Universal Pneumococcal Vaccine: Towards Protection Against All Serotypes

04 Sep 2026

Tags: Science & Technology   Emerging Tech   Biotechnology

Source: The Hindu

Context: Streptococcus pneumoniae (S. pneumoniae) is a bacterium normally present in the nose and throat and is generally harmless.

• It has 100+ serotypes. When immunity is weakened, it can invade the lungs, brain/spinal cord or bloodstream, causing pneumonia, meningitis and sepsis.
• Existing pneumococcal vaccines protect against only a subset of serotypes, creating a need for a universal vaccine covering all major serotypes.

Why Existing Vaccines Have Limitations

• Pneumococcal vaccines use capsular polysaccharides—sugar molecules specific to individual serotypes—to generate immunity.
• Pneumococcal polysaccharide vaccines (PPVs): contain purified polysaccharides from multiple serotypes; e.g., Pneumovax 23. They provide relatively short-lived protection and work poorly in infants.
• Pneumococcal conjugate vaccines (PCVs): link polysaccharides to a carrier protein, improving the strength and durability of immunity. Examples include PCV10 and PCV13/14, with the number indicating the serotypes targeted.
• A vaccine covering all 100+ serotypes would require incorporating numerous serotype-specific polysaccharides, making it technically difficult and expensive.

Problem of Serotype Replacement

• Elimination of vaccine-targeted serotypes can create ecological space for non-vaccine serotypes to multiply and replace them.
• Some non-vaccine serotypes already possess antibiotic-resistance genes or can acquire them from resistant bacteria.
• This can contribute to the emergence of both vaccine-resistant/non-vaccine serotypes and antibiotic-resistant pneumococci, allowing pneumococcal disease to persist.

New Approach: Protein-Based Universal Vaccine

• British scientists have explored replacing serotype-specific polysaccharides with proteins common across multiple serotypes, combined with reverse vaccinology.
• Reverse vaccinology: identifies potential vaccine targets by analysing a pathogen’s genome, rather than first growing the pathogen and experimentally screening its components.
• The approach was successfully demonstrated during COVID-19 vaccine development, when genomic sequencing enabled scientists to rapidly identify the spike-protein gene as a vaccine target.

Identifying Universal Vaccine Candidates

• The S. pneumoniae genome contains 2,000+ genes, of which around 1,300 are common across serotypes.
• Researchers analysed genomic data from 20,000+ isolates covering nearly 100 serotypes using computational and bioinformatic tools.
• Ideal vaccine proteins were selected based on three criteria: surface accessibility, minimal similarity to human proteins to avoid autoimmune reactions, and ability to generate strong and durable immunity.
• Three candidates were ultimately selected: zinc metalloprotease B (Z), pneumococcal adherence virulence factor A (P), and YfhO-like protein (Y).
• These were combined with immune-response enhancers CpG (synthetic DNA) and chitosan (a polysaccharide polymer) to create the experimental ZPY-CpG-Ch vaccine.

Experimental Results

• In mice challenged with a lethal dose of highly virulent serotype 1, vaccination produced 80–100% survival, compared with complete mortality among unvaccinated mice.
• Its protection was comparable to PCV13 in the experiments.
• Antibodies generated by vaccination were capable of killing pneumococci in laboratory tests and could transfer protection to unvaccinated mice.
• The vaccine provided 100% protection against non-vaccine serotypes 11A and 33F and 50% protection against serotype 8.
• Reduction in bacterial loads in the lungs and blood broadly corresponded with improved survival.

Important Limitation: Transmission Not Prevented

• Despite protecting mice from severe disease, ZPY-CpG-Ch did not reduce pneumococcal bacterial load in the upper respiratory tract.
• Therefore, vaccinated animals could potentially carry and transmit the bacteria despite being protected from disease.
• This distinction is important: a vaccine may provide individual protection without necessarily providing strong population-level protection by blocking transmission.

Significance and Way Forward

• The study also showed activation of certain immune-cell subsets involved in pneumococcal immunity, supporting the vaccine's potential.
• However, ZPY-CpG-Ch cannot yet be considered a universal pneumococcal vaccine because it has been tested against only four serotypes and only in laboratory mice.
• Protection observed in animal models may not necessarily translate directly to humans.
• Nevertheless, targeting conserved proteins shared across serotypes through reverse vaccinology offers a promising pathway towards a vaccine capable of overcoming serotype replacement, limited vaccine coverage and antimicrobial resistance.