Level 2: Mid-level evidence
To date, the efficacy of the pneumococcal polysaccharide vaccine (Pneumovax) has been found to be inconsistent in systematic reviews. Now, the first systematic review to explicitly consider trial quality suggests that the vaccine is ineffective (CMAJ. 2009;180:48-58, accessed March 11, 2009). Included in the review were 22 randomized or quasi-randomized trials of pneumococcal polysaccharide vaccine with 101,507 adults. The vaccine was associated with a reduced risk for presumptive pneumococcal pneumonia and for all-cause pneumonia in comprehensive meta-analyses. However, these meta-analyses were limited by substantial heterogeneity, and there were no significant differences in analyses limited to higher-quality trials (i.e., trials with blinding and allocation concealment). The authors concluded that “pneumococcal vaccination does not appear to be effective in preventing pneumonia, even in populations for whom the vaccine is currently recommended.”

A number of organizations, including the CDC’s Advisory Committee on Immunization Practices (ACIP), the American Academy of Family Physicians (AAFP), the American College of Physicians (ACP), and the American College of Obstetricians and Gynecologists (ACOG), currently recommend pneumococcal polysaccharide vaccination for persons older than 65 years, smokers, and residents of long-term-care facilities. The vaccine is also indicated for persons with any of the following conditions: chronic liver, cardiovascular, or lung disease (including asthma); diabetes mellitus; chronic alcoholism; chronic renal failure or nephrotic syndrome; functional or anatomic asplenia; impaired immune function; cochlear implants; or cerebrospinal fluid leaks. The U.S. Preventive Services Task Force has stopped updating its recommendations for immunizations for adults.

However, all pneumococcal vaccines may not be ineffective. Recently published epidemiologic data showed that the incidence of pneumococcal meningitis in the United States decreased significantly since the introduction of the 7-valent pneumococcal conjugate (Prevnar, PCV7) vaccine (N Engl J Med. 2009;360:244-256, accessed March 11, 2009). Annual incidence per 100,000 population fell from 1.13 in 1998-1999 to 0.79 in 2004-2005 for all serotypes in all ages. Over the same period, incidence of pneumococcal meningitis per 100,000 persons fell among children younger than 2 years (from 10.16 to 3.66 cases) and among adults 65 years or older (from 1.90 to 0.87 cases). Furthermore, a recent CDC analysis found a significant decrease in hospitalizations for pneumonia in children younger than 2 years when researchers compared the time periods before and after the introduction of the PCV7 in 2000 (MMWR Morb Mortal Wkly Rep. 2009;58:1-4, accessed March 11, 2009).

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The ACIP, AAP, and AAFP currently recommend a four-dose PCV7 series for all children younger than 23 months. Healthy children aged 24-59 months who have not received the full PCV7 series should get one dose of PCV7. Children aged 24-59 months who are immunocompromised or at high risk of HIV infection, sickle cell anemia, asplenia, chronic illness, or other invasive illness should receive one additional dose of PCV7 if previously immunized with at least three doses. Eligible children aged 12-59 months who have received fewer than three doses should be given two additional doses at least eight weeks apart.