More than 2 billion people in the world are infected

CLINICAL GASTROENTEROLOGY AND HEPATOLOGY 2004;2:941 945 18-Year Follow-up Study of a Prospective Randomized Trial of Hepatitis B Vaccinations Without Booster Doses in Children MAN FUNG YUEN,* WEI LING LIM, ANNIE ON ON CHAN,* DANNY KA HO WONG,* SIMON SIU MAN SUM,* and CHING LUNG LAI* *Department of Medicine, Queen Mary Hospital, University of Hong Kong, Hong Kong; and Department of Health, Hong Kong, China Background & Aims: The long-term immunogenicity and efficacy of hepatitis B virus (HBV) vaccination remain to be defined. We aimed to examine the long-term immunogenicity and efficacy of HBV vaccination with 3 different regimens over 18 years of follow-up. Methods: A total of 318 Chinese subjects receiving 3 different regimens of HBV vaccination (2-dose recombinant vs. 3-dose recombinant vs. 3-dose plasma-derived vaccines) without receiving a booster dose were recruited. The HBV serologic markers, including hepatitis B surface antigen (HBsAg), antibody to hepatitis B surface antigen (anti-hbs), and antibody to hepatitis B core antigen (anti- HBc), were determined at yearly follow-up. After 18 years, 88 subjects were still being followed up. Results: Compared with subjects receiving the 2-dose regimen, subjects receiving the 3-dose regimens had a significantly higher geometric mean titer of anti-hbs and a higher proportion had anti-hbs titers >10 miu/ml during the 18 years of follow-up. There were no differences in these 2 parameters between subjects receiving the 3-dose recombinant and subjects receiving the 3-dose plasma-derived vaccines. A total of 88 anamnestic responses were documented in 70 subjects (8 with initial anti-hbs titers <100 miu/ml at 12 months and 7 with anti-hbs titers <10 miu/ml before the anamnestic responses). No subject became positive for HBsAg. Three subjects had benign breakthrough HBV infection without leading to chronicity indicated by isolated anti-hbc positivity. Conclusions: There was less long-term immunogenicity associated with the 2-dose regimen when compared with the 3-dose regimens of HBV vaccination. Because of the highly effective anamnestic responses, a booster dose was not necessary at least up to 18 years after the primary vaccination. More than 2 billion people in the world are infected with hepatitis B virus (HBV). Of these, about 400 million are chronic hepatitis B carriers. 1,2 It is estimated that there will be more than 50 million new HBV infections every year if there are no effective vaccination programs. 3 Universal vaccination is the most effective method to control HBV infection worldwide. A national HBV vaccination program has also been shown to effectively reduce the occurrence of hepatocellular carcinoma in Taiwan. 4 To date, universal vaccination programs have been implemented in about 154 countries around the world. 5 The most important issue concerning HBV vaccination is its long-term efficacy in preventing HBV infection. Whether booster doses of vaccine are necessary to maintain long-term immunity is still under debate. Most follow-up studies suggest that booster doses are probably not necessary in immunocompetent subjects because of the effective secondary (anamnestic) responses generated from memory B cells, 6 16 with the longest follow-up study from Taiwan reporting a 14-year period of follow-up after the primary vaccination. 8 According to the recommendations from the European Consensus Group on Hepatitis B Immunity in 2000, 9 continuous longterm monitoring is required to determine whether an HBV carrier state develops after 15 years of primary vaccination. We have previously reported a 5-year and a 12-year long-term follow-up study on the efficacy of recombinant and plasma-derived vaccines without booster doses in children. 6,7 The aim of the present extended study was to examine the long-term immunogenicity and efficacy of HBV vaccination at 18 years of follow-up. Subjects and Methods Subjects Close relatives of HBV carriers were recruited into the trial between November 1984 and February 1986. The subjects were between 3 months and 11 years of age. They were screened for hepatitis B surface antigen (HBsAg), antibody to hepatitis B surface antigen (anti-hbs), and antibody to hepatitis B core antigen (anti-hbc) by radioimmunoassays (AUS- Abbreviations used in this paper: anti-hbc, antibody to hepatitis B core antigen; anti-hbs, antibody to hepatitis B surface antigen; GMT, geometric mean titer; HBV, hepatitis B virus; HBsAg, hepatitis B surface antigen. 2004 by the American Gastroenterological Association 1542-3565/04/$30.00 PII: 10.1053/S1542-3565(04)00384-2

