Novel pneumococcal serotypes 6C and 6D: anomaly or harbinger

Area of Science:

• Microbiology
• Immunology
• Vaccinology

Background:

• The 7-valent pneumococcal protein conjugate (PCV7) vaccine significantly decreased invasive pneumococcal disease (IPD) by targeting specific Streptococcus pneumoniae serotypes.
• Serotype replacement, where non-vaccine serotypes increase after vaccination, was anticipated, but misidentification of serotypes presented an unexpected challenge.

Purpose of the Study:

• To describe the emergence and impact of newly recognized pneumococcal serotypes 6C and 6D.
• To evaluate the effectiveness of PCV7 and the potential role of PCV13 against these emergent serotypes.

Main Methods:

• Review of clinical data and serotyping results during the PCV7 vaccination era.
• Analysis of vaccine cross-protection based on serotype characteristics.

Main Results:

• Serotype 6C infections expanded during the PCV7 era, while serotype 6D caused occasional infections.
• PCV7 provided cross-protection against serotype 6A but not against the newly identified serotype 6C.
• Serotype 6D was previously mistyped as 6B, and serotype 6C was likely mistyped as 6A.

Conclusions:

• Unrecognized or misidentified serotypes can significantly impact the efficacy of serotype-specific vaccines.
• The 13-valent pneumococcal protein conjugate (PCV13) vaccine, including serotype 6A, may offer protection against IPD caused by serotypes 6C and 6D.
• Continuous surveillance and accurate serotyping are crucial for monitoring vaccine effectiveness and addressing evolving pathogen dynamics.