Background:  The protective effect of administration of pneumococcal polysaccharide vaccine (PV) to HIV-infected subjects has ranged from 0 to 80%. The incidence of pneumococcal disease has decreased in the HAART era, and it has been hypothesized that HAART improves humoral responses to polysaccharide antigens compared to non-HAART patients. The objective of this study is to compare the rate of vaccine failures among HIV⁺ and HIV^- veterans enrolled in the feasibility phase of the Veterans Aging Cohort Study (VACS 5).

Methods:  VACS 5 is a multisite cohort study with full access to electronic medical records. Of 1851 patients enrolled between September 1, 2001 and March 31, 2002 at 5 VA HIV and General Medicine clinics, 883 had documented pneumococcal vaccine dates (604 HIV⁺, 279 HIV^-). Mean age was 59±10 and 49±9 for HIV^- and HIV⁺, respectively (p <0.01); African Americans represented 42% and 56% of the HIV^- and HIV⁺ vaccinated groups, respectively (p <0.01). Any patient with an ICD9 discharge diagnosis of pneumonia (non-PCP), or pneumococcal pneumonia, bacteremia, meningitis, or sepsis within 1 year after vaccination was considered a vaccine failure. Groups were also categorized based on the presence of other risk factors for pneumococcal disease. Bivariate and univariate analyses including incidence rates and rate ratios were performed using Stata version 8.1.

Results:  There was 1 vaccine failure among 279 HIV^- and 23 among 604 HIV⁺ veterans (0.36% vs 3.80%, respectively, p <0.01) with an incidence rate ratio of 9.35 (p <0.05) for HIV⁺. The increased incidence among HIV⁺ was observed among subgroups associated with increased susceptibility for pneumococcal disease with IRR of 4.1 for HIV⁺ African Americans, 5.3 for HIV⁺ smokers, 7.1 for HIV⁺ binge drinkers, 1.5 for HIV⁺ diabetics, and 3.8 for HIV⁺ with COPD when compared to their HIV^- counterparts; however, it did not reach statistical significance for any of those groups, likely due to the smaller sample size.

Conclusions:  The protective effect of PV among HIV⁺ veterans is decreased when compared with HIV^- controls. The trend to increased risk for vaccine failure was also present when specific groups with increased risk for pneumococcal disease were examined. The increased susceptibility of HIV-infected patients to pneumococcal disease continues to be apparent among vaccinated patients when compared to vaccinated controls.

Keywords: Pneumococcal vaccine; Pneumococci; Pneumococcal pneumonia