Pneumococcus
Streptococcus pneumoniae has historically been associated with an enormous disease burden. It remains the most common bacterial cause of community-acquired pneumonia and can cause invasive infections with significant morbidity and mortality. Invasive pneumococcal disease (IPD) includes meningitis and pneumococcal pneumonia with concomitant bacteremia or seeding of other sterile sites. It strikes with a bimodal peak, affecting young children and older adults most commonly. The overall incidence of IPD is approximately 43,500 cases annually, with 5,000 deaths, the majority of which occur in older adults. Routine pneumococcus vaccination is recommended for all adults at age 65 to prevent invasive pneumococcus, but coverage in this population is estimated at only 60%.
There are two types of vaccines for S. pneumoniae: the pneumococcal polysaccharide vaccine (PPSV) and the pneumococcal conjugate vaccine (PCV). Antibodies conveying protection from invasive disease are type specific, and the numbering at the end of the vaccine indicates how many capsular subtypes are in the vaccine. The vaccine derived directly from the polysaccharide capsule was the initial design and in 1983 was released as pneumococcal polysaccharide vaccine 23 (PPSV-23). This vaccine has an estimated efficacy of 74% for preventing IPD but no known efficacy for the prevention of pneumococcal pneumonia.
In 2000, a pneumococcal vaccine with the polysaccharides conjugated to a protein was introduced for vaccinating children younger than 2 years (PCV-7). In 2010, the conjugate vaccine was updated to PCV-13. The serotypes covered in PCV-13 account for 44% of disease in individuals aged 65 and older, although PPSV-23 covers 66% of the serotypes of invasive disease in this population. Full implementation of the PCV-7 in children has had a major effect on the epidemiology of IPD in all age groups. When children were vaccinated, all age groups demonstrated an 87 to 92% reduction in pneumococcal disease caused by serotypes in PCV-7. The overall incidence rate of invasive pneumococcal disease in all ages was reduced by 45%, and the incidence of IPD in adults 65 and older was reduced by 37%. Determining the effect on pneumococcal disease since the introduction of PCV-13 in infants is widely anticipated.
The ACIP recently changed its recommendation for routine pneumococcal vaccination in adults aged 65 and older. As a result of the Community-Acquired Pneumonia Immunization Trial in Adults, a large study in the Netherlands involving 85,000 vaccine-naive individuals aged 65 and older who received PCV-13 or placebo, these new recommendations now incorporate PCV-13 universally in all individuals aged 65 and older. Preliminary data released this year showed 75% fewer cases of vaccine type–specific IPD and 45% fewer cases of type-specific community-acquired pneumonia, including nonbacteremic, noninvasive disease. This follows an earlier change in the guidelines from 2012 that recommend PCV-13 to adults under certain immunocompromising or high-risk conditions, including asplenia or having a cerebrospinal fluid leak or cochlear implant.
PCV-13 is now recommended to all vaccine-naive adults when they turn 65, followed by PPSV-23 6 to 12 months later. For those who have already received their age-appropriate dose of PPSV-23 according to the prior guidelines, they can be given PCV-13 at least 1 year later to complete their pneumococcus vaccine series. If one has received PPSV-23 before turning 65, there should be a 1-year interval before PCV-13 is administered, and the follow-up PPSV-23 should be administered no sooner than 5 years after the previous PSPV-23 dose (Figure 1). These intervals are designed to maximize immunogenicity using the different vaccine formulations. Outside of these recommendations, further PPSV-23 doses after age 65 are not recommended.
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Figure 1.
Pneumococcal conjugate vaccine (PCV)-13 schedule for individuals aged 65 and older. The scenarios illustrate the timing for administering PCV-13 based on history of pneumococcal polysaccharide vaccine (PPSV)-23 vaccine.