The role of vaccination in preventing pneumococcal disease in adults.

Pneumococcal infections, including pneumonia and invasive disease, are major sources of morbidity and mortality worldwide. Prevention of the first acquisition of Streptococcus pneumoniae through the use of vaccines represents an effective method to reduce the burden of the disease in both children and adults. Two vaccines are currently available in adults: a pneumococcal polysaccharide vaccine (PPV23) that includes 23 purified capsular polysaccharide antigens and a pneumococcal protein-conjugate vaccine (PCV13) that includes capsular polysaccharide antigens covalently linked to a non-toxic protein. The PPV23 induces a humoral immune response and since it has been licensed has been the subject of debates and controversies. Numerous studies and meta-analyses have shown that PPV23 protects against invasive pneumococcal disease, although there are conflicting data regarding its efficacy for the prevention of pneumonia. Vaccination with PCV13 stimulates good antibody responses as well as mucosal immunity and suppresses colonization. A conjugate vaccine can be expected to have benefits over a polysaccharide vaccine because of the characteristics of a T-cell-dependent response in terms of affinity, maturation of antibodies with repeated exposure, induction of immunological memory and long-lasting immunity. PCV13 has demonstrated all of these characteristics in children and fundamental differences in adults are not expected. The efficacy in adults is currently being investigated and results will be available soon.