Streptococcus pneumoniae causes pneumonia and invasive disease. The rate of invasive pneumococcal disease (IPD) is five to forty-times higher in HIV-infected patients (39, 40), despite the use of antiretroviral therapy (41), with mortality rates ranging from 0-33% (39-41), and up to 57% in those with bacteraemia in the pre-ART era (42). Risk factors for severe disease include a low CD4+ T cell count, African race, injecting drug use, smoking, chronic disease and alcoholism (43).
There are currently two pneumococcal vaccines available in Australia: one containing capsular polysaccharides of 23 serotypes of pneumococci (PPV23) and the other containing protein-conjugated polysaccharides of 13 serotypes of pneumococci (PCV13).
13-valent protein-conjugated pneumococcal polysaccharide vaccine (PCV13)
Protein-conjugated pneumococcal vaccines are designed to elicit a T cell-dependent B cell response resulting in superior antibody and memory B cell responses. In a previous study in Malawian adolescents and adults, two doses of a protein-conjugated pneumococcal polysaccharide vaccine (PCV7) resulted in a vaccine efficacy of 74% against recurrent IPD caused by vaccine serotypes (44). Multiple serological studies have confirmed significant increases in serum serotype-specific IgG antibody levels and opsonophagocytic antibody activity against pneumococci in HIV positive patients (including those with low CD4+ T cell counts) after a single dose, with further doses providing little advantage for increasing antibody levels (45, 46). A single dose of PCV13 is recommended for all HIV positive patients regardless of CD4+ T cell count, 12 months after PPV23 if this was given first.
23-valent pneumococcal polysaccharide vaccine (PPV23)
There is substantially reduced PPV23 vaccine immunogenicity in HIV patients compared with young healthy controls, particularly among those with low CD4+ T cell counts (47). Numerous observational studies have reported varying clinical effectiveness of PPV23, ranging from 20-79%, against IPD with factors associated with clinical failure including low CD4+ T cell count (<200/mL), African-American race and HIV viral load >100,000 copies/mL (48). Administration of PPV23 at least 12 months after PCV13 is recommended, to increase pneumococcal serotype coverage of antibody responses, with a repeated dose 5 years later.