Dramatic reduction in hepatitis B through school-based immunization without a routine infant program in a low endemicity region

Notifiable disease trends: acute and chronic HB report rates, 1990–2013

Between 1990–2013, the overall incidence of acute-HB cases per 100,000 decreased by
97 % from 6.5 to 0.2 (p0.0001), (Fig. 1). In children ?9 yoa, the acute-HB incidence decreased from 0.6 in 1990 to no cases
since 2010 (p??0.0001). In those 10–19 yoa, the incidence of 3.2 in 1990 also decreased
to zero since 2007 (p??0.0001). Finally, in adults 20–29 yoa, the incidence of 15
per 100,000 in 1990, formerly the highest of all age groups, also fell to zero in
2013 (p??0.0001).

Fig. 1. Reported rate per 100 000 person-years of acute, chronic and unspecified hepatitis
B cases

During the same period, the overall rate of newly-reported chronic-HB cases per 100,000
decreased by 66 % from 17.7 to 6.1 (p??0.0001), with a reduction of 92 % (2.4 to
0.2;p??0.001) in children???9 yoa and 83 % (7.2 to 1.2;p?=?0.003) in those 10–19 yoa. The rate of unspecified case reports showed an initial
downward then upward trend during the study period. However, rates were low and stable
throughout in children???9 yoa (0.3 vs. 0.2;p?=?0.70) and 10–19 yoa (1.6 vs. 1.5;p?=?0.45) old (Fig. 1). The upward trend in unspecified case reports since 2004 was among adults ?20 yoa
and primarily 30–39 yoa (Fig. 1).

Acute-HB case reports – potential for prevention through infant immunization

Among children ?9 yoa, there were 9 acute-HB case reports during the 2005–2013 period,
all before 2010 and of whom 8 would not have been preventable by routine universal
infant immunization. Five children had been adopted from HB-endemic countries and
were already infected upon arrival in Canada. Three children were born in Quebec from
HBsAg-positive mothers: two had received immunoglobulin at birth and 3 or 4 doses
of vaccine according to the recommended schedule. The parents of the third child refused
prenatal screening; the mother was identified to be HBsAg-positive 2 months post-delivery
and the child was diagnosed with HB a few months after birth. The final acute HB case
was born in another Canadian province and was diagnosed at preschool age. The mother
was born in a highly-endemic country but her HBsAg status and the child’s age upon
arrival in Quebec were unknown. Assuming that this latter case was preventable, then
over and above the existing program, an infant immunization program could have spared
0.0249 acute-HB cases per 100,000 person-years (CI:0.0248-0.0251) in children ?9 yoa
between 2005 and 2009 and none between 2010 and 2013.

There were two acute-HB cases reported in individuals 10–19 yoa between 2005 and 2013;
both occurred before 2008. The first was an unvaccinated homosexual boy born in Quebec;
the second was a drug user with no information on country of birth or vaccination
status. In addition to school-based HB vaccine-eligibility, these two individuals
would have been eligible for immunization on the basis of high-risk behaviours but
assuming infant immunization may have spared their infection, this would correspond
to an additional preventable rate of 0.0654/100,000 person-years (CI:0.0651-0.0657)
between 2005 and 2007 in that age group, and none between 2008 and 2013.

Overall, in addition to the existing program, an infant immunization program could
have prevented 0.0335 (95 % CI: 0.0334-0.0336) acute-HB cases per 100,000 person-years
between 2005 and 2009 in people 0–19 years old.

Chronic-HB and unspecified cases – risk factors

With no acute-HB case reported in children ?9 yoa since 2010, we limited the analysis
of risk factors among chronic cases to the period spanning 2005–2009.

Among the 38 chronic-HB cases reported in children ?9 yoa, 34 (89 %) were born outside
Quebec, three were born in Quebec and one lacked place-of-birth information. The three
Quebec-born children had known HBsAg-positive mothers, received adequate vaccination
and immunoglobulin at birth and were not preventable. Among the 34 (89 %) immigrant
cases, 13 were already infected upon arrival in Canada or diagnosed with chronic-HB
during the first 12 months thereafter; 9 had unknown HBsAg status at arrival but were
born from a known HBsAg-positive mother; and one was fully vaccinated before arrival.
For the other 11 cases there was insufficient information to explain when and how
they became infected.

In the 10–19 yoa group, there were 118 chronic-HB cases reported between 2005 and
2009. Of these, 9 cases were born in Quebec and 109 cases (92 %) were born outside
Quebec (n?=?84) or with unknown place of birth (n?=?25). Among individuals born in Quebec, 2 were born to HBsAg-positive mothers, 2
had HBsAg carriers among their family members, 2 reported unsafe sex, 2 had parents
born in an endemic country with unknown HB status and one did not report any risk
factor. The two cases born to HBsAg-positive mothers were probably infected at birth
and would likely not have been prevented by an infant program starting at 2 months
of age. Among the other 109 chronic-HB cases, 80 (68 %) were born in a high-endemicity
country, 2 had HBsAg carriers among their family members, 2 were born to an HBsAg-positive
mother, and 1 reported sexual aggression as a potential cause of infection.

In addition, there were 15 case reports in people 10–19 yoa with unspecified acute
or chronic HB status, 5 of whom were born in a high-endemicity country and another
whose parents were born in an endemic country. For the other 9 unspecified cases,
there was no information on country of birth or other risk factors.

Globally, among the 182 cases reported in those ?19 yoa, 133 cases were born outside
Quebec, 122 (91 %, CI:87 %-96 %) of whom were born in an endemic country.