An unprecedented outbreak of acute hepatitis A virus (HAV) infection has been occurring among men who have sex with men (MSM) in Taiwan since June 2015, with more than 750 cases reported to the Taiwan Centers for Disease Control as of 23 September, 2016. We evaluated the effectiveness and serologic response of HAV vaccination in HIV-positive patients in this outbreak setting.
From June 2015 to September 2016, testing for HAV antibodies were prospectively performed for all HIV-positive patients and HAV-seronegative patients were advised to receive 2 doses of HAV vaccines (HAVRIX® or VAQTA®) at an interval of 6 months between the two doses. The primary endpoint of this study was serologic response 4 weeks after the last dose of vaccination and acquisition of acute HAV infection during the follow-up. The secondary endpoint was serologic response at week 48 of vaccination.
During the study period, 1574 HAV-seronegative patients were included, with 94.5% being MSM and median CD4 count 568 cells/mm3. As of 23 September 2016, 1037 patients (65.9%) had received at least one dose of HAV vaccine and 537 (34.1%) declined to receive vaccine; 303 (19.3%) had completed the 2-dose vaccine series. The seroconversion rate at 4 weeks, weeks 5-8, weeks 9-16, and weeks 17-24 was 15.8% (65/411), 25.9% (42/162), 50.3% (86/171), and 50.4% (130/258), respectively. One month after the last dose, the seroconversion rate increased to 94.7%. The factors associated with seroconversion between the first and last doses of HAV vaccination were receiving VAQTA® (adjusted odds ratio [AOR], 2.3; 95% CI, 1.5-3.5), time to anti-HAV IgG testing (AOR, per 1-week increase, 1.1; 95% CI, 1.1-1.2) and previous HAV vaccination (AOR, 32.3; 95% CI, 11.9-87.7). With a total observation duration of 421.5 and 411.5 person-years of follow-up (PYFU), the incidence rate of acute HAV infection in patients without receiving HAV vaccine and those receiving at least 1 dose of HAV vaccine was 11.6 and 0.7 per 100 PYFU, respectively, resulting in vaccine effectiveness of 93.6%. The factors associated with acquisition of acute HAV infection included having not received HAV vaccine (adjusted hazard ratio [AHR], 33.3; 95% CI, 8.9-93.6) and recent syphilis (AHR, 4.7; 95% CI, 2.7-8.3).
Despite the delayed serologic response to HAV vaccination in HIV-positive MSM, the risk of acute HAV infection was significantly reduced by HAV vaccination during the outbreak setting.