know the effect of hepatitis B vaccination in older children and receiving more than this amount of blood.

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