Seasonal influenza vaccination uptake in Quebec, Canada, 2 years after the influenza A(H1N1) pandemic.

BACKGROUND: A decrease in seasonal influenza vaccine uptake was observed after the influenza A(H1N1) pandemic in 2009. The goal of our study was to assess seasonal influenza vaccine uptake in 2011-2012, 2 years after the influenza A(H1N1) pandemic mass immunization campaign and to identify the main reasons for having or not having received the vaccine. METHODS: A telephone survey using random-digit dialing methodology was conducted. Case-weights were assigned to adjust for disproportionate sampling and for nonresponse bias. Descriptive statistics were generated for all variables. RESULTS: Seasonal influenza vaccine uptake was 57% among adults aged ≥60 years, 35% among adults with chronic medical conditions, and 44% among health care workers. The main reasons given for having been vaccinated were to be protected from influenza and a high perceived susceptibility to influenza, whereas low perceived susceptibility to influenza and low perceived severity of influenza were the main reasons for not having been vaccinated. CONCLUSIONS: An increase in seasonal influenza vaccine uptake was observed 2 years after the influenza A(H1N1) pandemic. However, vaccine coverage is still below the target level of 80%. More efforts are needed to develop effective strategies to increase seasonal influenza vaccine uptake.

Impact of 2+1 pneumococcal conjugate vaccine program in the province of Quebec, Canada.

BACKGROUND: Quebec was the first jurisdiction in the world to recommend a 3-dose (2+1) pneumococcal conjugate vaccine (PCV) schedule. The program was implemented in December 2004 with a catch-up for children <5 years. PCV-7 was first used and replaced, respectively, by PCV-10 in 2009 and by PCV-13 in 2011. METHODS: Cases of invasive pneumococcal disease (IPD) notified to public health authorities and isolates submitted to the provincial reference laboratory during the period 2000-2011 were analyzed. RESULTS: IPD incidence in children <5 years was 67/100,000 in 2001-2004, and decreased to 32/100,000 in 2007-2009 following PCV-7 implementation (p<0.01). A further decrease to 24/100,000 was observed in 2010-2011 following PCV-10 introduction (p<0.01). PCV-7 serotypes represented 82% of the total IPD cases in 2000-2004 and elimination was achieved in 2011. Main emerging serotypes were 19A and 7F. Children exposed to the PCV-10 experienced lower IPD rates and all serotypes contributed to the decline, mainly 7F and 19A. In adults, a decrease of low magnitude was observed in 2005-2006 but rates in 2007-2009 were higher than in the prevaccination period. CONCLUSIONS: A 3-dose PCV schedule with high uptake is highly effective and should be recommended worldwide. Serotype replacement eroded benefits especially in adults. PCV-10 introduction had an effect and the impact of PCV-13 use remains to be evaluated.

Largest measles epidemic in North America in a decade--Quebec, Canada, 2011: contribution of susceptibility, serendipity, and superspreading events.

BACKGROUND: The largest measles epidemic in North America in the last decade, occurred in 2011 in Quebec, Canada, where rates of 1- and 2-dose vaccine coverage among children 3 years of age were 95%-97% and 90%, respectively, with 3%-5% unvaccinated. METHODS: Case patients identified through passive surveillance and outbreak investigation were contacted to determine clinical course, vaccination status, and possible source of infection. RESULTS: There were 21 measles importations and 725 cases. A superspreading event triggered by 1 importation resulted in sustained transmission and 678 cases. The overall incidence was 9.1 per 100,000; the highest incidence was in adolescents 12-17 years old (75.6 per 100,000), who comprised 56% of case patients. Among adolescents, 22% had received 2 vaccine doses. Outbreak investigation showed this proportion to have been an underestimate; active case finding identified 130% more cases among 2-dose recipients. Two-dose recipients had milder illness and a significantly lower risk of hospitalization than those who were unvaccinated or single-dose recipients. CONCLUSIONS: A chance superspreading event revealed an overall level of immunity barely above the elimination threshold when unexpected vulnerability in 2-dose recipients was taken into account. Unvaccinated individuals remain the immunization priority, but a better understanding of susceptibility in 2-dose recipients is needed to define effective interventions if elimination is to be achieved.

The changing epidemiology of meningococcal disease in Quebec, Canada, 1991-2011: potential implications of emergence of new strains.

BACKGROUND: In order to inform meningococcal disease prevention strategies, we analysed the epidemiology of invasive meningococcal disease (IMD) in the province of Quebec, Canada, 10 years before and 10 years after the introduction of serogroup C conjugate vaccination. METHODOLOGY: IMD cases reported to the provincial notifiable disease registry in 1991-2011 and isolates submitted for laboratory surveillance in 1997-2011 were analysed. Serogrouping, PCR testing and assignment of isolates to sequence types (ST) by using multilocus sequence typing (MLST) were performed. RESULTS: Yearly overall IMD incidence rates ranged from 2.2-2.3/100,000 in 1991-1992 to 0.49/100,000 in 1999-2000, increasing to 1.04/100,000 in 2011. Among the 945 IMD cases identified by laboratory surveillance in 1997-2011, 68%, 20%, 8%, and 3% were due to serogroups B, C, Y, and W135, respectively. Serogroup C IMD almost disappeared following the implementation of universal childhood immunization with monovalent C conjugate vaccines in 2002. Serogroup B has been responsible for 88% of all IMD cases and 61% of all IMD deaths over the last 3 years. The number and proportion of ST-269 clonal complex has been steadily increasing among the identified clonal complexes of serogroup B IMD since its first identification in 2003, representing 65% of serogroup B IMD in 2011. This clonal complex was first introduced in adolescent and young adults, then spread to other age groups. CONCLUSION: Important changes in the epidemiology of IMD have been observed in Quebec during the last two decades. Serogroup C has been virtually eliminated. In recent years, most cases have been caused by the serogroup B ST-269 clonal complex. Although overall burden of IMD is low, the use of a vaccine with potential broad-spectrum coverage could further reduce the burden of disease. Acceptability, feasibility and cost-effectiveness studies coupled with ongoing clinical and molecular surveillance are necessary in guiding public policy decisions.

Long-lasting measles outbreak affecting several unrelated networks of unvaccinated persons.

Despite a population immunity level estimated at approximately 95%, an outbreak of measles responsible for 94 cases occurred in Quebec, Canada. Unlike previous outbreaks in which most unvaccinated children belonged to a single community, this outbreak had cases coming from several unrelated networks of unvaccinated persons dispersed in the population. No epidemiological link was found for about one-third of laboratory-confirmed cases. This outbreak demonstrated that minimal changes in the level of aggregation of unvaccinated individuals can lead to sustained transmission in highly vaccinated populations. Mathematical work is needed regarding the level of aggregation of unvaccinated individuals that would jeopardize elimination.