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Hepatitis A vaccination is effective in preventing disease. However, the duration of protection after vaccination is unknown.We enrolled persons who responded to a 3-dose primary series of hepatitis A vaccine. For adults, the first dose was 720 ELISA units (EU) of hepatitis A vaccine, readministered at 1 and 12 months after the first vaccination (hereafter, “0-1-12 months”); for children aged 3-6 years, the first dose was 360 EU, readministered according to 1 of 3 vaccination schedules: 1 and 2 months after the first vaccination (“0-1-2 months”), 1 and 6 months after the first vaccination (“0-1-6 months”), or 1 and 12 months after vaccination (“0-1-12 months”). Specimens collected 1 month and 1-10 years after vaccination were tested for antibody to hepatitis A virus (anti-HAV) by ELISA. Long-term antibody persistence was estimated by using the observed rate of decline in geometric mean concentration (GMC).A total of 144 children and 128 adults were enrolled. Children vaccinated at 0-1-2 months had a significantly lower GMC of antibody than children vaccinated at 0-1-12 months, but this difference was statistically significant only through 4 years of follow-up. All 67 children tested at 10 years and 25 (96%) of 26 adults tested at 8-9 years had detectable anti-HAV. The estimated duration of antibody persistence was 21-27 years, depending on the vaccination schedule.Anti-HAV persists in adults and children for more than 10 years after the primary vaccination series. Additional studies are needed to evaluate the duration of antibody persistence beyond 10 years and to assess the long-term immunogenicity of the currently recommended 2-dose schedule.