Persistence of vaccine-induced antibody to hepatitis A virus G . W i e d e r m a n n *.~, F. A m b r o s c h * , A. S a l a r y *
F. E. A n d r e * , E. D ' H o n d t * , A. D e l e m t a n d
A level o f 10 m l U hepatitis A antibodies/ml as measured by E L I S A is believed to be the minimal protective concentration. I f this level is considered, the mean persistence o f vaccine induced antibodies is approximately 10-11 years after booster dose, 6 - 7 years if only the primary doses are given and 5 - 6 years if the minimal individual titre is taken into account. Keywords: Hepatitis A vaccine; antibody persistence; duration of protection: immunity
INTRODUCTION A study of the persistence of vaccine-induced antibodies to hepatitis A virus (HAV) was performed including calculation of the geometric mean titre after vaccination together with the range of titres, estimation of the disappearance rate of antibodies, and estimation of a minimal protective titre. MATERIALS AND METHODS Inactivated hepatitis A vaccines were prepared from HAV strains CLF and H M i 7 5 , grown on MRC-5 cells, purified, inactivated and adsorbed onto AI(OH)3 as described ~. In a first study group, 110 HAV-seronegative persons were each injected four times, with one of three different doses of the CLF-strain [180, 360 and 720 ELISA units (El.U) at months 0, 1, 2 and 12]. Blood samples were drawn before, and 1 month after, each vaccine dose and at months 6, 12 and 18. In a second study, 69 HAV-seronegative persons received only the 720 EI.U dose (HM175) at months i and 12. Serum samples were drawn before and 1 month after vaccination and at months 6 and 12. The immune response was expressed as percentage seroconversion ( > 20 mIU/ml) and as the geometric mean titre (GMT) of ELISA (mIU/ ml) as described-'. Antibody titres were followed over a period of 12-18 months. For comparison, 23 seronegative persons were passively immunized with standard doses (0.016-0.022 ml/kg) of hepatitis immune globulin (100 IU anti-HAV/ml). Blood samples were drawn 3-5 days later. RESULTS
Immunogenicity and GMTs lmmunogenicity was evaluated with regard to seroconversion and GMT. In the first study three doses of *Institute for Specific Prophylaxis and Tropical Medicine, Kinderspitalgasse 15, Vienna 1095, Austria. *SmithKline Biologicals, Rixensart, Belgium. §To whom correspondence should be addressed 0264-410X/92/100S129-03 (~ 1992Butterworth-HeinemannLtd
vaccine containing the CLF strain were injected following a schedule of vaccination at 0, 1, 2 and 12 months (Table 1). After one injection, a seroconversion rate of ,90% was reached with the two highest doses. After the booster dose at month 12, the G M T was 6578 with the highest dose. Following a schedule of vaccination at 0, 1 and 12 months in the second study with the highest dose of vaccine containing strain HM 175, initial G M T values were lower than in the first study, but after the booster at month 12 there was no statistically significant difference in GMTs between the first and second study (Table 2).
Antibody kinetics The GMTs of blood samples of vaccinees were followed over a period of 18 months in the first, and 12 months in the second, study and the results are shown in Figures 1 and 2. The curves of G M T are roughly parallel indicating disappearance rates independent of antigen dose, vaccine strain and vaccination schedule. From the antibody decrease between months 6 and 12 and 12 and 18 of the first study, the annual decrease rates were calculated. The mean annual disappearance rates in the two periods were 42.5 and 44.3%.
