Hepatitis A Virus (HAV) is prevalent among children. The epidemic rates of HAV are 38.8% and 54.2% ^[1] at urban and rural areas respectively for the children aged from 1 to 4. Therefore, it is very imperative to apply the safe and effective HA vaccine to the Chinese children so as to decrease the HAV infection. The activated HA vaccine ^[2-3] and inactivated HA vaccine (imported) ^[4] have the good immune response. The domestic inactivated HA vaccine have been proved for its good safety and immunogenicity applied in adults, but there is no report on application for children till now. This study initially observed the safety and the immunogenicity of the domestic inactivated hepatitis A vaccine applied in susceptive children (aged 1-4), as the follows.

1.        Materials and Methods

1.1    Vaccine: The inactivated hepatitis A vaccine provided by Tangshan Yi’an Bioengineering Co., Ltd., containing viral antigen at 500U in each dose, with the ratified number of 971201.

1.2    Vaccinated objects: in the adjacent villages with similar economic level, hygiene conditions and living habits in a mountain area, 63 healthy and susceptive children (anti-HAV, negative HBsAg; normal ALT; normal clinic examinations on heart, lung, liver, and spleen; without allergic history) aged from 1 to 4 were chosen, who were divided into two groups taking the village as the unit at random, with the sex proportion of male and female at 1:1.3, and the average age at 2.3.

1.3    Vaccination method and schedule: injection at the deltoid muscle of the upper arm. The first dose was the primary immunization, and the second dose was vaccinated after 3 or 6 months as the booster immunization (0.3 or 0.6 schedule).

1.4    Side effect observation: all the objects were observed in 30 minutes after the vaccination for the instant reaction, and the local reactions (rubefaction, swell, hot and pain) and the systematic reactions (fever, hypodynamia, headache, dizzy, nausea, inappetence, and rash) were observed after 24, 48 and 72 hours respectively.

1.5    Serological test

1.5.1   Taking venous blood sample: the venous blood sample was taken when the stomach was empty, 3 ml for each time, to asepsis separate the serum, kept at -20℃ for test.

1.5.2   Standard Hepatitis A antibody: it was provided by the WHO as the frozen one, with the ratified number of 990201. 1.0ml distilled water was filled to dilute in each ampoule, with the concentration at 98.6U/ml, kept at -20℃ for after

1.5.3   The positive seroconversion rate of the HAV antibody: Adopted the ELISA agent to test, provided by the Abbott Company, with the ratified number of 5477 RM100, the sensitivity of 23.8-47.5 mU/ml; the competitive restraint method, the competitive restraint rate of the sample > 50% was taken as the positive HAV antibody.

1.5.4   The HA antibody titer test, Made use of the HA antibody testing agent calibrated by the standard HA antibody, with the ratified number of 990528, and the sensitivity of 106-127 mU/ml. Within the proper dilution range, the logarithm of the standard antibody level and the absorbency (A value) were linear regressed, so as to gain the linear regression formula, according to the real dilution of the sample, and the A value measured by the standard antibody, the mU/ml of the antibody could be calculated in the regression formula. A value must be within the linear range of the A value of the standard antibody.

1.5.5   HA IgM antibody test: Adopted the ELISA Seizing Method, and the agent box was provided by Tangshan Yi’an Bioengineering Co., Ltd., with the ratified number of 981103.

1.5.6   HBsAg test: Adopted the ELISA Method, and the agent box was provided by Shanghai Industry Kehua Biological Technology Co., Ltd., with the ratified number of 980605, and 980702.

1.5.7   The Abnormality Liver Test: the Laishi Method was chosen for the ALT test, ≤40U being as normal, produced by Beijing Chemical Plant, with the ratified number of 980820.

2          Results

2.1    The safety of the vaccine: among the 63 personnel who were applied the inactivated hepatitis A vaccine, after the first dose, the instant reaction wasn’t occurred, the local effect was found on 2 persons, accounting for 3.17%, mainly being as rubefaction and swell, with diameter less than 0.5cm; the systematic effect were found on 5 persons, accounting for 7.94%, mainly being as fever but keeping body temperature less than 37.5℃. After the second dose was applied, the local effect was not found, and the systematic effect was found on 4 persons, accounting for 6.35%. The local and systematic effects were found within 8-24 hours, and disappeared within 36 houses, being as the transition reaction; meanwhile, the ALT abnormality hadn’t been found.

2.2    The immune response after the inactivated hepatitis A vaccine was applied

2.2.1   The immune response in 1 month after the primary immunization: after the fist dose was applied for 1 month, the anti-HAV positive seroconversion rate was 85.7% (56/63), and the anti-HAV GMT was 182 mU/ml.

