Comparison of the Immune Response of Four Different Dosages of a Yeast-Recombinant Hepatitis B Vaccine in Singapore Children: A Four-Year Follow-Up Study

Article excerpt

Introduction

The scarcity of suitable plasma for the manufacture of hepatitis B vaccine and the possible transmission of human immunodeficiency virus [1] led to the development of genetic-engineered vaccines. One of the recombinant DNA hepatitis B vaccines is produced in yeast (Saccharomyces cerevisiae) that has been inactivated by formalin, absorbed in aluminium hydroxide and purified by hydrophobic chromatography [2]. The safety and immunogenicity of the yeast-derived vaccines in children and adults have been demonstrated [3-5]. The vaccine is well tolerated, with side-effects similar to those of plasma-based vaccine [4]. There was no increase in antibody titre to Candida albicans [3] or elevations of IgE-specific antibodies to S. cerevisiae [6] among the vaccinees. The vaccine is a efficacious as the plasma-based vaccine in the prevention of perinatal transmission of hepatitis B virus (HBV) infection [7].

Owing to the high cost of the DNA-recombinant yeast-derived vaccine (as high as the plasma-based vaccine when it was first marketed), clinical trials were conducted in Singapore to evaluate the immunogenicity and efficacy of reduced dosages of the recombinant vaccine in infants, children, teenagers [8] and adults [9]. If a lower dosage is compatible with both immunogenicity and efficacy, the cost of the vaccination programme could be reduced considerably. This is of particular importance in developing countries where HBV infections is endemic. We report the findings of our study on the immune response of healthy children to four different dosages of the vaccine, with follow-up for 4 years.

Materials and methods

The study population were 1-12-year-olds who were on regular follow-up in a postnatal clinic at Kandang Kerbau Hospital. The purpose of the trial was carefully explained to the parent or guardian and informed consent was obtained before venous blood (5 ml) was collected from each child using disposable needles and syringes. At the time of blood collection, relevant demographic data such as date of birth, weight, height, sex and ethnic group of each child were recorded.

At the end of each collection, the samples were immediately dispatched to the Ransome Research Laboratory, Department of Clinical Research, Singapore General Hospital, where the sera were separated and stored at -70 [degrees] C before analysis in batches. Hepatitis B surface antigen (HBsAg) and antibody to hepatitis B surface antigen (anti-HBs) were tested by radio-immunoassay (AUSRIA II and AUSAB, respectively, Abbott Laboratories, Chicago) and antibody to hepatitis B core antigen (anti-HBc) by enzyme immunoassay (CORZYME, Abbott Laboratories, Chicago). Serum alanine aminotransferase (ALT) was determined by the Greiner Analyser G-400 (Greiner Electronics Diagnostica, Switzerland).

Children found to be negative for HBsAg, anti-HBs and anti-HBc, with normal ALT levels (9-36 IU/ml) and with no previous history of hepatitis B vaccination were randomized into 4 groups (about 30 in each group) to receive 3 doses of 0.6 [Mu] g, 1.25 [Mu] g, 2.5 [Mu] g or 5.0 [Mu] g of Merck, Sharp and Dohme yeast-derived hepatitis B vaccine. The vaccine was mixed well and the given intramuscularly into the upper deltoid muscle using a 0.5 ml insulin syringe type U100 at 0, 1 month and 6 months (0-1-6 schedule). Prior to the administration of the vaccine, the parent or guardian was questioned regarding allergies and children with known allergies to yeast were excluded. The parent or guardian was asked to record any local or systemic complaints which occurred after each vaccination. Blood samples were obtained at 3 months, 6 months (before the last dose was given), 9 months, 12 months, 24 months and 48 months after the first dose, and tested for HBsAg, anti-HBs, anti-HBc and ALT levels. The reciprocal anti-HBs titres were expressed in milli-international units (mIU/ml, based on a WHO Reference Standard supplied by the International Laboratory for Biological Standards, Central Laboratory of the Netherlands Red Cross Blood Transfusion Service). …