Estimation of minimal protective titre Experience with passive immunization against hepatitis A in > 100 000 travellers 3 has shown that protection could be achieved for at least 3 weeks after administration of 0.015 ml/kg body weight of a hyperimmune globulin (100 IU/ml). This is in accordance with recommendations by the Centers for Disease Control (USA) for 0.02ml immune globulin to be given per kilogram body weight if travel is for < 2 months 4. When this dose was injected into 23 persons with no antibodies against hepatitis A, a mean titre of 21 mIU/ml resulted after 4 days. Since the half-life of passively applied human immune globulins is ~ 21 days, a titre of 10 mIU/ml can be expected after 3 weeks at the end of the protection period 3 and could be considered as a minimal protective concentration. Considering the G M T after immunization with a dose
Vaccine, Vol. 10, Suppl. 1, 1992
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Persistence of vaccine-induced anti-HA t~" G. Wiedermann et al. Table 1
Immunogenicity of hepatitis A vaccine (study group 1, strain CLF) Month 1
Month 2
Month 3
Month 6
Month 12
Month 13
Vaccine dose (El.U)
n
SC(%)
GMT
n
SC(%)
GMT
n
SC(%)
GMT
n
SC(%)
GMT
n
SC(%)
GMT
n
SC(%)
GMT
180 360 720
44 50 8
50.0 94.0 87.5
114 293 713
44 50 8
95.5 98.0 87.5
189 387 890
45 50 8
97.8 100 100
478 793 1365
48 49 8
97.8 100 100
317 530 813
45 47 7
97.8 97.9 100
213 429 637
48 47 7
100 100 100
2143 3808 6578
n, Number of persons; SC, seroconverion; GMT, geometric mean titre 2
Table
Immunogenicity of hepatitis A vaccine (study group 2, strain HM175) Month 1
Month 2
Month 6
Month 12
Month 13
Vaccine dose (El.U)
n
SC(%)
GMT
n
SC(%)
GMT
n
SC(%)
GMT
n
SC(%)
GMT
n
SC(%) GMT
720
66
97
278.1
65
98.5
527.6
57
98.2
483.9
65
98.5
268.9
59
100
5059.4
n, Number of persons; SC, seroconversion; GMT, geometric mean titre
I0 000
3 Persistence of anti-HAV after immunization with hepatitis A vaccine (720 El.U) taking into account different decrease rates
Table
E
-~
iooo
L?
Annual decrease (%)
Time to reach the minimal protective level, (years)
50 45 40
9.4 10.9 12.7
aMinimal protective level of 10 mlU/ml 100 I
I
I
I
I
2
3
6
l
I
I
12 13
Time from f i r s t vaccination
18
Although studies of protection achieved in humans have just become available, an inactivated hepatitis A vaccine has already been shown to be protective in chimpanzees 5.
(months)
1 Time course of anti-HAV titres after immunization with three different doses of an inactivated HAV vaccine. Vaccination at 0, 1, 2 and 12 months. 0 , 1 8 0 El.U; I I , 360 El.U; ©, 720 EI.U Figure
10 000 ~
~
O
E I000
F.L3 100 I
I
I
I
I
2
3
6
I
I
12 13
Time from f i r s t vaccination
I
(months)
2 Time course of anti-HAV titres after immunization with doses of 720 EU inactivated hepatitis A vaccine using two different vaccination schedules. Q, Doses at 0, t and 12 months; & , doses at 0, 1, 2 and 12 months
of 720 EI.U and the annual decrease rate as given above, the mean persistence of vaccine-induced antibodies to reach a borderline concentration of 10 m I U anti-HAV /ml would be 10-ll years after the booster, 6-7 years without a booster and 5-6 years if the minimal individual titre is taken into account (Table 3).
Vaccine, Vol. 10, Suppl. 1, 1992
The persistence of vaccine-induced antibodies is believed to be related to the duration of protection. The importance of humoral immunity is emphasized by the experience with passive immunization 3.4. In addition, Vallbracht 7 and Kurane 6 believe that T cells and natural killer cells also play a role in protection. Finally, it can be hypothesized that after primary vaccination and after the disappearance of antibodies, a subsequent infection could induce a booster effect on antibody levels in due time. Krugman and Hilleman (personal communication) have speculated on this and, although it is disputed for hepatitis B, such a hypothesis could also be relevant for hepatitis A. Controlled trials or observations giving information on the duration of immunological memory are needed.