2.2.2   The immune response in 3, 6 months after primary immunization: in 3 months after the primary immunization, the anti-HAV positive seroconversion rate was 88.5% (23/26), and the anti-HAV GMT was 243 mU/ml; in 6 months after the primary immunization, the anti-HAV positive seroconversion rate was 83.8% (31/37) and the GMT was 280 mU/ml. Comparing these two groups, the differences of them were not significant.

               2.2.3  The immune effect in 1 month after the booster immunization: in one (1) month after the booster immunization by 0.3 schedule or 0.6 schedule, the anti-HAV positive seroconversion rate was 100%, GMT was 2718 mU/ml or 4683 mU/ml, and there was no significant difference comparing these two groups. t=2.318, P<0.05, see table 1.

Table 1       Antibody effects of the inactivated hepatitis A vaccine in 1 month after the booster immunization

2.2.4   The anti-HAV dynamics after applied the inactivated hepatitis A vaccine: the positive seroconversion rates of the anti-HAV antibody in 1, 3 and 6 months after the primary immunization and in 1 month after the booster immunization were 85.7%, 88.5%, 83.8%, and 100.0% respectively, while the GMTs were 182 mU/ml, 243 mU/ml, 260 mU/ml and 4683 mU/ml respectively as well.

3          Discussion

According to the national epidemic investigations, it shows that the annual HAV infection rate under 4 years old is obviously higher than those at other phases ^[1]. Therefore, the optimal objects of the HAV prevention should be the children at low ages. After the domestic inactive hepatitis A was vaccinated, the local and systematic effects were all in transition. The local effect rate (3.17%) of the inactivated hepatitis A vaccine on the children at low ages was lower than that on the children at high ages (5.8%) ^[6], but higher than that of the Baweixin hepatitis A vaccine (1.9%) ^[7]. And the systematic effect rate (7.9%) was equivalent to the document ^[6] (6.4%), but higher than ^[7] (1.9%). Since this study didn’t set up the blank comparison group, the side effect caused by the non-characteristics factors couldn’t be eliminated. The ALT was not found after the vaccination, which showed that the domestic inactivated hepatitis A was safe. The anti-HAV positive seroconversion rates in 1, 3 and 6 months after primary immunization were 85.7%, 88.5% and 83.8%. The GMTs of antibody were 182 mU/ml, 243 mU/ml, and 260 mU/ml, which showed that the susceptive children could gain the good protective antibody after one dose of 500U inactivated hepatitis A vaccine was applied, and this vaccine had the good immunogenicity.

In 1 month after the booster immunization, the anti-HAV positive seroconversion rates of the 0.3 month schedule and 0.6 month schedule were 100.0%, and the antibody GMTs were 2718 mU/ml and 4638 mU/ml, which indicated that these two schedules could gain the good antibody responses at high levels. Compared with these two schedules, the statistical difference was found to show the 0.6 month schedule was superior to 0.3 month schedule, being consistent with the result of the children at high ages (aged 5-15) ^[6].

In general, the domestic inactivated hepatitis A vaccine has the good safety and immunogencity applied in the children at low ages; the high-titer hepatitis A antibody can be gained after two doses of HA vaccine are applied; the 0.6 schedule is superior to 0.3 schedule.

Thanks to Cui Lianyun, Liu Zhonglin and Lihaijun for their participation.

References:

^[1]      Dai Zhicheng, Qi Guoming, Investigation on Viral Hepatitis Seroepidemiology in China (Ver. 1), Beijing: Science and Technology Works Press, 1997, 21

^[2]    Yang Minji, Zhu Xiaozhong, Ge Chengfu, and Associates, Observations on the Serum Antibody and Effects after the Primary Students were Applied with the Activated Hepatitis A Vaccine, Chinese Journal of Preventive Medicine, 1990, 24 (5): 306.

^[3]      Zhang Shuya, Mao Jiangsen, Huang Haiying, and Associates, Investigation on the Safety of the Activated HAV Vaccine Applied on Human, China Medicine Magazine, 1990, 70 (12): 682.

^[4]      Innis B. Snihbhan R. Kunasol P, et al. Protection against hepatitis A by an inactivated vaccine JAMA 1994 271:1328

^[5]      Ren Aiguo, Ma Junrong, Feng Fumin, and Associates, Study on Safety and Immnogenicity of the Domestic Inactivated Hepatitis A Vaccine, China Journal of Experimental and Clinical virology, 2001, 15 (4): 71.

^[6]      Liu Chongbo, Ren Yinhai, Zhang Yucheng and Associates, Study on Safety and Immunogenicity and Vaccination Schedule of the Domestic Hepatitis A Vaccine Applied on Children, China Planning Immunology, 2002, 8 (1): 1-3

^[7]      Huang Guibiao, Wan Zongju, Li Rongcheng, Study on Safety and Immunogenicity of the Baiweixin Inactivated Hepatitis A Vaccine Applied on Children and Adults, Chinese Journal of Epidemiology , 2000, 21 (4): 287.