The hepatitis B vaccine has dramatically reduced the rate of new HBV infections. Two recent studies provide further information about how the vaccine promotes immune response and how long protection lasts.

T-Lymphocyte Frequency and Function

The first study, reported at the 2006 Digestive Disease Week conference in Los Angeles, looked at T-cell activation after vaccination.

The researchers enrolled 10 subjects who received three doses of the Engerix-B DNA-recombinant HBsAg vaccine administered a baseline and at one and six months, as well as 10 healthy controls. CD3, CD4, and CD25 T-lymphocytes were measured in peripheral blood using flow cytometry, and T-lymphocytes activity was assessed using immunomagnetic sorting.

Results

After one month, vaccinated individuals achieved a protective titer of anti-HBs antibodies (> 100 IU/mL).

These subjects experienced a statistically significant increase in CD4 and CD25 T-lymphocyte number and function, compared with both pre-vaccination levels and levels observed in patients with chronic hepatitis B (P < 0.05).

Conclusion

The researchers concluded that an increase in CD3, CD4, and CD25 T-cell frequency and function appeared one month after vaccine administration when a protective antibody titer was achieved, suggesting that CD4/CD25 T-lymphocytes play a role in seroconversion. They proposed that these cells might be used as a marker to monitor antiviral treatment response.

Long-Term Protection

The second study, reported in the June 1, 2006 Journal of Infectious Diseases, looked at long-term protection against HBV infection and carriage after infant vaccination. The researchers noted that infant vaccination has been effective in preventing horizontal transmission during early childhood, but it is not known whether protection is maintained into adulthood.

The study analyzed data from participants aged 1-24 years in two rural villages in Gambia, where early childhood HBV vaccination was introduced in 1984. The study was conducted in 2003, and included 81.5% of 1350 eligible participants.

Results

Overall vaccine efficacy against HBV infection was 83.4% (95% CI 79.8%-86.6%).

Efficacy against HBV carriage was 96.5% (85% CI 93.9%-98.9%).

Vaccine efficacy against infection was similar when restricted to primary responders (85.3%).

A significant effect of peak antibody concentration was observed.

Both vaccine efficacy and levels of hepatitis B surface antibody (anti-HBs) decreased with age.

Among participants aged 20-24 years, vaccine efficacy against HBV infection was 70.9% (95% CI 60.4%-80.5%) and efficacy against HBV carriage was 91.1% (95% CI 75.8%-100%).

Fifteen years after vaccination, fewer than half of the vaccinated individuals still had detectable anti-HBs.

The prevalence of HBV carriage in the unvaccinated population was similar to the prevalence observed 20 years earlier in the pre-vaccination era.

Conclusion

The researchers concluded that vaccination early in life can provide long-lasting protection against HBV carriage, despite decreasing antibody levels. They added that the need for, and usefulness of, "booster" vaccines should be evaluated.

6/16/06

References

A Perrella, L Racioppi, L Atripaldi, and others. HBV vaccination with evidence of protective antibodies titer induces CD4+/CD25+ T cells. Abstract T1857. Digestive Disease Week 2006. May 20-25, 2006. Los Angeles, CA.

MAB van der Sande, P Waight, M Mendy, and others. Long-term protection against carriage of hepatitis B virus after infant vaccination. Journal of Infectious Diseases 193(11): 1528-1535. June 1, 2006.