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Herd immunity drives down invasive pneumococcal disease in adults

Herd immunity generated by the introduction of the 13-valent pneumococcal conjugate vaccine in the United States — first in 2010 for children, then in 2012 for immunocompromised adults, in series with the 23-valent pneumococcal polysaccharide vaccine — has driven down the incidence of invasive pneumococcal disease, or IPD, in adults with and without underlying medical conditions, researchers reported.

In 2014, the CDC’s Advisory Committee on Immunization Practices (ACIP) recommended that all adults aged 65 years or older routinely receive the 13-valent pneumococcal vaccine (Prevnar 13, Pfizer; PCV13), followed by a dose of the 23-valent polysaccharide vaccine (Pneumovax 23, Merck; PPSV23). Recently, however, the ACIP reversed that recommendation, voting not to recommend routine PCV13 vaccination for older adults. The vote followed continued reductions in pneumococcal disease that have been attributed to the indirect effects from pediatric vaccination.

In an editorial related to the new study, Daniel M. Weinberger, PhD, associate professor of epidemiology, and Eugene D. Shapiro, MD, Infectious Disease News Editorial Board member and professor of pediatrics and epidemiology, both from the Yale School of Public Health, noted that although the PPSV23 vaccine is still recommended for adults aged 65 years or older, ACIP suggested “shared decision-making” — leaving the decision up to doctors and patients — to determine if PPSV23 should be preceded by a PCV13 dose among adults who are not immunocompromised. This, Weinberger and Shapiro noted, still leaves the question of how to protect adults from pneumococcal disease.

“Vaccinating children with a conjugate pneumococcal vaccine seems to be the most efficient way to reduce the burden of disease in adults due to vaccine-targeted serotypes,” they wrote. “However, because children are the main reservoir for pneumococci, introducing a new conjugate vaccine in children not only will either reduce or eliminate asymptomatic carriage of the serotypes of pneumococci in the vaccine (and, consequently, disease caused by those serotypes in adults), but it also will result in an increase in the frequency of colonization of healthy vaccinees with serotypes that are not targeted by the vaccine.”

Herd immunity generated by the introduction of the 13-valent pneumococcal conjugate vaccine in the United States — first in 2010 for children, then in 2012 for immunocompromised adults, in series with the 23-valent pneumococcal polysaccharide vaccine — has driven down the incidence of invasive pneumococcal disease, or IPD, in adults with and without underlying medical conditions, researchers reported. Source: Ahmed SS, et al. Clin Infect Dis. 2019;doi:10.1093/cid/ciz739.

Using the Active Bacterial Core surveillance system and National Health Interview Survey, Tamara Pilishvili, PhD, MPH, an epidemiologist in the CDC’s Respiratory Diseases Branch, and colleagues estimated IPD incidence and compared rates in 2013-2014 with rates in 2007-2008 by age and serotype group, which included PCV13, PPSV23-unique or types in neither vaccine (NVT).

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They reported a decline in the incidence of IPD among all adults. Broken down by age group, PCV13-type IPD incidence among adults aged 19 to 64 years declined 57% (95% CI, –68 to –43) in adults with immunocompromising conditions, 57% (95% CI, –62 to –52) in immunocompetent adults with chronic medical conditions and 74% (95% CI, –78 to –70) in adults with neither vaccine indication.

Among adults 65 years or older, PCV13-type IPD incidence declined 68% (95% CI, –76 to –60) in those with immunocompromising conditions, 68% (95%CI, –72 to –63) in immunocompetent adults with chronic medical conditions and 71% (95%CI, –77 to –64) in healthy adults.

Additionally, the researchers observed an increase in PPSV23-unique types among adults aged 19 to 64 years with chronic medical conditions. Among adults with or without PCV13 indications, NVT did not change.

According to the study, non-PCV13 serotypes accounted for nearly 80% of IPD cases from 2013 to 2014.

“Our study evaluated effects of PCV13 against severe pneumococcal infections among adults with chronic medical conditions using data from a large population-based surveillance system,” Pilishvili told Infectious Disease News. “We found that disease incidence among U.S. adults declined after PCV13 introduction in children. We also saw similar reductions in disease caused by vaccine strains among adults with and without indications for vaccine use. This suggests that observed benefits are largely due to herd protection from pediatric PCV13 use rather than direct PCV13 use among adults.” – by Marley Ghizzone

Disclosures: Pilishvili reports no relevant financial disclosures. Please see the study for all other authors’ relevant financial disclosures. Weinberger reports receiving personal consulting fees from Affinivax, GSK and Pfizer; funding from NIH/NIAID through a grant to Yale; and research funding from Pfizer through a grant to Yale. Shapiro reports receiving consultancy honorarium from Sanofi, funding from NIH/NIAID/NCATS through a grant to his institution, and payments from Grand Rounds, outside the submitted work.