A Prospective Study of Anti-capsular Antibody Responses to Pneumococcal Vaccination among HIV-infected Persons: Emphasis on Impact of Highly Active Anti-Retroviral Therapy

A 4-year prospective longitudinal follow-up study was conducted to assess the immunogenicity of 23-valent pneumococcal polysaccharide vaccine (PPV) among 305 HIV-1 infected individuals who received PPV and HAART between June 2000 and June 2004. 89 randomly selected vaccinees were stratified into 3 groups based on their CD4 counts at baseline: Group 1 with CD4 counts less than 100 cells/µl; Group 2 with CD4 counts between 100 and 350 cells/µl; and Group 3 with CD4 counts higher than 350 cells/µl. Antibody responses to 3 capsular antigens (14, 19F, and 23F) were performed using home-made ELISA. Changes in these parameters from baseline to week 4, and every 6 months thereafter were determined and compared using Student’s t-test. Rates of response to vaccination in different groups of vaccinees were compared using χ2 test. Vaccinees with more than 2-fold increase in antibody responses were defined as vaccine responders. We found that immunization did not cause any significant changes in CD4 counts or plasma HIV-RNA load between vaccinees of different groups. For type 14, both the percentage of responders (27% v.s. 57% v.s. 54%) and the geometric mean fold-rise of reactive antibody (1.38 v.s. 2.89 v.s. 3.05) were significantly lower for Group 1 compared with Groups 2 and 3. The duration of antibody responses in responders was similar between groups. Among the 24 responders who had been followed for more than 3 years, more than 75% of them remained seropositive for type 14 irrespective of their baseline CD4 counts. Our findings suggest that antibody responses to 23-valent PPV are poorer in HIV-infected vaccinees with baseline CD4 counts less than 100 cells/µl compared with those with baseline CD4 counts higher than 100 cells/µl. The responses may last for more than 3 years in 75% of the vaccine responders who continue to receive HAART regardless of baseline CD4 + counts. Patients with HIV infection are at higher risk for invasive infections due to Streptococcus pneumoniae as compared with those without HIV infection. Rates of invasive pneumococcal infections among AIDS patients may be as high as 100-fold greater than in HIV-seronegative controls [1]. In the era of increasing rates of antimicrobial resistance among isolates of S. pneumoniae worldwide as well as an increased risk for developing invasive pneumococcal infections among HIV-infected patients, the US Centers for Disease Control and Prevention (CDC) has strongly recommended that pneumococcal vaccination be given to patients with HIV infection who are aged ≥2 years [2] and a CD4+ count ≥200 cells/µl [3]. In addition, revaccination is recommended when the CD4+ count increases to ≥200 cells/µl in patients with an initial CD4+ count of