Hepatitis B vaccination provides long-term protection
through 30 years for a majority of recipients, and more than 90% were protected
with either initial immunisation or a booster, according to a presentation at The Liver Meeting 2013, the 64th
annual meeting of the American Association for the Study of Liver Diseases
(AASLD), earlier this month in
Washington, DC.
Over years or decades, chronic hepatitis B
virus (HBV) infection can lead to serious liver disease including cirrhosis and
liver cancer. Hepatitis B is endemic in some parts of the world, especially in
Asia and Africa, where it is often transmitted from mother to child. The
widespread implementation of infant HBV vaccination, however, has reduced
hepatitis B incidence in many countries worldwide.
Michael Bruce of the Centers for Disease Control and Prevention's
Arctic Investigations Program presented long-term
findings from the Alaska HBV Vaccine Demonstration Project, or Vax Demo. In the
1970s, the Alaskan Native population had the highest rate of hepatitis B in the
US and one of the highest rates in the world, he noted as background.
Starting in 1981, the Vax Demo project
immunised more than 1500 Yupik Eskimo children (aged six months and older) and
adults in 16 villages in western Alaska. Participants in the project received three doses of
the first commercially available HBV vaccine, made from inactivated virus
obtained from plasma of infected individuals. In the late 1980s, this early
vaccine was replaced with a safer recombinant or genetically engineered
formulation (Merck's Recombivax).
Within five years of the start of the
programme, the incidence of symptomatic hepatitis B declined dramatically in the
immunised population, from about 200 to less than 20 cases per 100,000 people.
Vax Demo researchers have followed this
population for more than 30 years to determine how long vaccine protection
lasts. Among 1530 children and adults who responded to the initial immunisation
series, a majority continued to have protective hepatitis B surface antibody
(anti-HBs) levels of at least 10mIU/ml:
- 5 years: 81%;
- 7 years: 74%;
- 15 years: 66%;
- 22 years: 60%.
At the 22-year follow-up – which included
a subset of vaccinated individuals in seven villages – people whose anti-HBs
levels fell below 10mIU/ml were given a 10mcg Recombivax booster dose to test their immune response.
A total of 16 breakthrough HBV infections
occurred, but there were no new breakthroughs after the 15-year follow-up. None
of these infections were symptomatic and none become chronic.
The 30-year follow-up looked at residents
of 13 villages who took three doses of the initial vaccine with documented
response and received no additional boosters besides the 22-year follow-up
dose. Again, a booster was administered to people who fell below the 10mIU/ml
threshold at the 30-year evaluation.
Vax Demo 30 included 435 eligible
participants. Of these, 129 people did not get a booster at the 22-year
follow-up, 63 people did receive the 22-year booster and 243 people did not
participate in Vax Demo 22.
Overall, 219 participants, or 50%, still
had anti-HBs levels of 10mIU/ml or higher at 30 years. Sustained response rates
were 66% for those without the 22-year booster, 14% for those who received the
22-year booster and 51% for those who were not tested at 22 years. Again, no
symptomatic acute or chronic HBV infections were identified at the 30-year
follow-up.
People who attained higher anti-HBs
antibody levels after the initial vaccine series were more likely to retain
protective levels at 30 years:
- 10-100 mIU/ml after primary series: 20%
with sustained protective levels;
- 100-1000 mIU/ml: 34%;
- 1000-5000 mIU/ml: 58%;
- >5000 mIU/ml: 88%.
Bruce noted that significant differences
in sustained protection according to age were observed, but final data are not
yet available. There was no association between protective antibody levels and
sex, body mass index, diabetes, cancer or use of immune-modulating drugs.
Among people who had antibody levels below
10mIU/ml and received a booster dose for the first time at 30 years, 92% who
had adequate levels at year 22 and 88% who were not tested at year 22 achieved
protective levels one month after boosting. (People who received a booster at
22 years were not boosted again, even if their antibody levels remained low.)
In summary, the researchers noted that
antibody levels continued to decline over time, as did the proportion of
participants with adequate levels, which fell from 81% at 5 years to 51% at 30
years. However, 88% of participants achieved adequate antibody levels after the
30-year booster.
"Overall, 94% had evidence of
immunity" either with or without boosting, they stated. "Higher
anti-HBs after primary series was associated with protective antibody levels at
30 years."
Based on these results, they concluded, "Protection by
primary immunisation with plasma-derived hep B vaccine
lasts at least 30 years" and "booster doses [are] not needed."
Bruce said that these findings would likely also apply to
people vaccinated with the current recombinant vaccine.