942 YUEN ET AL. CLINICAL GASTROENTEROLOGY AND HEPATOLOGY Vol. 2, No. 10 RIA II, AUSAB, and COBAS, respectively; Abbott Laboratories, North Chicago, IL). Inclusion criteria were as follows: (1) serum negative for HBsAg, anti-hbs, and anti-hbc; (2) serum alanine aminotransferase level 50 U/L; (3) no history of receiving hepatitis B immunoglobulin within 4 months of recruitment; and (4) no history of serious systemic illnesses or allergy. Patients or guardians were given full explanations of the study before written consent was obtained. Vaccination Protocol Children were randomized into 3 groups receiving different regimens of vaccination. Randomization was performed by computer-generated assignment. Children in group 1 received two 5- g doses of recombinant DNA yeast vaccine (H-B-VAX II; Merck Sharp & Dohme, West Point, PA) at 0 and 1 months; children in group 2 received three 5- g doses of H-B-VAX II at 0, 1, and 6 months; and children in group 3 received three 10- g doses of plasma-derived vaccine (H-B-VAX) at 0, 1, and 6 months. Children who did not develop anti-hbs and those with an anti-hbs titer of 10 miu/ml at 8 months were given a booster dose at 12 17 months. These subjects were excluded from the analyses. No booster dose was given to any other subject during follow-up. Subject Monitoring All of the subjects had a scheduled follow-up at yearly intervals until the time of this report. Subjects who did not attend the follow-up were recalled to attend the follow-up in the subsequent year. Sera were taken at every follow-up for determination of HBsAg, anti-hbs, and anti-hbc titers. Subjects were considered to have HBV infection if at least 2 consecutive sera were positive for anti-hbc, HBsAg, or both. Anamnestic Response Because the anti-hbs titers of all the vaccinated subjects decreased within 12 months of the first dose of vaccination, a significant increase in the anti-hbs titers in subjects not receiving booster doses at the subsequent follow-up implies a generation of secondary (anamnestic) response after exposure to HBV. Using the criteria defined in our previous reports, 6,7 an anamnestic response was defined by the following criteria. (1) For subjects with anti-hbs titers that decreased after 12 months to an undetectable level or levels 10 miu/ ml, the increase in the anti-hbs titers should be 100 miu/ml. (2) For subjects with anti-hbs titers 10 miu/ml, the increase in the anti-hbs titers should be more than 2 times the previous values with the absolute levels of 200 miu/ml. Statistical Analysis The statistical analyses were performed with the 2-tailed Student t test for the continuous variables, 2 test, and Fisher exact test for categorical variables. Correlation between variables was performed by a correlation test with the Pearson coefficient. The skewed anti-hbs titers were transformed into logarithmic values for statistical analyses. Results Demographics A total of 318 subjects were randomized into the 3 groups. The number, sex, and mean age of these subjects in each group at study entry are listed in Table 1. Eleven subjects (6 in group 1, 2 in group 2, and 3 in group 3) had an anti-hbs titer 10 miu/ml at 8 months and were given a booster dose at 12 17 months. These subjects were excluded from the subsequent analyses. There were no differences among the 3 groups in the percentages of patients who did not have anti-hbs titers 10 miu/ml at 8 months (P NS for all). After 18 years, 88 of these subjects were still being followed up. Geometric Mean Titer The geometric mean titer (GMT) and the proportions of subjects with an anti-hbs titer 10 miu/ml in different groups at the first, fifth, 10th, and 15th years of follow-up are listed in Table 2. The anti-hbs titer at 12 months correlated positively with the anti-hbs titers in all of the subsequent follow-ups in the whole study population (r values ranging from 0.67 to 0.88; P 0.001 for all). As reported in our previous study, subjects in groups 2 and 3 had a significantly higher GMT than subjects in group 1 in the first 12 years of follow-up. 7 In the present study, subjects in group 2 continued to have a significantly higher GMT compared with subjects in group 1 throughout the subsequent follow-up to 18 years. Subjects in group 3 also had a significantly higher GMT compared with subjects in group 1 at the 17th year of follow-up (a trend toward significance at the 16th year Table 1. Demographic Data of the 318 Patients in the Study Group 1 Group 2 Group 3 No. of patients 105 106 107 Male/female 48/57 52/54 48/59 Mean age, yr (range) 5.4 (0.9 11.25) 5.6 (0.3 11.75) 5.3 (0.25 11.9) NOTE. The male-to-female ratio at the 18th year of follow-up was 39/49 (group 1, 11/14; group 2, 15/15; group 3, 13/20). There were no significant differences in the sex ratios in each respective group at baseline and at the last follow-up.

