Why Do We Need Another Pneumococcal Vaccine?

Merck recently announced promising results from 2 phase 3 clinical trials on a new 21-valent pneumococcal vaccine. Currently in the US, we have 3 approved pneumococcal vaccines: a 23-valent polysaccharide vaccine, Pneumovax (Merck), and 2 conjugate vaccines—15-valent Vaxneuvance and 20-valent Prevnar 20 (both Pfizer products).

While the first pneumococcal vaccine was developed 112 years ago in South Africa to reduce the incidence of pneumonia in gold mine workers, the first widespread use of a pneumococcal vaccine was in 1977 with a 14-valent polysaccharide vaccine. That shot was replaced in 1983 with the 23- valent Pneumovax, which is still in use today.

Many of us carry pneumococcus in our noses. Presumably, sometimes a strain gets into the blood stream leading sometimes to invasive disease. Only humans can spread pneumococcus (no animal reservoirs). While there are more than 100 pneumococcal strains identified, many do not cause invasive disease and others are rarely seen.

The invasive pneumococcal diseases (IPD) include meningitis, pneumonia with bacteremia, and bacteremia/sepsis. Pneumococcus can also cause noninvasive disease such as pneumonia without bacteremia, sinusitis, and otitis media.

The pneumococcal conjugated vaccines prevent nasal carriage of the bacteria so have a herd protection effect. The polysaccharide Pneumovax vaccine does not impair carriage but is helpful against invasive and noninvasive diseases. Immunity conferred by Pneumovax wanes, particularly in the elderly, and is gone after 5 years. The much longer efficacy of conjugate vaccines comes from broader stimulation of the immune system, including B-cells and T-cells, unlike the polysaccharide vaccines that only affect B-cells.