Is the pneumococcal (Streptococcus pneumoniae) vaccine an mRNA (messenger ribonucleic acid) vaccine?

Pneumococcal Vaccines Are Not mRNA Vaccines

No, the pneumococcal vaccine is not an mRNA vaccine. Pneumococcal vaccines are either polysaccharide vaccines or polysaccharide-protein conjugate vaccines, depending on the specific formulation 1.

Types of Pneumococcal Vaccines

Currently available pneumococcal vaccines fall into two main categories:

1. Pneumococcal Polysaccharide Vaccines (PPSV)

   • Example: PPSV23 (Pneumovax 23)
   • Composition: Contains 23 purified capsular polysaccharide antigens of Streptococcus pneumoniae
   • Mechanism: Polysaccharide antigens induce type-specific antibodies that enhance opsonization, phagocytosis, and killing of pneumococci
   • First licensed in the United States in 1983 1

2. Pneumococcal Conjugate Vaccines (PCV)

   • Examples: PCV13 (Prevnar 13), PCV15 (Vaxneuvance), PCV20 (Prevnar 20)
   • Composition: Contain purified capsular polysaccharides conjugated to a carrier protein
   • Mechanism: Conjugation of polysaccharides to proteins changes the immune response from T-independent to T-dependent, making them more immunogenic
   • PCV13 was licensed in 2011, PCV15 in 2021, and PCV20 most recently 1

Composition and Mechanism

Pneumococcal vaccines work by using pneumococcal capsular polysaccharides as antigens to generate serotype-specific antibodies. These antibodies facilitate serotype-specific clearance of pneumococci through opsonophagocytosis 1.

• PPSV23: Contains 25 μg of each of the 23 capsular polysaccharide antigens dissolved in isotonic saline solution with phenol (0.25%) or thimerosal (0.01%) as preservative and no adjuvant 1

• PCVs: Include purified capsular polysaccharides coupled with a protein carrier (such as CRM197, a nontoxic variant of diphtheria toxin). For example, PCV7 contained approximately 2 μg each of capsular polysaccharide from various serotypes, 20 μg of the carrier protein CRM197, and 0.125 mg of aluminum as an adjuvant 1

Differences from mRNA Vaccines

mRNA vaccines (like some COVID-19 vaccines) use messenger RNA to instruct cells to produce a protein that triggers an immune response. In contrast, pneumococcal vaccines:

1. Directly present polysaccharide antigens to the immune system rather than instructing cells to produce antigens
2. Do not contain any genetic material (mRNA) that enters human cells
3. Have been in use for decades (PPSV since the 1980s, PCVs since the early 2000s)

Clinical Implications

Understanding the type of vaccine is important for clinical decision-making:

• Age considerations: Polysaccharide vaccines (PPSV23) are poorly immunogenic in children under 2 years, while conjugate vaccines (PCVs) are effective even in young children 2
• Immunocompromised patients: Response to pneumococcal vaccination may be diminished in immunocompromised patients 1
• Vaccination schedules: Different recommendations exist for different age groups and risk categories 1

The distinction between pneumococcal vaccines and mRNA vaccines is important for patient education, addressing vaccine hesitancy, and ensuring appropriate expectations regarding immune response and potential side effects.