October 2004 LONG TERM FOLLOW UP OF HBV VACCINATION 943 Table 2. Immunogenicity of the 3 Groups of Subjects During Follow-up Follow-up (yr) 1 5 10 15 16 17 18 Group 1 No. of subjects 99 72 52 35 36 28 25 titer 10 miu/ml (%) 88 (88.8) a,b 54 (75) 37 (71.2) c 19 (54.3) 19 (52.8) d 14 (50) e,f 12 (48) g GMT (miu/ml) 83 h 47 h 36.0 i,j 24.9 k 11.0 l,m 8.8 n,o 10.0 p Group 2 No. of subjects 99 63 55 37 37 34 30 titer 10 miu/ml (%) 97 (98) a 55 (87.3) 45 (81.8) 27 (73.0) 30 (81.1) d 26 (76.5) e 22 (73.3) g GMT (miu/ml) 1085 h 131 h 80.5 i 47.5 k 63.6 l 50.1 n 35.3 p Group 3 No. of subjects 104 64 56 36 44 45 33 titer 10 miu/ml (%) 101 (97.1) b 54 (84.3) 51 (91.1) c 23 (63.9) 32 (72.7) 33 (73.3) f 19 (57.6) GMT (miu/ml) 858 h 250 h 89.1 j 24.5 26.9 m 29.0 o 20.3 a P 0.018; b P 0.026; c P 0.012; d P 0.01; e P 0.03; f P 0.043; g P 0.05; h P 0.001; i P 0.005; j P 0.028; k P 0.009; l P 0.002; m P 0.07; n P 0.005; o P 0.02; p P 0.049. of follow-up; P 0.07). There were no differences in the GMT between subjects in group 2 and subjects in group 3 throughout the 18 years of follow-up. Protective Anti-HBs Titer Groups 2 and 3 had higher proportions of subjects with anti-hbs titers 10 miu/ml (defined as the protective titer) 17 compared with group 1 throughout the follow-up period (Table 2). These differences in the proportions of subjects with protective anti-hbs titers were statistically significantatthe first, 16th, 17th, and 18th years of follow-up when group 2 was compared with group 1 and at the first, 10th, and 17th years of follow-up when group 3 was compared with group 1 (Table 2). There were no differences in the proportions of subjects with protective anti-hbs titers between group 2 and group 3 throughout the 18 years of follow-up. Anamnestic Response During the 18 years of follow-up, 70 patients had at least one anamnestic response (26 in group 1, 23 in group 2, and 21 in group 3). There were a total of 88 episodes of anamnestic responses in these 70 patients. Fifty-six subjects had only one episode of anamnestic response; 11 subjects, 2 subjects, and one subject had 2, 3, and 4 episodes, respectively. The exact increase in anti-hbs titers of all the anamnestic responses are shown in Figure 1. Among these 70 subjects, 8 subjects (all in group 1) (11.4%) had anti-hbs titers 100 miu/ml at 12 months. In addition, 7 episodes of the anamnestic responses were in subjects with the preceding anti-hbs titers of 10 miu/ml (3 with undetectable anti-hbs levels and 4 with anti-hbs levels ranging from 1 to 9 miu/ml) (Figure 1). HBV Infection Thirty-four of 88 patients (38.6%) had anti- HBs titers 10 miu/ml at the last follow-up. However, no subject became positive for HBsAg. Three subjects became weakly positive for anti-hbc. One subject in group 2 became positive for anti-hbc with Figure 1. The anamnestic responses of (A) 63 subjects with anti-hbs titers 10 miu/ml and (B) 7 subjects with anti-hbs titers 10 miu/ml.

