INTRODUCTION
Infection with hepatitis B virus (HBV) can cause acute and chronic liver diseases [Reference Liang1, 2]. The virus is transmitted by parenteral or mucosal exposure to infected blood and serous fluids [2, 3]. In highly endemic areas, HBV is most commonly spread from mother to child at birth or through horizontal transmission during the first 5 years of life [3]. Sexual transmission of hepatitis B may occur, particularly in men who have sex with men and heterosexual persons with multiple sex partners or contact with sex workers [3, 4]. Transmission of the virus may also occur through reuse of needles and syringes [3, 4].
It is estimated that 240 million people are chronically infected with hepatitis B and more than 686 000 people around the world die annually due to complications of hepatitis B, including cirrhosis and liver cancer [3–Reference Lozano5].
In 1992, the second generation recombinant DNA hepatitis B vaccine was introduced to the routine immunization programme in Israel and is given since in three doses, at birth, 1 and 6 months of age [Reference Tesher and Somekh6, 7].
Although data on vaccine uptake in Israel are highly available, a few national sero-surveys assessed the seroprevalence of anti-HBs antibodies among the Israeli population following the introduction of HBV vaccine [Reference Hartal8–Reference Michaiel10].
The aim of the present study was to determine the seropositivity rate of anti-HBs antibodies among children and adolescents aged 0–19 years, 19 years following the introduction of the vaccine. In a separate pilot study, we evaluated the seroconversion rate of a group of 17–19 years old adolescents who tested negative to anti-HBs antibodies after the administration of a single dose of HBV vaccine.
METHODS
Study design
We conducted a cross-sectional sero-survey using the Israel national serum bank established in 1997 by the Israel Center for Disease Control. Serum samples from all regions of Israel are collected throughout the year. Serum samples of persons aged <18 years and >55 years are residual samples from diagnostic laboratories, while samples of persons aged 19–55 are collected from both healthy blood donors and residual serum samples from diagnostic laboratories. All 1273 samples collected in 2011 were used for the current study. For each sample, data retrieved were sampling date, date of birth, gender, place of residence, country of birth and ethnic group.
Sampling
Inclusion criteria for the seroprevalence study were all samples collected between January and June 2011 from children and adolescents aged 0–19 years, born after 1 January 1992, the date the vaccine was introduced to the routine immunization programme in Israel. The samples were stratified by gender, the following age groups: 0.00–0·49, 0·50–1·99, 2·00–4·99, 5·00–9·99, 10·00–14·99 and 15·00–19·99 years and by ethnicity. In total, 170 samples were required to detect a difference of 15% or higher in seropositivity rates between age groups with power (1–β) of 80% and α of 0·05.
Booster response evaluation
In a framework of a pilot study, we approached candidates for voluntary national service at the National Blood Services, born after 1 January 1992. These candidates were required to present certificate of hepatitis B vaccination, and an updated anti hepatitis B antibodies level test result as part of the recruitment process. Those who received a full immunization course in infancy and tested negative for anti-HBs antibodies received a booster dose and provided test results for anti-HBs antibodies within 8 weeks after vaccination. A sample size of 31–52 samples was sufficient to demonstrate 98% seropositivity (95% CI: 95–99%) after receiving a booster dose.
Laboratory testing
Anti-HBs antibodies level was determined for each sample using the Vitek Immuno Diagnostic Assay System (VIDAS) Anti-Hbs Total Quick kit, according to the manufacturer's instructions and were expressed in mIU/ml. IgG⩾12 mIU/ml was considered positive, 8⩽IgG<12 mIU/ml intermediate and IgG < 8 mIU/ml was considered negative. Intermediate samples were considered negative for calculating seropositivity rate. Anti-HBc antibodies level was determined using the VIDAS anti-HBc Total II kit, bioMerieux, according to the manufacturer's instructions and were expressed in mIU/ml. IgG < 1 mIU/ml was considered negative, 1·0⩽IgG < 1·4 mIU/ml intermediate and IgG⩾1·4 mIU/ml was considered positive to Anti-HBc. The samples were tested in the Central Virology Laboratory of the Israel Ministry of Health.
Ethic statement
The study was approved by the Institutional Review Board at Sheba Medical Center, Tel Aviv Sourasky Medical Center and Wolfson Medical Center. All participants signed an informed consent.
Data analysis
Seropositivity rates were calculated by age and ethnic group. Analysis of trend was done using the Joinpoint regression analysis applied by the Joinpoint software (the Surveillance Research Program of the US National Cancer Institute, Version 4.4.0) [11]. Differences in the prevalence of seropositivity between subgroups were evaluated using chi-square analyses. The logistic regression model was used to evaluate the association between demographic characteristics and seropositivity, and to calculate odds ratios and 95% confidence interval (CI). Statistical significance was determined using 2-sided test with an alpha level of 0·05. All analyses were performed using SAS software package (version 9.1.3, SAS Institute Inc., Cary, NC, USA).
RESULTS
A total of 1273 samples were tested. Table 1 presents the demographic characteristics of the study population. Of the samples tested, 699 (54·9%) were males, 882 (69·3%) were Jews and 1219 (95·8%) were born in Israel. Totally, 631 (49·6%) samples tested positive for anti-HBs. Seropositivity rate was 37·9% up to age 6 months, followed by a peak at age 6–12 months (Fig. 1). As time elapsed since vaccination in infancy, seropositivity rates declined significantly (P-value < 0·01) reaching 20·7% at age 19 (Annual Percentage Change = −5·7). Table 2 demonstrates the seropositivity rate by demographic characteristics of the study population. No differences in seropositivity rates were observed between Jews and Arabs (P-value = 0·79), males and females (P-value = 0·16) and those born in Israel and others (P-value = 0·11). Age was the only factor significantly associated with seropositivity rate.