18
Figure
$130
DISCUSSION
ACKNOWLEDGEMENTS These trials were performed in accordance with the provisions of the Declaration of Helsinki. The trial was approved by the ethical commission of the University of Vienna. Written informed consent was obtained from all volunteers before vaccination. REFERENCES 1 2
Andre, F.E., Hepburn, A. and D'Hondt, E. Inactivated candidate vaccines for hepatitis A. Prog. Med. Virol. 1990, 37, 72-95 Wiedermann, G., Ambrosch, F., Kollaritsch, H., Hofmann, H., Kunz, Ch., D'Hondt, E, Delem, A., Andr6, F.E., Safary, A. and Stephenne, J. Safety and immunogenicity of an inactivated hepatitis A candidate vaccine in healthy adult volunteers. Vaccine 1990, 8, 581-584
Persistence of vaccine-induced anti-HA V: G. Wiedermann et al, 3 Ambrosch, F. and Stemberger, H. Impfungen bei Fernreisen Aktueller Stand. Osterr. Arztezcitung 1983, 39, 715-724 4 Center for Disease Control. Recommendations for Protection against Viral Hepatitis. Morbid. Mortal Week. Rep. 1985, 34, 313-335 5 Andre, F.E. and Hepburn, A. Current Status of HA V Vaccine Development Working Group on the Control of Viral Hepatitis in Europe, WHO, Geneva, 1991
6
Kurane, I., Binn, L.N., Bancroft, W.H. and Ennis, F.A. Human lymphocyte responses to hepatitis A virus-infected cells: Interferon production and lysis of infected cells. J. Immunol. 1985, 135, 2140-2144 7 Vallbracht, A., Gabriel, P., Maier, K., Hartmann, F., Steinhardt, H.J., M011er, C., Wolf, A., Manncke, K.H. and Flehmig, B. Cell-mediated cytotoxicity in hepatitis A virus infection. Hepatology 1986, 6, 13081314
Vaccine, Vol. 10, Suppl. 1, 1992
$131
F. E. A n d r e * , E. D ' H o n d t * , A. D e l e m t a n d
A level o f 10 m l U hepatitis A antibodies/ml as measured by E L I S A is believed to be the minimal protective concentration. I f this level is considered, the mean persistence o f vaccine induced antibodies is approximately 10-11 years after booster dose, 6 - 7 years if only the primary doses are given and 5 - 6 years if the minimal individual titre is taken into account. Keywords: Hepatitis A vaccine; antibody persistence; duration of protection: immunity
INTRODUCTION A study of the persistence of vaccine-induced antibodies to hepatitis A virus (HAV) was performed including calculation of the geometric mean titre after vaccination together with the range of titres, estimation of the disappearance rate of antibodies, and estimation of a minimal protective titre. MATERIALS AND METHODS Inactivated hepatitis A vaccines were prepared from HAV strains CLF and H M i 7 5 , grown on MRC-5 cells, purified, inactivated and adsorbed onto AI(OH)3 as described ~. In a first study group, 110 HAV-seronegative persons were each injected four times, with one of three different doses of the CLF-strain [180, 360 and 720 ELISA units (El.U) at months 0, 1, 2 and 12]. Blood samples were drawn before, and 1 month after, each vaccine dose and at months 6, 12 and 18. In a second study, 69 HAV-seronegative persons received only the 720 EI.U dose (HM175) at months i and 12. Serum samples were drawn before and 1 month after vaccination and at months 6 and 12. The immune response was expressed as percentage seroconversion ( > 20 mIU/ml) and as the geometric mean titre (GMT) of ELISA (mIU/ ml) as described-'. Antibody titres were followed over a period of 12-18 months. For comparison, 23 seronegative persons were passively immunized with standard doses (0.016-0.022 ml/kg) of hepatitis immune globulin (100 IU anti-HAV/ml). Blood samples were drawn 3-5 days later. RESULTS
Immunogenicity and GMTs lmmunogenicity was evaluated with regard to seroconversion and GMT. In the first study three doses of *Institute for Specific Prophylaxis and Tropical Medicine, Kinderspitalgasse 15, Vienna 1095, Austria. *SmithKline Biologicals, Rixensart, Belgium. §To whom correspondence should be addressed 0264-410X/92/100S129-03 (~ 1992Butterworth-HeinemannLtd
vaccine containing the CLF strain were injected following a schedule of vaccination at 0, 1, 2 and 12 months (Table 1). After one injection, a seroconversion rate of ,90% was reached with the two highest doses. After the booster dose at month 12, the G M T was 6578 with the highest dose. Following a schedule of vaccination at 0, 1 and 12 months in the second study with the highest dose of vaccine containing strain HM 175, initial G M T values were lower than in the first study, but after the booster at month 12 there was no statistically significant difference in GMTs between the first and second study (Table 2).
