Pneumonia vaccination

There are two variants of pneumonia vaccination - Pneumococcal polysaccharide vaccine (PPV or PPSV) and Pneumococcal conjugate vaccine (PCV).

There are some key differences between them in terms of effectiveness, number of strains vaccinated against, apart from cost which I summarise below.

• PPV inoculates against 23 strains (serotypes) of Streptococcus pneumoniae, while PCV inoculates against 13 strains.
• PPV is cheaper (£30) than PCV (£70) but PPV is less robust than PCV.
• The immunity due to PPV is also not life long thus requiring revaccination in old age.  This is unlike PCV which provides lifelong immunity.
• Since mucosal immunity is not provoked by PPV, it does not reduce carrier rates and hence does not promote herd immunity. This is unlike PCV which confers mucosal immunity.
• Unlike PCV, PPV is ineffective in children and many older adults. 

A new vaccine [1] is under development that provokes an immune response to 72 strains. This variant is called Liposomal Encapsulation of PolySaccharides (LEPS). This confers herd immunity and does not seem to require a booster dose later in life.

Reference:
[1] Jones, Charles H., Guojian Zhang, Roozbeh Nayerhoda, Marie Beitelshees, Andrew Hill, Pooya Rostami, Yi Li, Bruce A. Davidson, Paul Knight, and Blaine A. Pfeifer. "Comprehensive vaccine design for commensal disease progression." Science advances 3, no. 10 (2017): e1701797.

https://advances.sciencemag.org/content/3/10/e1701797