Prevalence of anti-HBs antibodies by age.
Socio-demographic characteristics of the study population
Association of seropositivity with socio-demographic characteristics of the study population
In total, 553 samples which were positive to anti-HBs were tested for anti-HBc. In 78 samples, there was not enough sera for further testing. Four samples (1·3%) were anti-HBc positive and 3 (0·5%) were intermediate.
Two hundred and sixteen candidates for voluntary national service, who presented documentation of hepatitis B vaccination in infancy, were approached. 139 (64·4%) of them tested negative for anti-HBs antibodies, and 78 of them (56·1%) received a booster dose as part of the recruitment process. Thirty one (39·7%) of them provided a second blood sample within 8 weeks since vaccination. The mean age and standard deviation of the 31 participants was 17·6 ± 0·6 years, 93·3% were females and 89·3% were born in Israel. Twenty-eight of 31 participants (90·3%; 95% CI: 75·1–96·6%) tested positive for anti-HBs antibodies following vaccination. The three non-responders were all females, Jews, who were born in Israel.
DISCUSSION
In this cross-sectional study we have shown a continuous decline in seropositivity rate of anti-HBs antibodies with time since vaccination. Hepatitis B vaccine is administered to all newborns in Israel in the first 24 h following birth, at 1 month and 6 months.
Vaccination coverage for the third dose was 92–99% between 1992 and 2015 [12, 13]. Taking into account the possibility of vaccine failure, estimated at 3% [Reference Rots14], it is expected that the highest seropositivity rate would be around 90% at the age group 6–12 months following the administration of three doses; indeed the seroprevalence in this age group was 89·5%. We had no information regarding the health status of the study population, and we assume they were healthy. It was shown that children with chronic diseases have lower seroprotective levels in diseased children compared with normal children [Reference El-Asheer15].
Table 3 presents the results of several studies that examined seropositivity rate 10 years and longer after vaccination. In the present study seropositivity rate 10 years following vaccination, was 45·9%, lower compared with reports from other countries (Table 3) [Reference But16, Reference Zanetti17]. Nineteen years following vaccination, seropositivity was 20·7%, lower than reported by China, Egypt, Thailand, Iran, Saudi-Arabia and The Palestinian Authority (Table 3) [Reference But16, Reference Norouzirad18–Reference Qawasmi23] and similar to the USA [Reference Middleman24]. A previous study performed in Israel among male recruits born after 1 January, 1992, evaluated seropositivity rate 18–20 years after vaccination have shown that only 33·7% of male recruits were anti-HBs positive [Reference Hartal8]. The observed differences in seropositivity rates between different studies could be explained by differences in vaccine programmes schedule, type of vaccine (plasma based vs. recombinant) and the number of doses administered.
Seroprevalence of anti-Hepatitis B antibodies in different countries at different time periods after vaccination
The decline in seropositivity with time since vaccination raised the question of the need for a booster dose. Similar to earlier studies [Reference Middleman24–Reference Bagheri-Jamebozorgi26], seropositivity rate following a booster dose was very high (90·3%). Spada et al. demonstrated 98% seroconversion 17 years after vaccination [Reference Spada25], Middleman et al. demonstrated 92% seroconversion 16–19 years after vaccination [Reference Middleman24] and Bagheri-Jamebozorgi et al. demonstrated 90·6% seroconversion 20 years after vaccination [Reference Bagheri-Jamebozorgi26].
Our results were higher than those reported by Hartal, who vaccinated male recruits, 18–20 years after initial vaccination with one dose demonstrated 81·5% seroconversion [Reference Hartal8] and Chaves who challenged the participants 15 years after initial vaccination and demonstrated 71·4% seroconversion [Reference Chaves27]. Although the high seropositivity rate observed among the revaccinated population, it should be kept in mind that 9·7% were still negative.
We have demonstrated low rate (1·3%) of anti-HBc positive samples among those who were anti-HBs positive. Our results are in accordance with previous studies demonstrated hepatitis B breakthrough despite universal vaccination. Saffar et al. reported that 2·5–3·5% of 510 blood samples tested were anti-HBc positive [Reference Saffar21] while Spada et al. in Italy [Reference Spada25] and Alfaleh in Saudi Arabia have shown no samples with anti-HBc positivity [Reference Alfaleh22].
There is still controversy regarding the necessity of a booster dose implementation for risk groups [Reference Chinchai20, Reference Lu28]. Since health care workers, especially surgeons and those engaged in interventional procedures, are at higher risk of various blood-borne infections, including HBV, and high vaccination coverage is needed, we recommend a booster dose for healthcare personnel before starting to work at the health care facility as described [29].
There are several limitations to the present study. (1) Although vaccination rates for HBV are high, we had no information regarding the vaccination history on each sample tested. (2) Since antibody testing after the administration of a booster dose was done within 8 weeks following vaccination, we cannot differentiate whether we observed a booster response or a primary response.
ACKNOWLEDGEMENTS
The authors would like to thank Nadia Pekurovski from the Israel Center for Disease Control, for her assistance in data collection and laboratory assistant and to Dr Veronica Gemdelman and Mrs. Hana Raz from MDA blood services for the blood samples collection. This research received no specific grant from any funding agency, commercial or not-for-profit sectors.
DECLARATION OF INTEREST
None.
