Elsevier ELSEVIER zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Single-dose comparison adolescents Vaccine, Vol. 14, No. 12, pp. 1092-1094, 1996 Copyright 0 1996 Elsevier Science Ltd. All rights reserved Printed in Great Britain PII: S026440X(96)00053-9 0264-410X/96 $15+0.00 hepatitis A vaccination: of different dose levels in Yong Poovorawan*$, Apiradee Theamboonlers” and Assad Safaryy zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPO The eflect of two dose levels of inactivated hepatitis A vaccine was investigated for irnmunogenicity and reactogenicity in an open study in adolescents. The subjects were randomised into two groups and to receive a priming dose of 720 EL. U or 1440 EL. U of hepatitis A antigen, respectively. A booster of the same dose level was given at month 6. In group I, receiving 720 EL. U, the seroconversion rates at 15 days and I month were 92’% and 99% The corresponding rates for group 2, receiving 1440 EL. U, were 98’%and ZOO’%. Higher geometric mean titres of antibody to hepatitis A virus were noted at I, 6 and 7 months in the group receiving 1440 EL. U. The vaccine was well tolerated in both groups, The most frequent side effect was transient soreness at the site of inoculation. No serious adverse reactions were observed. The study demonstrated that inactivated hepatitis A vaccine is safe and immunogenic at a dose level af 720 EL. U or 1440 EL. U in adolescents. Copyright 0 1996 Elsevier Science Ltd. Keywords: Hepatitis A; adolescents; two dose levels Serological surveys have shown that the prevalence of hepatitis A in a region is closely related to the level of economic development. In countries with a poorly developed infrastructure many children become infected within the first years of life; indeed, 50% are seropositive by the age of 5 years’. As standards of hygiene improve, an increasing proportion of the infections are delayed until early adult life. Characteristically, plots of the age specific prevalence of the antibody to hepatitis A virus (anti-HAV) follow a sigmoidal pattern2 as the incidence of disease is displaced towards these older groups. Infections in early childhood are usually mild and may be clinically apparent, while symptomatic infections with hepatitis A are more likely to occur with increasing age3. As living conditions improve, this may lead, para- doxically, to an increase in disease burden, reflecting the fact that those infections that do occur are at an age when they will cause overt disease. In addition, a growth in the number of susceptible individuals may build to a level necessary to sustain an epidemic. Such an instance was recorded in the 1988 Shanghai epidemic when 310476 cases were reported in young adults (average age 28 years) following the consumption of contaminated clams4. In Thailand, a country with a rapidly developing economy. a marked decline in the incidence of hepatitis A amongst the young has been recorded. In school-aged children in Bangkok, a marked reduction in anti-HAV *Chulalongkorn University, Bangkok, Thailand. tSmithKline Beecham Biologicals, Rixensart, Belgium. $To whom corre- spondence should be addressed. (Received 11 October 1995; revised 5 February 1996; accepted 27 February 1996) 1092 Vaccine 1996 Volume 14 Number 12 prevalence was noted over a 16 year period5,6. These studies depict the changing epidemiological status in children and adolescents, where it is apparent that increasing numbers are at risk from HAV and would thus benefit from vaccination against this disease. This paper reports on the immunogenicity and safety of SmithKline Beecham Biologicals hepatitis A vaccine in a susceptible adolescent population. MATERIALS AND METHODS Two hundred and two adolescents (aged 12-19 years) with anti-HAV IgG negative from the “Wat Sangvej” school in Bangkok were enrolled into this open study. They were randomized into two groups and immunized with SmithKline Beecham Biologicals inactivated hepatitis A vaccine (Havrix@). Group 1 received 720 EL.U of antigen in a dose of 0.5 ml and Group 2, 1440 EL.U in 1 ml. The antigens were adsorbed onto aluminium hydroxide (0.5 mg ml-‘). A booster of the same dose level was administered at month 6. Blood samples were obtained 5 days prior to vaccina- tion for determination of anti-HAV antibodies and for liver enzyme activities (alanine aminotransferase and aspartate aminotransferase). After vaccination, samples were taken at day 15, and months 1, 6 and 7 for the titration of anti-HAV antibodies. On the day of vaccination, and for three subsequent days, local symptoms (soreness, redness, swelling) and general symptoms (fever, temperature, headache, malaise, loss of appetite, nausea, vomiting) were recorded.