Bacterial meningitis is one of the most dangerous types of a disease that causes inflammation of the brain or central nervous system. When left untreated, bacterial meningitis has a fatality rate as high as 70%, and nearly a quarter of patients who survive the infection are left with severe, permanent neurological complications.
The most common cause of bacterial meningitis is pneumococcal bacteria, an infectious organism that can also cause respiratory infections such as pneumonia. Fortunately, vaccines exist that effectively target the most common strains of pneumococcal bacteria. Unfortunately, a new study suggests that those vaccines are ineffective against a different type of pneumococcal bacteria, one that seems to be causing cases of meningitis in an unexpected way.
The study, which was published in The Pediatric Infectious Disease Journal, noted that the use of vaccines has resulted in a greatly decreased rate of pneumonia and bacterial blood infections. However, the rate of bacterial meningitis has not seen a similar decrease and may have, in fact, increased during the same time frame. The study’s authors believe the problem stems from new vaccine-resistant strains of bacteria that have evolved since vaccines have been in broad use.
Hiding from Vaccines
Pneumococcal conjugate vaccines (PCVs) target strains of Streptococcus pneumoniae bacteria that are covered by a protective capsule that prevents the body’s immune system from effectively fighting the bacteria in the bloodstream. New strains of bacteria, however, are covered by a different type of capsule that current vaccines can’t penetrate.
“Widespread use of vaccines resulted in the emergence of a broad diversity of replacement non-PCV type strains,” said Reshmi Mukerji, MPH, and David E. Briles, PhD, of University of Alabama at Birmingham.
The new bacteria also seem to be causing meningitis in an unexpected way. Unlike the PCV strains, which tend to travel to the brain via the bloodstream, the new non-PCV bacteria don’t often cause blood infections, possibly because their capsules are not effective in resisting the blood’s immune system.
Instead, the study’s authors believe that the non-PCV bacteria build colonies in the nose, throat, or ears and then migrate directly to the brain from those locations.
A New Strategy
To fight these new bacteria, the study’s authors say new vaccines will have to be developed. However, the strategy used by current vaccines likely won’t work for the new bacteria because the new strains have nearly 100 different types of capsules, making it virtually impossible for a single vaccine to target all of them.
The best possible alternative is probably a vaccine that is broadly effective against all types of pneumococcal bacteria, regardless of their capsule type. This could be achieved, the authors think, by targeting proteins involved in the processes of capsule formation or colonization.
“Because virtually all cases of pneumococcal meningitis lead to either permanent neurologic sequelae [complications] or death, it would be well worth the effort to develop a new vaccine capable of preventing pneumococcal meningitis regardless of capsular type,” the authors say. “Such a vaccine would need to protect against colonization with most, if not all, pneumococci.”
Pursuing a new approach to vaccine development would require a major shift in research, but it might be the only way to finally stop this deadly disease.