Why the recent ACIP recommendations regarding conjugate pneumococcal vaccine in adults may be irrelevant.

The Advisory Committee on Immunization Practices of the US Centers for Disease Control (ACIP) has recently recommended the 13-valent protein-conjugate pneumococcal vaccine (PCV13) for routine use in adults age 18-65 who have immunocompromising conditions as well as in all adults over the age of 65. By comparison to 23-valent pneumococcal polysaccharide vaccine (PPSV23), antibody responses to PCV13 are similar or modestly better one month after vaccination. The implication that PCV13 will provide more persistent immunity has been disproven; 12 months later, recipients of PPSV23 or PCV13 have identical anti-pneumococcal activity. The theoretical concept that a protein-based vaccine will be followed by a booster effect when pure polysaccharide antigens are administered is based on remarkably little evidence. The strongest objection to the current recommendations is that, since PCVs stimulate mucosal antibodies, the widespread use of these PCVs has led to a near-disappearance of vaccine serotypes from the population. This phenomenon has been amply documented for PCV7, and PCV13 is well on its way to doing the same. Thus, as US physicians are convincing their adult patients to receive 2 "pneumonia shots" instead of one, the use of PCV13 in the USA is rapidly becoming irrelevant.