Introduction
Hepatitis B virus (HBV) infection is one of the major causes of human morbidity and mortality. It is estimated that at least two billion people are infected worldwide and that more than 350 million are chronic virus carriers; 4.5 million people develop new infections every year, of whom 15–40% will develop cirrhosis, various liver diseases, and hepatocellular carcinomas1.
In addition to measures aimed at improving socioeconomic conditions and hygiene standards (the screening of blood units and blood components, the disinfection and sterilisation of medical and surgical instruments, the introduction and use of disposable equipment, and environmental and hospital education campaigns), the implementation of the mass vaccination programmes recommended by the World Health Organization (WHO) since 1992 has dramatically decreased the incidence of HBV infection among children and adolescents2,3.
As early as 1983, some Italian regions began selective vaccination of people at risk, including intravenous drug users, male homosexuals, people with multiple sex partners, the life partners of HB surface antigen (HBsAg)-positive patients, haemophiliacs, and newly born babies of HBsAg-positive mothers. In 1991 (with Law N. 165 of 27 May 1991, published in the Official Gazette of the Italian Repreprintlic, 1st June 1991), in addition to maintaining selective vaccination of people at risk, vaccination was made compulsory for all children aged 12 years old (limited to the first 12 years of application) and infants in their first year of life4,5, with the aim of creating immunity in childhood or adolescence in order to protect adults whose lifestyles or occupations may increase the risk of infection. By the end of 2010, more than 20 million children had been vaccinated6 and coverage was 95.3% in 20137. This vaccination campaign therefore created two vaccinated populations: those vaccinated at the age of 12 years and those vaccinated during the first year of life.
Numerous studies have been carried out in order to assess and confirm the effectiveness of the vaccination8. Post-vaccination anti-HBs antibody levels of ≥10 mIU/mL are generally considered to be protective8 but, although titres decline over time to undetectable values, this does not indicate a loss of protection and booster vaccine doses are not recommended8–11. Anti-HBs titres and their persistence depend on the number of doses received, the vaccine type, and the route and timing of administration6,8,9,12,13. It has been also observed that lower values are found in subjects vaccinated as infants than in those vaccinated after the first year of life6,9,14. The relative immaturity of the infant immune system could explain the weaker antibody response in subjects vaccinated as infants than in those vaccinated after the first year of life14. However, it is still generally agreed that, regardless of the time of administration, the vaccination induces long-term protection and that there is no need for additional booster doses8,9.
On the other hand, antibody levels in young adults may be important in the field of transfusion as it is necessary to identify donors with high anti-HBs titres (after a booster vaccine dose) for the production of anti-HBs hyperimmune plasma15.
The aim of this study was to evaluate antibody levels in blood donors 18–22 years after they had been vaccinated during the first year of life or at the age of 12 years.
Materials and methods
We examined samples taken from 1,219 consecutive periodic or first-time donors who donated blood or blood components between March and September 2013: 785 males and 434 females, with a mean age of 27.9 years (range, 18–35). One hundred and forty-one (11.6%) had been vaccinated during the first year of life, and 1,078 (88.4%) at the age of 12 years. All of the legally prescribed tests for the validation of blood units and blood components (HBsAg, anti-HCV, anti-HIV 1–2, anti-Treponema pallidum and the molecular biology nucleic acid test for HBV, HIV and HCV) were negative; for the purposes of this study, we also tested the samples for anti-HBs titres and total anti-HBc (aHBs and aHBc VITROS, Ortho Clinical Diagnostics, Buckinghamshire, UK) using the immunofluorescence method.
The seropositivity rates and antibody titres (expressed as geometric mean titres, GMT) were statistically analysed using the chi-squared and Student’s t-test and analysis of variance (ANOVA). All of the analyses were conducted using SPSS software, version 16.0 (SPSS Inc., Chicago, IL, USA).
Results
Nine samples were positive for total anti-HBc (0.7%) and were excluded from further analyses. Of the remaining 1,210 samples (from 780 males and 430 females), 989 (81.7%) were positive for anti-HBs; the GMT was 88.77 mIU/mL.
One hundred and forty donors were vaccinated during the first year of life and for them 18–22 years have passed from vaccination to sampling (group I). One thousand and seventy donors were vaccinated at the age of 12 years with a period from vaccination to sampling of 10–22 years. In particular for 509 of them (47.6%) 18–22 years have passed from vaccination to sampling (group II). We decided to compare only the two groups of subjects with the same 18–22 year time lag between vaccination and sampling.