Antibody kinetics The GMTs of blood samples of vaccinees were followed over a period of 18 months in the first, and 12 months in the second, study and the results are shown in Figures 1 and 2. The curves of G M T are roughly parallel indicating disappearance rates independent of antigen dose, vaccine strain and vaccination schedule. From the antibody decrease between months 6 and 12 and 12 and 18 of the first study, the annual decrease rates were calculated. The mean annual disappearance rates in the two periods were 42.5 and 44.3%.
Estimation of minimal protective titre Experience with passive immunization against hepatitis A in > 100 000 travellers 3 has shown that protection could be achieved for at least 3 weeks after administration of 0.015 ml/kg body weight of a hyperimmune globulin (100 IU/ml). This is in accordance with recommendations by the Centers for Disease Control (USA) for 0.02ml immune globulin to be given per kilogram body weight if travel is for < 2 months 4. When this dose was injected into 23 persons with no antibodies against hepatitis A, a mean titre of 21 mIU/ml resulted after 4 days. Since the half-life of passively applied human immune globulins is ~ 21 days, a titre of 10 mIU/ml can be expected after 3 weeks at the end of the protection period 3 and could be considered as a minimal protective concentration. Considering the G M T after immunization with a dose
Vaccine, Vol. 10, Suppl. 1, 1992
$129
Persistence of vaccine-induced anti-HA t~" G. Wiedermann et al. Table 1
Immunogenicity of hepatitis A vaccine (study group 1, strain CLF) Month 1
Month 2
Month 3
Month 6
Month 12
Month 13
Vaccine dose (El.U)
n
SC(%)
GMT
n
SC(%)
GMT
n
SC(%)
GMT
n
SC(%)
GMT
n
SC(%)
GMT
n
SC(%)
GMT
180 360 720
44 50 8
50.0 94.0 87.5
114 293 713
44 50 8
95.5 98.0 87.5
189 387 890
45 50 8
97.8 100 100
478 793 1365
48 49 8
97.8 100 100
317 530 813
45 47 7
97.8 97.9 100
213 429 637
48 47 7
100 100 100
2143 3808 6578
n, Number of persons; SC, seroconverion; GMT, geometric mean titre 2
Table
Immunogenicity of hepatitis A vaccine (study group 2, strain HM175) Month 1
Month 2
Month 6
Month 12
Month 13
Vaccine dose (El.U)
n
SC(%)
GMT
n
SC(%)
GMT
n
SC(%)
GMT
n
SC(%)
GMT
n
SC(%) GMT
720
66
97
278.1
65
98.5
527.6
57
98.2
483.9
65
98.5
268.9
59
100
5059.4
n, Number of persons; SC, seroconversion; GMT, geometric mean titre
I0 000
3 Persistence of anti-HAV after immunization with hepatitis A vaccine (720 El.U) taking into account different decrease rates
Table
E
-~
iooo
L?
