title: How many individuals with asthma need to be vaccinated to prevent one case of invasive pneumococcal disease?
abstract: BACKGROUND
  The American Advisory Committee on Immunization Practices recommended the inclusion of adults with asthma in the high-risk category for pneumococcal vaccination based on a twofold increase in risk of invasive pneumococcal disease (IPD).
  
  
  OBJECTIVE
  To determine whether, among individuals with asthma, the number needed to vaccinate (NNV) using pneumococcal conjugate vaccine (PCV)-13 or 23-valent pneumococcal polysaccharide vaccine (PPV-23) warrants its addition to the high-risk category for pneumococcal vaccination in Canada.
  
  
  METHODS
  Using IPD incidence (per 10,000 individuals) figures from published articles (4.2 in high-risk asthmatics, 2.3 in low-risk asthmatics and 1.2 in healthy individuals), the NNV to prevent one case of IPD in asthmatics five to 17 years of age and 18 to 50 years of age was calculated, factoring in the proportion of pneumococcal serotypes included in vaccines (based on data from Quebec) and accounting for the possibility of waning vaccine efficacy (VE) using four scenarios.
  
  
  RESULTS
  Assuming a VE of 65% for PCV-13 in asthmatics, the NNV would be 704 to 820 in low-risk and 386 to 449 in high-risk children; and 355 to 1532 in low-risk and 195 to 839 in high-risk adults (range depends on waning scenario). Assuming a VE of 65% for PPV-23 in asthmatics, the NNV would be 581 to 677 in low-risk and 318 to 371 in high-risk children; and 246 to 1059 in low-risk and 135 to 580 in high-risk adults.
  
  
  CONCLUSIONS
  The NNV with both PCV-13 and PPV-23 in asthmatic children and adults is comparable with that of other high-risk conditions such as age ≥65 years. Therefore, the addition of asthma to the list of high-risk conditions for pneumococcal vaccination is warranted.
authors.affiliation: Department of Medical Microbiology and Infectious Diseases;
authors.forename: Julie M
authors.initials: JM
authors.lastname: Okapuu
authors.affiliation: Department of Pediatrics, The Montreal Children's Hospital, McGill University Health Centre, Montreal;
authors.forename: Estelle
authors.initials: E
authors.lastname: Chétrit
authors.affiliation: Laboratoire de santé publique du Québec, Sainte-Anne-de Bellevue; ; Institut national de santé publique du Québec;
authors.forename: Brigitte
authors.initials: B
authors.lastname: Lefebvre
authors.affiliation: Department of Medical Microbiology and Infectious Diseases; ; Department of Pediatrics, The Montreal Children's Hospital, McGill University Health Centre, Montreal; ; Institut national de santé publique du Québec; ; Department of Epidemiology, Biostatistics and Occupational Health, McGill University, Montreal, Quebec.
authors.forename: Caroline
authors.initials: C
authors.lastname: Quach
keywords: Asthma; Pneumococcal; Vaccine