Irrespectively of their age at vaccination, 506/649 donors (78.0%) were anti-HBs positive (titres ≥10 mIU/mL) with a GMT of 67.75 mIU/mL. Table I shows the anti-HBs results stratified by gender for the two groups. The difference in the percentage of subjects with positive antibody titres between group I and group II was statistically significant, but there was no significant difference between the males and females in the two groups.
Table I.
Proportions of anti-HBs-positive subjects and GMT in donors vaccinated as infants (group I) or adolescents (group II) 18–22 years before, subdivided by gender.
| Vaccination | Anti-HBs | Male | Female | Total |
|---|---|---|---|---|
| During the first year of life (group I) | Positive | 37/72 (51.4%) | 30/68 (44.1%) | 67/140 (47.9%) |
| 95% CI: 39.86–62.94 | 95% CI: 32.30–55.90 | 95% CI: 39.62–56.18 | ||
|
| ||||
| GMT | 9.18 | 7.00 | 8.15 | |
| mIU/mL | 95% CI: 2.51–5.85 | 95% CI: 0.93–13.06 | 95% CI: 3.62–12.68 | |
|
| ||||
| At the age of 12 years (group II) | Positive | 307/363 (84.6%) | 132/146 (90.4%) | 439/509 (86.2%) |
| 95% CI: 80.89–88.31 | 95% CI: 85.62–95.18 | 95% CI: 83.20–89.20 | ||
|
| ||||
| GMT | 111.57 | 149.32 | 121.30 | |
| mIU/mL | 95% CI: 79.18–143.96 | 95% CI: 91.51–207.13 | 95% CI: 92.94–149.66 | |
|
| ||||
| Total | Positive | 344/435 (79.1%) | 162/214 (75.7%) | 506/649 (78.0%) |
| 95% CI: 75.28–82.92 | 95% CI: 69.95–81.45 | 95% CI: 74.81–81.19 | ||
|
| ||||
| GMT | 73.79 | 56.95 | 67.75 | |
| mIU/mL | 95% CI: 69.66–77.92 | 95% CI: 50.32–63.58 | 95% CI: 64.15–71.35 | |
Anti-HBs: antibodies anti-hepatitis B surface antigen; GMT: geometric mean titres; CI: confidence interval.
Table II shows the seropositivity rates stratified according to various antibody titre ranges in the two groups of donors. All of the between-group differences were statistically significant except in the case of the subjects with titres of 10–100 mIU/mL. In particular, the percentage of subjects with anti-HBs titres of >500 IU/mL was significantly higher in group II.
Table II.
Anti-HBs concentrations in donors vaccinated as infants (group I) or adolescents (group II) 18–22 years before.
| Anti-HBs (mIU/mL) | Vaccinated as infants (group I); n=140 | Vaccinated as adolescents (group II); n=509 | p | Total; n=649 |
|---|---|---|---|---|
| Undetectable | 39 (27.9%) | 31 (6.1%) | <0.01 | 70 (10.8%) |
| 95% CI: 20.47–35.33 | 95% CI: 4.0–8.18 | 95% CI: 8.41–13.19 | ||
|
| ||||
| 1 to <10 | 34 (24.3%) | 39 (7.7%) | <0.01 | 73 (11.2%) |
| 95% CI: 17.20–31.40 | 95% CI: 5.38–10.02 | 95% CI: 8.77–13.63 | ||
|
| ||||
| Subtotal ≥ 10 | 67 (47.9%) | 439 (86.2%) | <0.01 | 506 (78.0%) |
| 95% CI: 39.62–56.18 | 95% CI: 83.20–89.20 | 95% CI: 74.81–81.19 | ||
|
| ||||
| 10 to 100 | 51 (36.4%) | 145 (28.5%) | NS | 196 (30.2%) |
| 95% CI: 28.43–44.37 | 95% CI: 24.58–32.42 | 95% CI: 26.67–33.73 | ||
|
| ||||
| 101–1,000 | 15 (10.7%) | 208 (40.9%) | <0.01 | 223 (34.4%) |
| 95% CI: 5.58–15.82 | 95% CI: 36.63–45.17 | 95% CI: 30.75–38.05 | ||
|
| ||||
| >500 | 2 (1.4%) | 139 (27.3%) | <0.01 | 141 (21.7%) |
| 95% CI: 0.00–3.35 | 95% CI: 23.43–31.17 | 95% CI: 18.53–24.87 | ||
|
| ||||
| >1,000 | 1 (0.7%) | 86 (16.9%) | <0.01 | 87 (13.4%) |
| 95% CI: 0.00–2.08 | 95% CI: 13.64–20.16 | 95% CI: 10.78–16.02 | ||
Anti-HBs: antibodies anti-hepatitis B surface antigen; CI: confidence interval.
