Hepatitis A Vaccine Immunogenicity 25 Years After Vaccination in Alaska

  • Viral hepatitis and HIV
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Background:
The Hepatitis A vaccine is recommended for children ≥ 1 year old, however the duration of vaccine protection is unknown. In 1991, a cohort of Alaska Native children 3 to 6 years old was recruited to assess initial response to a 3-dose Hepatitis A vaccine series and the duration of protection. We report on the 25 year follow up of the cohort.

Methods:
Participants were randomized to three different schedules: A) 0, 1, and 2 months; B) 0, 1, and 6 months; and C) 0, 1, and 12 months. We assessed IgG antibody concentrations to Hepatitis A virus (anti-HAV) every 2-3 years by calculating the geometric mean concentration (GMC) and proportion of participants with protective levels of anti-HAV (≥ 20 miU/ml) at each time point. We estimated the amount of time until anti-HAV dropped below protective levels using a Kaplan-Meier survival analysis.

Results:
Of the 144 participants, 43 (29.9%) were available at the 25 year follow up period. There was a statistically significant lower GMC among participants who received vaccines on schedule A compared to schedules B and C (A=42.9 miU/ml vs B=100.6 vs C=176.5, P=0.004). Overall, 81.4% (35/43) of participants had protective levels of anti-HAV, a 5.6% decrease from the previous measurement at 22 years after vaccination. In a survival analysis, using data from the entire cohort, 78.7% of participants had protective levels of anti-HAV at 25 years.

Conclusion:
At 25 years following the initial vaccination series, four of five of participants exhibit protective levels of anti-HAV. The high level of protective antibodies in this cohort indicate that supplemental doses of hepatitis A vaccine are not needed at or before 25 years after completion of the vaccine series.

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