How do we deal with vaccination for a disease caused by a gram-positive bacterium, such as Streptococcus pneumoniae, with over 90 polysaccharide capsule antigenic types?

From the Guidelines

The most effective way to deal with vaccination against Streptococcus pneumoniae, which has over 90 polysaccharide capsule antigenic types, is to use pneumococcal conjugate vaccines (PCVs) that target the most common disease-causing serotypes, specifically the 21-valent pneumococcal conjugate vaccine (PCV21) which includes serotypes that cause the majority of invasive disease, as recommended by the Advisory Committee on Immunization Practices (ACIP) in 2024 1.

The current approach involves administering PCV21 to adults, which provides coverage against 21 serotypes, including serotype 15B, based on prespecified criteria for the proportion of participants with fourfold or more rise in OPA responses. This strategy works because although S. pneumoniae has numerous serotypes, approximately 20-30 serotypes cause the majority of invasive disease.

Some key points to consider:

• The conjugate vaccines enhance immunogenicity by linking polysaccharide antigens to protein carriers, making them effective even in young children whose immune systems respond poorly to pure polysaccharide vaccines.
• The 21-valent pneumococcal conjugate vaccine (PCV21) is approved for the prevention of invasive pneumococcal disease caused by serotype 15B.
• PCV21 contains serotype 20A, in addition to the other 20 serotypes included in the vaccine.

Overall, the use of PCV21 provides broad coverage against Streptococcus pneumoniae, and is a recommended vaccine for adults, particularly those 65 and older or 19-64 with risk factors, as it has been shown to be effective in preventing invasive pneumococcal disease despite the bacterium's antigenic diversity 1.

From the FDA Drug Label

PNEUMOVAX 23 (Pneumococcal Vaccine Polyvalent) is a sterile, liquid vaccine consisting of a mixture of purified capsular polysaccharides from Streptococcus pneumoniae types (1,2,3,4,5, 6B, 7F, 8, 9N, 9V, 10A, 11A, 12F, 14, 15B, 17F, 18C, 19F, 19A, 20, 22F, 23F, and 33F).

The likeliest cause of this disease is a gram-positive bacterium, such as Streptococcus pneumoniae, with over 90 polysaccharide capsule antigenic types.

• The vaccines are composed of up to twenty three of the most prevalent capsule types 2.
• PNEUMOVAX 23 is a vaccine that contains 23 serotypes of pneumococcal capsular polysaccharides.
• Prevnar 20 is another vaccine that contains 20 serotypes of pneumococcal capsular polysaccharides conjugated to a carrier protein 3. The vaccines do not include all of the various capsule types, but rather a selection of the most prevalent ones.

From the Research

Dealing with Vaccination for Streptococcus pneumoniae

The likeliest cause of the disease described is a gram-positive bacterium, such as Streptococcus pneumoniae, which has over 90 polysaccharide capsule antigenic types. To deal with vaccination for this disease, the following points are relevant:

• The vaccines are composed of up to twenty-three of the most prevalent capsule types, as seen in the pneumococcal conjugate vaccine (PCV13) and the polysaccharide vaccine (PPSV23) 4, 5, 6.
• These vaccines elicit distinct humoral responses, with PCV13 inducing a broader and more durable antibody response compared to PPSV23 5.
• The use of conjugate vaccines, such as PCV13, has been shown to reduce the incidence of invasive pneumococcal disease and nasopharyngeal carriage, and to induce herd immunity 4, 5.
• However, the replacement of serotypes eradicated by the vaccine with non-vaccine serotypes is a concern, and may threaten the success of vaccine use 4, 7.

Vaccine Composition

The composition of the vaccines is crucial in determining their effectiveness. The options for vaccine composition are:

• The vaccines are composed of all of the various capsule types: This is not currently the case, as there are over 90 polysaccharide capsule antigenic types, and the vaccines only contain up to 23 of the most prevalent types.
• The vaccines are composed of up to twenty-three of the most prevalent capsule types: This is the current approach, with vaccines such as PCV13 and PPSV23 containing up to 23 capsule types.
• The vaccines are changed from year to year to match the expected antigenic type for the upcoming season: This is not the case for pneumococcal vaccines, as the antigenic types are not as predictable as those for influenza.
• The vaccines are composed of non-capsular fibrillar proteins to which antibody responses are protective: This is not the current approach, as the vaccines are focused on the capsular polysaccharides.
• A live, attenuated vaccine strain is used so that an immune response against the full repertoire of protective antigens can be elicited: This is not the current approach, as the vaccines are not live, attenuated strains.

The correct answer is b. the vaccines are composed of up to twenty three of the most prevalent capsule types 4, 5, 6.