944 YUEN ET AL. CLINICAL GASTROENTEROLOGY AND HEPATOLOGY Vol. 2, No. 10 an anti-hbs titer of 36 miu/ml at the ninth year of follow-up (at the age of 12.0 years). He was persistently positive for anti-hbc throughout the subsequent follow-up. The second subject (in group 1) became positive for anti-hbc with an anti-hbs titer of 22 miu/ml at the 11th year of follow-up (at the age of 15.3 years). The third subject (in group 3) became positive for anti-hbc with an anti-hbs titer of 76 miu/ml at the 17th year of follow-up (at the age of 18.3 years). The latter 2 subjects did not attend follow-up afterward, and their subsequent anti-hbc status could not be determined. Discussion According to our previous report with 12 years of follow-up, there are no differences in the long-term immunogenicity (as measured by the GMT and the proportion of subjects with an anti-hbs titer 10 miu/ml) and efficacy of HBV vaccination between the 3-dose regimens of recombinant vaccine (group 2) and plasma-derived vaccine (group 3). 7 Although the long-term immunogenicity for subjects receiving 2 doses of recombinant vaccine (group 1) was lower when compared with those in groups 2 and 3, there were no differences in the protective efficacy between the 3 groups. The present study extended the follow-up to 18 years. To our knowledge, this is the longest follow-up study on the immunogenicity and protective efficacy of the HBV vaccines. Although only 88 patients attended the last follow-up at the 18th year, the results of the present study were unlikely to be biased because all of the subjects were family members of patients with chronic hepatitis B and the 2 major reasons for not attending follow-up were emigration from Hong Kong and inability to attend follow-up because of daytime working duties. In addition, there were no differences in the sex ratios of each group at baseline and at the last follow-up (Table 1). Similar to our previous report at 12 years of follow-up, 7 3-dose regimens are preferable to 2-dose regimens to achieve better long-term immunogenicity (Table 2), although the extra cost for one more dose of vaccine may be an important consideration for developing countries. Anti-HBs titers wane with time after the primary vaccination. The present study showed that the anti-hbs titers at 12 months after primary vaccination correlated positively with the anti-hbs titers at each year of subsequent followup. This finding is in accordance with the study by Theppisai et al. 18 The higher the anti-hbs titers achieved after the primary vaccination, the better the long-term immunogenicity. A more important issue is whether immunogenicity can be effectively restored in subjects with anti-hbs titers lower than the arbitrarily defined protective level (anti-hbs titer 10 miu/ml) without a booster dose. In the present study, anamnestic responses were observed in 70 subjects with a total of 88 episodes (Figure 1). There were 2 important issues concerning these anamnestic responses. Firstly, 8 subjects with anamnestic responses had anti-hbs titers 100 miu/ml at 12 months after the primary vaccination. Secondly, 7 episodes of anamnestic responses were from subjects with anti-hbs titers 10 miu/ml. Therefore, anamnestic responses could be of significant magnitude even when the initial anti-hbs titers at 12 months were not particularly high and, more importantly, even when the subsequent anti-hbs titers had decreased to 10 miu/ml. The anamnestic responses observed in our Chinese subjects may be partly related to the fact that they had a higher risk and frequency of contracting HBV from their HBsAgpositive family members. However, we believe that our results are applicable to subjects in western countries where the general incidence of HBV infection is low. It has been shown that remarkable immune responses can be obtained in vaccinated western populations with unprotective anti- HBs titers when subjects are given purified nonadsorbed HBsAg. 19 The reason may be that the number of memory B cells does not decrease with time despite the decline of the antibody level. 20 Braito et al. also showed that in western populations, decline of anti-hbs level does not necessarily mean a loss of immunity. 21 According to various studies, anamnestic responses can be generated within 3 5 days of exposure of HBV, 19,22,23 although it has also been suggested that the 3- to 5-day period of delay may provide an opportunity for infection to occur. In the present study, no subject tested positive for HBsAg. Only 3 subjects became weakly positive for anti-hbc. This indicated transient benign breakthrough infections without resulting in the chronic carrier state. According to a Taiwan study with 14 years of follow-up, only 2 of 258 vaccinated children who had not received a booster dose became positive for anti- HBc without HBsAg positivity. 24 The low infective rate of HBV in the present study is of particular importance for 2 reasons. Firstly, the study subjects were at a higher risk of contracting HBV because they were all close relatives of HBV carriers. Secondly, 35 subjects (39.8%) had anti-hbs titers 10 miu/ml at the last follow-up (Table 2). HBV vaccination even without a booster dose is effective in prevention of HBV infection for at least up to 18 years. In conclusion, in subjects who had developed an adequate anti-hbs response (i.e., 10 miu/ml) after the primary vaccination, a booster dose was not necessary to prevent HBV infection at least up to 18 years because of the highly effective anamnestic responses despite the decline in anti-

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