Thomas Fekete, MD, FCCP, Section Chief, Infectious Diseases; Professor, Medicine; Associate Professor, Microbiology and Immunology; School of Medicine, Temple University
Many medications that are essential for the health of children were first developed to treat adults and only later tested on children. Several factors probably contributed to this: for example, adults tend to have more illnesses than children, which may provide more testing opportunities. Additionally, many researchers feel that it is ethically preferable to try new medicines for children only when they already have a record of safety in adults. For vaccinations, the process is often reversed because adults are not prone to acquiring certain infections (e.g., Haemophilus influenzae type b [Hib]) or because vaccinating children is likely to have benefits both in childhood and later in adulthood (e.g., the varicella vaccine protects children from varicella disease, which in turn protects them from varicella zoster, or shingles, as adults).
The history of pneumococcal vaccine is different and points out some of the different challenges of preventing disease in adults versus children. A well-tolerated and safe pneumococcal polysaccharide vaccine [PPSV] for adults has been around for three decades. This vaccine was not useful in very young children because they have inadequate production of antibodies to polysaccharide antigens and hence are unprotected when given PPSV. (See this video of vaccine developer John Robbins, MD, discussing why this is so.) However once the success of protein-conjugated polysaccharide vaccines was appreciated, a number of them were developed for young children. There are three successful conjugate vaccines for children that have not been used, or widely used, in adults: Hib, meningococcal, and pneumococcal. Hib vaccine is not needed for adults because of the negligible risk of this infection in adults. Conjugate meningococcal vaccine is standard for children and can also be used for adults who are at unusually high risk of meningococcal disease because of medical condition or travel to a part of world where meningococcal disease occurs in epidemics. Now, as of December 2011, the US FDA has approved a 13-valent pneumococcal conjugate vaccine [PCV-13] for use in adults.
PCV-13 is different from PPSV in a number of ways. PCV-13 contains 13 pneumococcal antigens, each of which is attached to a protein, as compared to PPSV with its 23 unattached polysaccharide antigens. Although PCV-13 was designed to prevent infection by the most severe and common strains of pneumococci found in children, it has reasonable activity for strains causing adult infections. The 23-valent adult vaccine licensed in 1983 has been shown to stimulate the formation of antibodies to S. pneumoniae and to prevent pneumococcal pneumonia. Newer studies in adults have shown that the 13-valent conjugate vaccine elicits comparable levels of antibodies (albeit to a smaller number of pneumococcal strains). In light of this finding, the FDA has licensed the use of conjugate vaccine for adults.
How does this change practice? It is too early to say since we lack detailed clinical information on the practical differences between the two pneumococcal vaccines. The limited data available could be used to support either PCV-13 or PPSV for adults since each has theoretical advantages and disadvantages. The CDC’s Advisory Committee on Immunization Practices, which is staffed with experts in vaccine use, will offer recommendations for adult pneumococcal immunization. Such recommendations may not be forthcoming immediately since the experts may need information not yet available. (The most recent guidelines for adult pneumococcal vaccination were dated September 2010, before PCV-13 was approved for adults.)
In spite of the unclear picture of how the conjugate pneumococcal vaccine will be used in adults, there is good news to be found in the present situation. Use of the conjugate pneumococcal vaccine in children has already reduced the rate of serious pneumococcal infection in both children and adults. The reduction of serious pneumococcal disease in children might not be so surprising since they are directly protected after receiving the vaccine. But one of the added benefits of conjugate vaccines in children is the longer term suppression of colonization by potentially dangerous bacteria. These bacteria may never cause disease in the person who is colonized, but they may be transferred to other people (children or adults) where they might cause serious problems. Delayed or suppressed colonization of children may be limiting spread of the vaccine serotypes in the adult population.
It is also worthwhile to consider that other health measures can have lasting impact on infections. While cigarette smoking is a well-known cause of heart disease and cancer, it is also responsible for significant lung disease, including bacterial pneumonia. Independent of vaccination, an adult who quits smoking can reduce his or her risk of serious pneumococcal infection by 75% within years of smoking cessation. This prevention measure is clearly not relevant in children receiving PCV-13 at age 2 or younger.
We’ll be watching for ACIP to make a recommendation on PCV13 in 2012 meetings in February, June, or October. Following that, any recommendations would be approved by the CDC and HHS and published in the Morbidity and Mortality Weekly Report.
Sources and Recommended Reading
Brown M. FDA committee votes to broaden PCV13 indications to adults 50 and older. AAFP News Now. http://www.aafp.org/online/en/home/publications/news/news-now/health-of-the-public/20111202prevnar50plus.html
Pilishvili T, Lexau C, Farley MM, et al. Sustained reductions in invasive pneumococcal disease in the era of conjugate vaccine. J Infect Dis 2010;201:32–41. http://jid.oxfordjournals.org/content/201/1/32.full.pdf+html?sid=443796ad-d47e-4c38-bdf7-5ddd42c0728b
Splete H. ACIP considers recommending PCV13 for adults. Internal Medicine News. http://www.internalmedicinenews.com/news/infectious-diseases/single-article/acip-considers-recommending-pcv13-for-adults/3593bc5535.html