Should patients receive 23-valent pneumococcal vaccination more than once?

Streptococcus pneumoniae is the most common cause of community-acquired pneumonia and the second most common cause of bacterial meningitis in the United States. An estimated 40,000 people die annually in the US from pneumococcal infections. Even with antibiotic treatment and intensive care unit support, the mortality of patients with pneumococcal bacteremia approaches 25% to 30%. Because of the importance of this pathogen, it has been the focus of several trials to demonstrate the efficacy of the primary vaccination. To date, 7 meta-analyses have been completed to assess the efficacy of pneumococcal vaccine in adults, with varying results. Most recently, a Cochrane Review (updated in 2005) concluded that "the combined results from randomized studies fail to show that the polysaccharide vaccine is effective in preventing either pneumonia or death." However, they did recognize that the nonrandomized studies have consistently shown that the polysaccharide vaccine is effective in reducing the more specific outcome of invasive pneumococcal disease (bacteremia and meningitis). Multiple studies have used measurement of antibody levels to assess the response of patients to the vaccine and for justification of the need for revaccination. However, measurement of antibody levels to pneumococcal serotypes is difficult, inexact, and is only a surrogate marker for the immune status of a patient, which also relies on the overall function of their immune system. Although pneumococcal vaccine is most highly recommended in patients with chronic disease or immunodeficiency, these patients have a poorer initial response rate and a faster decline in antibody levels than younger, immunocompetent recipients of the vaccine. A study of pneumococcal strains cultured from hospitalized patients demonstrated a duration of protection against pneumococcal infection that was much longer than that predicted by the shorter duration of antibody levels. The vaccine's ability to reduce infection (due to serotypes included in the vaccine) lasted for at least 9 years and overall efficacy for preventing infection caused by the serotypes included in the vaccine was 57%. Revaccination is safe; particularly when performed more than 5 years after the initial vaccination. Injection site reactions are more common and more severe in revaccinated persons (rising from 3% to 15% in the immunocompetent patient). Revaccination, however, does not result in increased rates of hospitalization, and few severe reactions have been reported. No randomized or prospective trials regarding the clinical efficacy of revaccination have been completed. However, when reviewing the studies of antibody response, several summary conclusions can be made. Among those who were nonresponders to the initial vaccination, revaccination (even repeated revaccination) is not effective in stimulating any significant antibody response. Among those who responded to the primary vaccination, revaccination can stimulate a second antibody response-albeit to lower levels and with less duration than after the initial vaccination. Among those who do respond to revaccination, antibody levels can rapidly decline to undetectable levels in a matter of months, and they may or may not retain protection against disease over time. It appears that revaccination recommendations have been based on the safety of the vaccination, concern for patients at risk and reduced antibody levels, rather than on proven clinical utility.