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Herd protection or herding cats?
  1. Mark van der Linden1,
  2. Cynthia G Whitney2
  1. 1 National Reference Center for Streptococci, Department of Medical Microbiology, University Hospital RWTH Aachen, Aachen, Germany
  2. 2 Centers for Diseases Control and Prevention, Atlanta, Georgia, USA
  1. Correspondence to Dr Mark van der Linden, National Reference Center for Streptococci, Department of Medical Microbiology, University Hospital RWTH Aachen, Aachen 52074, Germany; mlinden{at}

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In this issue of Thorax, Hanquet et al 1 present results of surveillance for invasive pneumococcal disease (IPD) among adults aged 65 years and older in 10 European countries during the 5 years 2011–2015 following introduction of second-generation pneumococcal conjugate vaccines for infants that covered 10 (PCV10) or 13 (PCV13) of the more than 90 pneumococcal serotypes. They also compared the incidence rates to the pre-PCV10/13 year 2009. A total of 56 194 cases of disease are reported. Since the authors are quantifying the effects of PCVs rolled out as part of infant immunisation programmes throughout Europe around 2010, the trends described are entirely indirect, or herd, effects. In other words, the authors describe how well pneumococcal conjugate vaccine programmes are interrupting pneumococcal transmission from children, and therefore, preventing disease in vulnerable older adults. The key questions the authors address are whether herd protection effects differ depending on the vaccine used in childhood immunisation programmes (PCV10 or PCV13) and whether vaccination of the elderly themselves with PCV13 has value, considering the reduction in circulating vaccine-serotype pneumococci and herd protection.

Given the high number of pneumococcal serotypes that have been described, trying to prevent overall disease using vaccines that target a relatively small number of serotypes could end up being like herding cats; disease caused by some serotypes will move in the right direction, and disease caused by others may not. Most countries …

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