CD4 and hepatitis A virus infection: All case patients were MSM with a median age of 30 years and baseline CD4 count of 545 cells/μL, and 60% had recent syphilis within six months prior to the onset of acute hepatitis A. HAV vaccination protected recipients from acute hepatitis A (adjusted odds ratio, 0.03; 95% CI, 0.001 to 0.12), with an overall vaccine effectiveness of 97.4% (Table).