Discussion
The mass anti-HBV vaccination campaign in Italy drastically decreased the incidence of acute hepatitis in new generations16,17. However, the administration of the vaccine during the first year of life and at the age of 12 years has created two newly vaccinated populations (the former of which is steadily increasing whereas the latter will not increase anymore as the series of vaccinations was completed in 2004). As previously reported in the literature10,14, we found that anti-HBs seropositivity rates and antibody titres are significantly higher in the population vaccinated at the age of 12 years.
It is likely that administering the vaccine at birth somehow affects antibody production, which can also be influenced by the type of vaccine used. For example, a hexavalent vaccine (anti-diphtheria, tetanus, pertussis, polio, hepatitis B and Haemophilus influenzae) which had been licensed in Europe in 2000, was withdrawn in 2005 because of its allegedly poor immunogenicity13: although it was demonstrated that immune memory persisted, the antibody titres were lower than those obtained with other types of vaccine8,13. However, none of the subjects in our study had been vaccinated with a hexavalent vaccine between 2000 and 2005 because they were still too young to enter blood donation programmes.
It is widely accepted in the literature that the vaccination is effective at inducing an immune memory and that people with anti-HBs titres lower than those considered protective do not need to receive any additional booster doses. Some authors however divide subjects with titres of less than 10 mIU/mL into those with residual levels of anti-HBs (titre of ≥1 or ≥2 mIU/mL, which may predict an anamnestic response once a booster dose is given) and those with undetectable level (or <2 mIU/mL), which are predictive of no response18,19. We found a statistically significant difference between the percentage of subjects in our two study groups with titres of ≤1 mIU/mL, which may indicate a higher rate of non-responses among people vaccinated during the first year of age but, as they were not given a booster dose, this remains a speculative hypothesis. It should be noted that non-responders are declared as such when two full vaccination series fail.20
However, even if vaccinated subjects can be considered protected regardless of their anti-HBs titres, there may be a number of other implications once they enter a blood component donation programme. Donors with high antibody titres can be selected to donate blood for the production of anti-HBV hyperimmune plasma and anti-HBV immunoglobulins. In our Centre, using a cut-off antibody titre >500 mIU/mL15, only 1.4% of the donors vaccinated during the first year of life would be selected against 27% of those vaccinated at 12 years. Furthermore, if the cut-off titre were raised to >1,000 mIU/mL, the corresponding figures would be <1% and about 17%, respectively.
Conclusions
In order to optimise economic resources, the screening for donors with high anti-HBs titres eligible to receive a HBV vaccine booster dose for the production of hyperimmune anti-HBV plasma by plasmapheresis should concentrate on donors vaccinated at the age of 12 years.
Acknowledgements
We would like to thank Dr. Andrea Boselli, Department of Laboratory Medicine, Luigi Sacco Hospital, Milan, and Dr. Cristina Morazzoni, Microbiology Unit, Hospital of Legnano, Italy, for the statistical analysis.
Footnotes
Authorship contributions
All Authors contributed equally to the study and approved the final version of the paper.
The Authors declare no conflicts of interest.
References
- 1.Lavanchy D. Worldwide epidemiology of HBV infection, disease burden, and vaccine prevention. J Clin Virol. 2005;34(Suppl 1):S1–3. doi: 10.1016/s1386-6532(05)00384-7. [DOI] [PubMed] [Google Scholar]
- 2.World Health Organization. WHO expanded programme on immunization. Report of the 13th Global Advisory Group Meeting; 1990. [Accessed on 15/02/2015]. Available at: http://apps.who.int/iris/bitstream/10665/60863/1/WHO_EPI_GEN_91.3.pdf. [Google Scholar]
- 3.Ni YH, Huang LM, Chang MH, et al. Two decades of universal hepatitis B vaccination in Taiwan: impact and implication for future strategies. Gastroenterology. 2007;132:1287–93. doi: 10.1053/j.gastro.2007.02.055. [DOI] [PubMed] [Google Scholar]
- 4.Piazza M, Da Villa G, Picciotto L, et al. Mass vaccination against hepatitis B in infants in Italy. Lancet. 1988;2:1132. doi: 10.1016/s0140-6736(88)90540-5. [DOI] [PubMed] [Google Scholar]
- 5.Zanetti AR, Tanzi E, Romanò L, Grappasonni I. Vaccination against hepatitis B: the Italian strategy. Vaccine. 1993;11:521–4. doi: 10.1016/0264-410x(93)90222-j. [DOI] [PubMed] [Google Scholar]
- 6.Stroffolini T, Guadagnino V, Caroleo B, et al. Long-term immunogenicity of hepatitis B vaccination in children and adolescents in a southern Italian town. Infection. 2012;40:299–302. doi: 10.1007/s15010-011-0233-2. [DOI] [PubMed] [Google Scholar]
- 7.Ministery of Health, Italy. Infection Disease and Vaccination. Vaccination coverage. Ministery of Heath website. [Accessed on 15/02/2015]. Available at: http://www.salute.gov.it/imgs/C_17_pagineAree_811_listaFile_itemName_17_file.pdf.
