Indian Pediatrics 1999;36:581-583

Immunogenicity of a Low Dose of Indigenously Developed Recombinant Hepatitis B Vaccine in Neonates and Infants

Hepatitis-B remains one of the most important diseases world-wide and accounts for one to two million deaths(1). Universal immunization against Hepatitis-B was started in USA in the year 1991(2). The World Health Organization has recommended the inclusion of Hepatitis-B vaccine in the routine schedule of Universal Immunization Programme in all countries. More than 30 countries have adopted this recommendation(3).

HBV is known to cause acute hepatitis, chronic carrier state, chronic hepatitis, cirrhosis of liver and hepatocellular carcinoma. It is transmitted both vertically (mother to infant) and horizontally from person to person. Carriers are the main reservoir and the chain of transmission can be halted effectively only by the presently available safe vaccines(4). Immunization of only high-risk group will not reduce the reservoir of carriers. Universal immunization will certainly reduce the risk of infection and protect against both vertical and horizontal infection (2-4). HBV infection is a major public health problem in India, as there are 43 million estimated carriers. HBsAg positivity in children below 15 years ranges from 1.3 to 12.7% in Singapore(5).

An important reason why India has not been able to resort to routine immunization has been the prohibitive cost of the vaccine(3,6). The need for a cheaper indigenously manufactured Hepatitis-B vaccine is obvious. This vaccine should also be clinically safe and immunogenic. The present study was designed to evaluate these aspects in the first indigenously developed recombinant Hepatitis-B vaccine (Shanvac-B) in neonates and infants.

Subjects and Methods

Thirty four children belonging to the age group of 3 days to 11 months were evaluated. There were 6 neonates (youngest was 3 days old), 22 children were aged between 1 month to 6 months and 6 children were in the age range of 6 months to 11 months (oldest was 11 months of age). There were 19 boys and 15 girls. All children were administered 5 µg (0.25 ml) of the vaccine intramuscularly in anterolateral thigh region with disposable needles and syringes. The vaccination schedule followed was 0, 1 and 2 months. Each child was seen exactly after 1 month and at each follow up a blood sample of 1 ml was collected. The samples were coded and analyzed in the Gastroenterology Department of Nizam's Institute of Medical Sciences, Hyderabad. Antibody test for HBsAg was done by ELISA (Abbott laboratories). The antibody titers were estimated using a Quantitation panel. Samples giving the titers beyond the range of quantitation panel were diluted and retested. Thirty subjects completed the study and were subsequently analyzed.

Results

In the 30 children who had 90 samples collected and analyzed one month after each dose of the vaccine, the sero conversion rate was 37% after first dose and 100% after second and third doses. The GMT (Geometric Mean Titers) were 26.59 mlU/ml after the first dose, 154.01 mlU/ml after second dose and 1741.63 mlD/ml after third dose. The anti HBs antibody titers ranged from 121.8 mlU/ml to 15,610.6 mlU/ml. The frequency distribution of anti HBs titers is depicted in Table I.

There were no side effects of vaccination such as fever, pain, malaise or rash.

Discussion

The safety and immunogenicity of the tested vaccine was excellent as revealed by 100% sero conversion, high antibody titers and no reported side effects. One quarter of children had very high titers (5000-15000) indicating the likely prolonged duration of the protective efficacy of the vaccine. The other 22 children had anti HBs levels ranging from 121.08 to 2760.75 mlU/ml which represents satisfactory protective level against HBV infection. Earlier studies in infants and neonates using different doses of other recombinant vaccines have reported sero conversion from 98 to 100%. The GMT with 0, 1 and 2 months schedule was 209 mlU/ml while it was much higher (4023 mlU/ml) with 0, 1,6 month schedule(7).

TABLE I - Distribution of Anti-HBs After Third Dose. .

Titer                       Number (%)

10-100                          0 (0)

100-1000                     9 (30)

1000-5000                   13(43)

5000-10000                  5 (17)

> 10000                        3(10) 

 
The duration of effective protective levels of antibodies with the tested vaccine have to be further evaluated after 4-5 years. A four year follow up of 122 children aged 1-12 years given three doses of 0, 1, 6 months schedule of recombinant vaccine, showed that 3 months after the 3rd dose (0.6 to 5 µg/ dose), 93 to 100% had levels of anti HBs 10 mlU/ml, the GMT ranged between 1088 and 1699 mlU/ml, respectively, Four years later the GMT of antibody declined between 73 and 119 mlU/ml and the proportion of children with seroprotection levels declined between 70 to 87%. The degree to which the anti HBs levels declines were directly related to the peak levels achieved(5,8).

It is likely that some loss of circulating levels of anti HBs may occur many years after immunization and an anamnestic response to a booster dose of vaccine usually occurs. Moyes et aI., immunized 78 children with either I or 2 µg of plasma derived vaccine and evaluated them at 4 years of age. A total of 38% and 17% of the children had antibody titers less than 10 mlU/ml, respectively. When a booster dose of recombinant vaccine (2 µg) was given, their antibody titers in- creased 100 fold from preliminary 25 to 2574 mlU/ml in the Iµg primary vaccine group and from 49 to 4786 mlU/ml in the 2 µg vaccine (9). From these and some other studies in Africa and South East Asia(1, 8-10) it can be surmised that the seroprotective levels of anti HBs are likely to last for 5 years or more. However, the immunogenicity of the tested vaccine in the current study will require evaluation after 5 years for confirmatory evidence. Our results indicate that 5 µg dose provides satisfactory seroconversion and will reduce the cost of primary vaccination.

Acknowledgements

We are thankful to M/s Shantha of Biotechnics Private Limited, Hyderabad for supplying the vaccine and other material for this study. We also thank the nursing, technical and secretarial staff of both institutions for the help rendered during conduction of the study.
 

 References

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