Meningococcal C conjugate vaccine effectiveness before and during an outbreak of invasive meningococcal disease due to Neisseria meningitidis serogroup C/cc11, Tuscany, Italy

• DOI: 10.1016/j.vaccine.2018.06.002
• Publication Date: 2018-06-09T11:48:44Z
• Authors: Patrizio Pezzotti; Alessandro Miglietta; Arianna Neri; Cecilia Fazio; Paola Vacca; Fabio Voller; Giovanni Rezza; Paola Stefanelli
• Keywords: Adult; Male; Adolescent; Meningococcal Vaccines; Neisseria meningitidis, Serogroup C; Meningitis, Meningococcal; Disease Outbreaks; Meningococcal C conjugate vaccine; Young Adult; 03 medical and health sciences; 0302 clinical medicine; Humans; Treatment Failure; Child; Aged; Retrospective Studies; Vaccine effectiveness; Aged, 80 and over; General Immunology and Microbiology; General Veterinary; Public Health, Environmental and Occupational Health; Infant, Newborn; Invasive meningococcal disease; Infant; Outbreak; Middle Aged; 3. Good health; Infectious Diseases; Invasive meningococcal disease; Meningococcal C conjugate vaccine; Outbreak; Vaccine effectiveness; Adolescent; Adult; Aged; Aged, 80 and over; Child; Child, Preschool; Female; Humans; Infant; Infant, Newborn; Italy; Male; Meningitis, Meningococcal; Meningococcal Vaccines; Middle Aged; Neisseria meningitidis, Serogroup C; Retrospective Studies; Treatment Failure; Young Adult; Disease Outbreaks; Italy; Child, Preschool; Molecular Medicine; Female

In Tuscany, Italy, where a universal immunization program with monovalent meningococcal C conjugate vaccine (MCC) was introduced in 2005, an outbreak of invasive meningococcal disease (IMD) due to the hypervirulent strain of Neisseria meningitidis C/cc11 occurred in 2015-2016, leading to an immunization reactive campaign using either the tetravalent (ACWY) meningococcal conjugate or the MCC vaccine. During the outbreak, IMD serogroup C (MenC) cases were also reported among vaccinated individuals. This study aimed to characterize meningococcal C conjugate vaccines (MenC-vaccines) failures and to estimate their effectiveness since the introduction (2005-2016) and during the outbreak (2015-2016).MenC cases and related vaccine-failures were drawn from the National Surveillance System of Invasive Bacterial Disease (IBD) for the period 2006-2016. A retrospective cohort-study, including the Tuscany' population of the birth-cohorts 1994-2014, was carried out. Based on annual reports of vaccination, person-years of MenC-vaccines exposed and unexposed individuals were calculated by calendar-year, birth-cohort, and local health unit. Adjusted (by birth-cohort, local health unit, and calendar-year) risk-ratios (ARR) of MenC invasive disease for vaccinated vs unvaccinated were estimated by the Poisson model. Vaccine-effectiveness (VE) was estimated as: VE = 1-ARR.In the period 2006-2016, 85 MenC-invasive disease cases were reported; 61 (71.8%) from 2015 to 2016. Twelve vaccine failures occurred, all of them during the outbreak. The time-interval from immunization to IMD onset was 20 days in one case, from 9 months to 3 years in six cases, and ≥7 years in five cases. VE was, 100% (95%CI not estimable, p = 0.03) before the outbreak (2006-2014) and 77% (95%CI 36-92, p < 0.01) during the outbreak; VE was 80% (95%CI 54-92, p < 0.01) during the overall period.In Tuscany, MenC-vaccine failures occurred exclusively during the 2015-2016 outbreak. Most of them occurred several years after vaccination. VE during the outbreak-period was rather high supporting an effective protection induced by MenC-vaccines.