Epi-Update
Vaccine-Induced Hepatitis B Immunity among Canadian Street Youth (1999-2005)

Introduction

Hepatitis B is a serious disease caused by a virus that attacks the liver. The virus, which is called hepatitis B virus (HBV), can cause lifelong infection, cirrhosis (scarring) of the liver, liver cancer, liver failure, and death.  In Canada, the prevalence is estimated to be between 0.7% and 0.9% and the distribution of cases varies by ethnic origin and risk group. The highest incidence of the disease is seen in teenagers and young adults^{1, 2}. Infection routes include sexual contact with an infected person and exposure to needle sticks and other 'sharps' which have been contaminated with HBV (this includes people who inject drugs). Mother to child transmission is also possible^{3, 4}.

Hepatitis B is also a vaccine-preventable blood-borne infection. A safe and effective vaccine against HBV infection has been available since the early 1980s.  As of March 2002, 151 countries have introduced hepatitis B vaccine within their national immunization programs¹. To prevent hepatitis B in Canada, a comprehensive strategy has been developed which includes vaccination of infants, vaccination of pre-adolescents aged 9-13 through school-based programs and recommended vaccination of individuals at increased risk such as men who have sex with men, persons with a recent history of sexually transmitted infections (STIs) or multiple sexual partners, injection drug users, inmates of correctional facilities, household and sexual contacts of HBV-infected persons, and health care and emergency service workers and pregnant women ⁵. In Canada, all 13 provinces and territories had implemented a universal immunization program against HBV by 1998⁶. The implementation of this vaccination program has greatly contributed to the decrease in hepatitis B infection in the general population. However, the risk of HBV infection remains high for certain populations including immigrants from countries where HBV is endemic, street-involved youth, injecting drug users, and sex trade workers.

Street-involved youth are particularly vulnerable to HBV infection because of unstable living conditions, violence, substance abuse, and other factors that may prevent them from accessing the basic services provided through the public health and/or education systems. These social and contextual factors may also place them at higher risk for substance abuse and unsafe sexual practises that are associated with the transmission of sexually transmitted blood borne infections, including HBV⁷. Few studies, however, have focused on the level of vaccine-induced immunity to HBV in this population.

The purpose of this update is to examine the trend in the proportion of street-involved youth who have vaccine-induced immunity to HBV and its associated determinants. Information presented is based on the data collected by the Enhanced Canadian Street Youth Surveillance (E-SYS) program from 1999 to 2005. E-SYS is an ongoing, multi-centre enhanced surveillance system that describes changing patterns of sexually transmitted blood borne infections (STBBIs) and associated determinants and contextual factors among street-involved youth in Canada. A total of 4,035 participants, recruited from six sites (Halifax, Ottawa, Toronto, Saskatoon, Edmonton, and Vancouver), who had definitive testing results of anti-HBs and anti-HBc were included in the analysis. Vaccine-induced immunity was identified by blood test results of anti-HBc negative and anti-HBs positive.

Results from E-SYS

Vaccine-induced HBV immunity: The proportion of youth who had vaccine-induced immunity to HBV has almost doubled from 1999 to 2005, but the overall proportion remains low.

• Overall, 51.7% of street-involved youth had vaccine-induced HBV immunity.
• The proportion of vaccine-induced HBV immunity has significantly increased from 34.7% in 1999 to 64.4 % in 2005 (p<0.001).
• Overall, 58.6% of street-involved youth between 15-19 years of age and 42.3% of 20-24 year olds had vaccine-induced HBV immunity. There was a higher percentage increase in vaccine-induced immunity in the younger age group compared to the older age group. 
• The increase in proportion of street-involved youth with vaccine-induced HBV immunity occurred across all sites but there were site specific differences in the overall proportion of study participants with vaccine-induced HBV immunity from 23.8% to 58.6%.

Vaccine-induced HBV immunity demographics: Vaccine-induced HBV immunity was significantly lower among street-involved youth who were older, male, and had lower levels of education (Table 1).

• Other factors examined, which were not significantly associated with vaccine-induced HBV immunity, included country of birth and ethnicity.

 

Table 1: Vaccine-induced HBV immunity demographics

Characteristic	Number with Immunity (%)	OR (95% CI)*	P-value
Age (year)
15-19	1370 (58.6)	1.93 (1.70, 2.20)	<0.0001
20-24	718 (42.3)	Ref
Gender
Male	1226 (48.1)	1.50 (1.32, 1.70)	<0.0001
Female	861 (58.1)	Ref
Highest education level attained
Primary (up to grade 6)	47 (43.1)	Ref
Secondary (up to grade 12) or above	2029 (52.3)	1.44(0.98, 2.12)	0.059

*OR (95% CI) = odds ratio (95% confidence interval)

Vaccine-induced HBV immunity was significantly lower among street-involved youth who reported being in a jail or a remand centre or who had not lived with their parents for more than one year (Table 2).

• Other factors examined, which were not significantly associated with vaccine-induced HBV immunity, included ever having a social worker and having been in foster care and/or in a group home.

 

Table 2: Factors associated with vaccine-induced immunity

Characteristic	Number with Immunity (%)	OR (95% CI)*	P-value
Not living with parents for > 1 year	1037 (53.7)	1.36(1.17, 1.57)	<0.01
Living with parents/not living with parents for <1 year	711 (61.1)	Ref
Ever been in detention centre, prison or jail:
Yes	1157 (49.2)	Ref
No	923 (55.3)	1.18 (1.13, 1.45)	<0.001

*OR (95% CI) = odds ratio (95% confidence interval)

Vaccine-induced HBV immunity was significantly lower among street-involved youth who reported ever being tattooed. 

