title: Vaccine Effectiveness of Polysaccharide Vaccines Against Clinical Meningitis - Niamey, Niger, June 2015.
abstract: BACKGROUND
  In 2015, a large outbreak of serogroup C meningococcal meningitis hit Niamey, Niger, in response to which a vaccination campaign was conducted late April. Using a case-control study we measured the vaccine effectiveness (VE) of tri - (ACW) and quadrivalent (ACYW) polysaccharide meningococcal vaccines against clinical meningitis among 2-15 year olds in Niamey II district between April 28th and June 30th 2015.
  
  
  METHODS
  We selected all clinical cases registered in health centers and conducted a household- vaccination coverage cluster survey (control group).  We ascertained vaccination from children/parent reports. Using odds of vaccination among controls and cases, we computed VE as 1-(Odds Ratio). To compute VE by day since vaccination, we simulated a density case control design randomly attributing recruitment dates to controls based on case dates of onset (3 controls per case). We calculated the number of days between vaccination and the date of onset/recruitment and computed VE by number of days since vaccination using a cubic-spline model. We repeated this simulated analysis 500 times and calculated the mean VE and the mean lower and upper bound of the 95% confidence interval (CI).
  
  
  RESULTS
  Among 523 cases and 1800 controls, 57% and 92% were vaccinated respectively. Overall, VE at more than 10 days following vaccination was 84% (95%CI: 75-89) and 97% (94-99) for the tri- and quadrivalent vaccines respectively. VE at days 5 and 10 after trivalent vaccination was 84% (95% CI: 74-91) and 89% (95% CI: 83-93) respectively. It was 88% (95% CI: 75-94) and 95.8% (95% CI: 92 -98) respectively for the quadrivalent vaccine.
  
  
  CONCLUSIONS
  Results suggest a high VE of the polysaccharide vaccines against clinical meningitis, an outcome of low specificity, and a rapid protection after vaccination. We identified no potential biases leading to VE overestimation. Measuring VE and rapidity of protection against laboratory confirmed meningococcal meningitis is needed.
authors.affiliation: EpiConcept, Paris, France.
authors.forename: Marc
authors.initials: M
authors.lastname: Rondy
authors.affiliation: Niamey II Health District, Ministry of Health, Niamey, Niger.
authors.forename: Djibo
authors.initials: D
authors.lastname: Issifou
authors.affiliation: Division of Surveillance and Epidemiological Response (DSRE), Ministry of Health, Niamey, Niger.
authors.forename: Alkassoum S
authors.initials: AS
authors.lastname: Ibrahim
authors.affiliation: Division of Surveillance and Epidemiological Response (DSRE), Ministry of Health, Niamey, Niger.
authors.forename: Zaneidou
authors.initials: Z
authors.lastname: Maman
authors.affiliation: Division of Surveillance and Epidemiological Response (DSRE), Ministry of Health, Niamey, Niger.
authors.forename: Goumbi
authors.initials: G
authors.lastname: Kadade
authors.affiliation: World Health Organization, Geneva, Switzerland.
authors.forename: Hamidou
authors.initials: H
authors.lastname: Omou
authors.affiliation: Centre de Recherche Médicale et Sanitaire (CERMES), Ministry of Health, Niamey, Niger.
authors.forename: Sidikou
authors.initials: S
authors.lastname: Fati
authors.affiliation: EpiConcept, Paris, France.
authors.forename: Esther
authors.initials: E
authors.lastname: Kissling
authors.affiliation: Meningitis and Vaccine Preventable Diseases Branch, Centers for Disease Control and Prevention, Atlanta, Georgia, USA.
authors.forename: Sarah
authors.initials: S
authors.lastname: Meyer
authors.affiliation: World Health Organization.
authors.forename: Olivier
authors.initials: O
authors.lastname: Ronveaux