Annual decrease (%)
Time to reach the minimal protective level, (years)
50 45 40
9.4 10.9 12.7
aMinimal protective level of 10 mlU/ml 100 I
I
I
I
I
2
3
6
l
I
I
12 13
Time from f i r s t vaccination
18
Although studies of protection achieved in humans have just become available, an inactivated hepatitis A vaccine has already been shown to be protective in chimpanzees 5.
(months)
1 Time course of anti-HAV titres after immunization with three different doses of an inactivated HAV vaccine. Vaccination at 0, 1, 2 and 12 months. 0 , 1 8 0 El.U; I I , 360 El.U; ©, 720 EI.U Figure
10 000 ~
~
O
E I000
F.L3 100 I
I
I
I
I
2
3
6
I
I
12 13
Time from f i r s t vaccination
I
(months)
2 Time course of anti-HAV titres after immunization with doses of 720 EU inactivated hepatitis A vaccine using two different vaccination schedules. Q, Doses at 0, t and 12 months; & , doses at 0, 1, 2 and 12 months
of 720 EI.U and the annual decrease rate as given above, the mean persistence of vaccine-induced antibodies to reach a borderline concentration of 10 m I U anti-HAV /ml would be 10-ll years after the booster, 6-7 years without a booster and 5-6 years if the minimal individual titre is taken into account (Table 3).
Vaccine, Vol. 10, Suppl. 1, 1992
The persistence of vaccine-induced antibodies is believed to be related to the duration of protection. The importance of humoral immunity is emphasized by the experience with passive immunization 3.4. In addition, Vallbracht 7 and Kurane 6 believe that T cells and natural killer cells also play a role in protection. Finally, it can be hypothesized that after primary vaccination and after the disappearance of antibodies, a subsequent infection could induce a booster effect on antibody levels in due time. Krugman and Hilleman (personal communication) have speculated on this and, although it is disputed for hepatitis B, such a hypothesis could also be relevant for hepatitis A. Controlled trials or observations giving information on the duration of immunological memory are needed.
18
Figure
$130
DISCUSSION
ACKNOWLEDGEMENTS These trials were performed in accordance with the provisions of the Declaration of Helsinki. The trial was approved by the ethical commission of the University of Vienna. Written informed consent was obtained from all volunteers before vaccination. REFERENCES 1 2
Andre, F.E., Hepburn, A. and D'Hondt, E. Inactivated candidate vaccines for hepatitis A. Prog. Med. Virol. 1990, 37, 72-95 Wiedermann, G., Ambrosch, F., Kollaritsch, H., Hofmann, H., Kunz, Ch., D'Hondt, E, Delem, A., Andr6, F.E., Safary, A. and Stephenne, J. Safety and immunogenicity of an inactivated hepatitis A candidate vaccine in healthy adult volunteers. Vaccine 1990, 8, 581-584
Persistence of vaccine-induced anti-HA V: G. Wiedermann et al, 3 Ambrosch, F. and Stemberger, H. Impfungen bei Fernreisen Aktueller Stand. Osterr. Arztezcitung 1983, 39, 715-724 4 Center for Disease Control. Recommendations for Protection against Viral Hepatitis. Morbid. Mortal Week. Rep. 1985, 34, 313-335 5 Andre, F.E. and Hepburn, A. Current Status of HA V Vaccine Development Working Group on the Control of Viral Hepatitis in Europe, WHO, Geneva, 1991
6
Kurane, I., Binn, L.N., Bancroft, W.H. and Ennis, F.A. Human lymphocyte responses to hepatitis A virus-infected cells: Interferon production and lysis of infected cells. J. Immunol. 1985, 135, 2140-2144 7 Vallbracht, A., Gabriel, P., Maier, K., Hartmann, F., Steinhardt, H.J., M011er, C., Wolf, A., Manncke, K.H. and Flehmig, B. Cell-mediated cytotoxicity in hepatitis A virus infection. Hepatology 1986, 6, 13081314
Vaccine, Vol. 10, Suppl. 1, 1992
$131
