UNIVERSAL PNEUMOCOCCAL VACCINE MAY TRANSFORM DISEASE PREVENTION

Why in the News ?

Scientists have developed an experimental protein-based pneumococcal vaccine using reverse vaccinology, showing broad protection against multiple Streptococcus pneumoniae serotypes in mice. The research marks an early step towards a universal vaccine against pneumonia, meningitis and other pneumococcal diseases.

Pneumococcal Disease and Need for Universal Vaccine

●     Disease-causing bacterium: Streptococcus pneumoniae normally colonises the nose and throat, but weakened immunity can allow it to cause pneumonia, meningitis and sepsis.

●     Serotype diversity: The bacterium exists in around 100 serotypes, each possessing distinctive capsular polysaccharides that determine the specificity of existing vaccines.

●     Existing vaccines: Pneumococcal conjugate vaccines (PCVs) use capsular polysaccharides linked to carrier proteins, while polysaccharide vaccines such as Pneumovax 23 provide broader but relatively short-lived protection.

●     Serotype replacement: Eliminating vaccine-targeted serotypes can allow non-vaccine serotypes to occupy the ecological niche, potentially reducing long-term vaccine effectiveness.

●     Antibiotic resistance: Non-vaccine serotypes may harbour or acquire antibiotic-resistance genes, increasing the risk of difficult-to-treat pneumococcal infections.

Experimental Results and Remaining Challenges

●     Mouse protection: Vaccinated mice showed 80–100% survival after exposure to a lethal dose of serotype 1, compared with complete mortality among unvaccinated mice.

●     Broad response: The vaccine fully protected mice against serotypes 11A and 33F and provided partial protection against serotype 8, demonstrating cross-serotype potential.

●     Comparable efficacy: Protection against severe disease was broadly comparable to PCV13 in the experimental model.

●     Transmission concern: Despite preventing severe infection, the vaccine did not significantly reduce bacterial presence in the upper respiratory tract, meaning vaccinated animals could potentially continue transmitting bacteria.

●     Preliminary stage: The findings remain preclinical, covering only four serotypes in mice; therefore, effectiveness, safety and durability in humans require extensive further research.

 About Reverse Vaccinology and Vaccine Science:

●     Genome-based approach: Reverse vaccinology begins with the pathogen’s genome to identify proteins that could serve as vaccine targets rather than relying primarily on conventional pathogen cultivation.

●     COVID-19 example: Genome sequencing of SARS-CoV-2 enabled rapid identification of the spike protein, facilitating vaccine development during the pandemic.

●     Protein candidates: Researchers identified three conserved proteins—Zinc metalloprotease B (Z), Pneumococcal adherence virulence factor A (P), and YfhO-like protein (Y).

●     Vaccine formulation: The experimental ZPY-CpG-Ch formulation combined these proteins with CpG synthetic DNA and chitosan, which function as immune-response enhancers.

●     Immune principle: Effective vaccine antigens should ideally be surface-accessible, sufficiently different from human proteins and capable of inducing strong and durable immunity.