• The immunity level was 54.0 % for street youth who had ever been tattooed vs. 59.4% for those who had not been tattooed (p<0.01).
• Other factors examined which were not significantly associated with HBV immunity included: smoking, drinking, binge drinking, injecting drug use (IDU), non-injecting drug use, clean equipment use for IDU and non-IDU and body pierced.

Vaccine-induced HBV immunity was significantly higher among street-involved youth who reported same sex behaviour and who had previous STIs based on physician’s diagnosis (Table 3).

• Tests for sexual behaviours were conducted for phase 4 and 5 only due to data availability.

• Other behaviours examined, which were not significantly associated with HBV immunity, included: age at first sexual activity, condom use, obligation sex, trade sex, sex with a STI sufferer or drug user in the past three months and prior STI diagnosed due to contact tracing based on partners’ positive test results.

 

Table 3: Sexual health and STI diagnosis associated with vaccine-induced immunity

Characteristic	Number with Immunity (%)	OR(95% CI)*	P-value
Same sex behaviour:
Yes	324 (65.9)	1.31(1.06,1.62)	0.012
No	962 (59.5)	Ref
Ever had STIs by doctors diagnosis:
Yes	322(66.3)	1.34(1.08,1.66)	0.007
No	967(59.5)	Ref

*OR (95% CI) = odds ratio (95% confidence interval)

Discussion

The proportion of vaccine-induced immunity to HBV among street-involved youth participating in E-SYS has almost doubled from 34.7% in 1999 to 64.4% in 2005. However, the overall prevalence of vaccine-induced HBV immunity levels among street-involved youth participating in E-SYS is low considering that the reported vaccination completion rate of more than 90% among pre-adolescent population in Canada³.

The reasons for the low levels of vaccine-induced immunity to HBV among street-involved youth are not clear given that the universal immunization program has been implemented across Canada since the mid-1990s. It is possible that low levels of immunity may be present among a subset of the E-SYS participants since assessment of anti-HBs titres did not occur as part of the E-SYS. However, there may be certain areas where vaccination coverage is less than optimal. Youth who participated in E-SYS may have been too old to have benefited from the introduction of the infant immunization program. Certain youth residing in these “low vaccine coverage” areas may not have benefited from the universal vaccination programs. School drop-out rates and intermittent school attendance may also adversely affect the levels of HBV immunization offered through school-based vaccination programs. 

Vaccination is a safe and effective approach to HBV infection prevention. Results from E-SYS and other studies confirm that street-involved youth continue to be at risk for HBV infection. Therefore there is a need for creative outreach programs to access and increase vaccine coverage in this key population. Health care providers need to continue to verify vaccination status and offer vaccinations to adolescents when they come in for medical check-ups. Prevention messaging around risk behaviours for HBV transmission such as unsafe sexual activity, tattooing, and injecting drug use need to be adapted to grab the attention of street-involved youth, especially those who are male and over 20 years of age.

References

1. World health Organization. Hepatitis B. Geneva, World Health Organization, 2002.
   http://www.who.int/entity/csr/disease/
   hepatitis/HepatitisB_whocdscsrlyo2002_2.pdf
2. Beech BM, Myers L, Beech DJ, et al. Human immunodeficiency syndrome and hepatitis B and C infections among homeless adolescents.  Semin Pediatr Infect Dis 2003;14(1):12-9.
3. Zhang J, Zou SM, Giulivi A.  Hepatitis B in Canada. CCDR Volume 27S3, Sept 2001. Available from:
   http://www.phac-aspc.gc.ca/hcai-iamss/bbp-pts/pub-eng.php
4. Mast EE, Margolis HS, Fiore AE, et al. A comprehensive immunization strategy to eliminate transmission of hepatitis B virus infection in the United States: recommendations of the Advisory Committee on Immunization Practices (ACIP) part 1: immunization of infants, children, and adolescents. MMWR Recomm Rep 2005 Dec 23;54(RR-16):1-31
5. Public Health Agency of Canada. Canadian Immunization Guide Seventh Edition – 2006.
   http://www.phac-aspc.gc.ca/publicat/cig-gci/p04-hepb-e.html.
6. Canadian Nursing Coalition on Immunization (CNCI). National Surveys of Provincial and Territorial Immunization Programs
   http://www.immunize.cpha.ca/english
   /consumer/consrese/pdf/ptscheduleMay04.pdf
7. Boivin JF, Roy E, Haley N, et al. The health of street youth: a Canadian perspective. Can J Public Health 2005;96:432-7.

Acknowledgements

Enhanced Canadian Street Youth Surveillance is possible as a result of collaboration between the Public Health Agency of Canada and researchers, provincial and local health authorities and community based organisations from participating sites across Canada. The organisations and people associated with E-SYS can be retrieved at http://www.phac-aspc.gc.ca/sti-its-surv-epi/youth-jeunes-eng.php. Special thanks to the street-involved youth who consented to participate in E-SYS.

For more information, please contact:

Surveillance and Epidemiology Section
Community Acquired Infections Division
Centre for Communicable Disease and Infection Control
Tunney’s Pasture
Postal Locator: 0603B
Ottawa, Ontario K1A 0K9
Fax: (613) 941-9813