- 8.FitzSimons D, Hendrickx G, Vorsters A, Van Damme P. Hepatitis B vaccination: a completed schedule enough to control HBV lifelong? Milan, Italy, 17–18 November 2011. Vaccine. 2013;31:584–90. doi: 10.1016/j.vaccine.2012.10.101. [DOI] [PubMed] [Google Scholar]
- 9.Zanetti AR, Mariano A, Romanò L, et al. Long-term immunogenicity of hepatitis B vaccination and policy for booster: an Italian multicentre study. Lancet. 2005;366:1379–84. doi: 10.1016/S0140-6736(05)67568-X. [DOI] [PubMed] [Google Scholar]
- 10.European Consensus Group on Hepatitis B Immunity. Are booster immunisations needed for lifelong hepatitis B immunity? Lancet. 2000;355:561–5. [PubMed] [Google Scholar]
- 11.Gabbuti A, Romanò L, Blanc P, et al. Long-term immunogenicity of hepatitis B vaccination in a cohort of Italian healthy adolescents. Vaccine. 2007;25:3129–32. doi: 10.1016/j.vaccine.2007.01.045. [DOI] [PubMed] [Google Scholar]
- 12.Sernia S, Ortis M, Antoniozzi T, et al. Levels of anti-HBs antibody in HBV-vaccinated students enrolled in the Faculty of Medicine, Dentistry and Health Professions of a large Italian university. Biomed Res Int. 2015 doi: 10.1155/2015/712020. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 13.Zanetti AR, Romanò L, Giambi C, et al. Hepatitis B immune memory in children primed with hexavalent vaccines and given monovalent booster vaccines: an open-label, randomised, controlled, multicentre study. Lancet Infect Dis. 2010;10:755–61. doi: 10.1016/S1473-3099(10)70195-X. [DOI] [PubMed] [Google Scholar]
- 14.Chiara F, Bartolucci GB, Mongillo M, et al. Hepatitis B vaccination at three months of age: a successful strategy? Vaccine. 2013;31:1696–700. doi: 10.1016/j.vaccine.2013.01.046. [DOI] [PubMed] [Google Scholar]
- 15.Velati C, Scudeller G, Romanini G, et al. [First Research Project “Blood” (1998)- Progress report]. Rapporti ISTISAN 99/9 National Institute of Health; Italy: pp. 9–14. [In Italian.] [Google Scholar]
- 16.Stroffolini T, Mele A, Tosti ME, et al. The impact of the hepatitis B mass immunisation campaign on the incidence and risk factors of acute hepatitis B in Italy. J Hepatol. 2000;33:980–5. doi: 10.1016/s0168-8278(00)80132-4. [DOI] [PubMed] [Google Scholar]
- 17.Mele A, Tosti ME, Mariano A, et al. Acute hepatitis B 14 years after the implementation of universal vaccination in Italy: areas of improvement and emerging challenges. Clin Infect Dis. 2008;46:868–75. doi: 10.1086/528687. [DOI] [PubMed] [Google Scholar]
- 18.Chiara F, Bartolucci GB, Cattai M, et al. Hepatitis B vaccination of adolescents: significance of non-protective antibodies. Vaccine. 2013;32:62–8. doi: 10.1016/j.vaccine.2013.10.074. [DOI] [PubMed] [Google Scholar]
- 19.Spradling PR, Xing J, Williams R, et al. Immunity to hepatitis B virus (HBV) infection two decades after implementation of universal infant HBV vaccination: association of detectable residual antibodies and response to a single HBV challenge dose. Clin Vaccine Immunol. 2013;20:559–61. doi: 10.1128/CVI.00694-12. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 20.Advisory Committee on Immunization Practices; Centers for Disease Control and Prevention (CDC) Immunization of health-care personnel: recommendations of the Advisory Committee on Immunization Practices (ACIP) MMWR Recomm Rep. 2011;60(RR-7):1–45. [PubMed] [Google Scholar]