The largest measles epidemic in North America in a decade--Quebec, Canada, 2011: Contribution of susceptibility, serendipity and super-spreading events on elimination.
ABSTRACT Introduction. We describe the largest measles epidemic in North America in the last decade occurring in the population of Quebec, Canada in 2011 where one- and two-dose vaccine coverage among children 3years of age were 95-97% and 90%, respectively, with 3-5% unvaccinated.Methods. Cases identified through passive surveillance and outbreak investigation were contacted to describe clinical course, vaccination status and possible source of infection.Results. There were 21 measles importations and 725 cases. A super-spreading event triggered by one importation resulted in sustained transmission and 678 cases. The incidence per 100,000 was 9.1, highest in adolescents 12-17years old (75.6) comprising 56% of cases. Among adolescent cases, 22% had received two vaccine doses. Outbreak investigation showed this proportion to have been an under-estimate: active case-finding identified 130% more cases among two-dose recipients. Two-dose recipients had milder illness and significantly lower risk of hospitalization compared to unvaccinated or single-dose cases.Conclusion. A chance super-spreading event revealed an overall level of immunity barely above the elimination threshold when taking into account unexpected vulnerability in two-dose recipients. Unvaccinated individuals remain the immunization priority but a better understanding of susceptibility in two-dose recipients is needed to define effective interventions if elimination is to be achieved.
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ABSTRACT: Australia has achieved measles elimination as announced in March 2014 by the WHO Western Pacific Regional Committee, based on several lines of evidence. However, despite strong national evidence for elimination, there remains substantial regional variation in vaccine coverage, has resulted in recent outbreaks and potential for increased frequency in the future. In this study, we apply a multiple cohort model of measles immunity, stratified by age and local geographic area to predict trends in the measles reproduction number R. In addition, we use branching process models of outbreak risks to predict state-level probabilities of the occurrence of measles outbreaks over the next 20 years. Our results suggest increasing risks of large measles outbreaks over this period, in particular in the states of Queensland and New South Wales. In addition, there is wide variation in predicted R values by smaller geographic areas, although uncertainty in age-specific immunity limits the precision of our results. Our predictions align with observed outbreaks in Australian states and suggest our approach to determining future outbreak risks could be applied more widely in elimination or near-elimination settings. Copyright © 2015 Elsevier Ltd. All rights reserved.Vaccine 01/2015; 33(9). DOI:10.1016/j.vaccine.2014.12.071 · 3.49 Impact Factor
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ABSTRACT: Measles transmission has been well documented in healthcare facilities. Healthcare personnel who are unvaccinated and who lack other evidence of measles immunity put themselves and their patients at risk for measles. We conducted a systematic literature review of measles vaccination policies and their implementation in healthcare personnel, measles seroprevalence among healthcare personnel, measles transmission and disease burden in healthcare settings, and impact/costs incurred by healthcare facilities for healthcare-associated measles transmission. Five database searches yielded 135 relevant articles; 47 additional articles were found through cross-referencing. The risk of acquiring measles is estimated to be 2 to 19 times higher for susceptible healthcare personnel than for the general population. Fifty-three articles published worldwide during 1989-2013 reported measles transmission from patients to healthcare personnel; many of the healthcare personnel were unvaccinated or had unknown vaccination status. Eighteen articles published worldwide during 1982-2013 described examples of transmission from healthcare personnel to patients or to other healthcare personnel. Half of European countries have no measles vaccine policies for healthcare personnel. There is no global policy recommendation for the vaccination of healthcare personnel against measles. Even in countries such as the United States or Finland that have national policies, the recommendations are not uniformly implemented in healthcare facilities. Measles serosusceptibility in healthcare personnel varied widely across studies (median 6.5%, range 0-46%) but was consistently higher among younger healthcare personnel. Deficiencies in documentation of two doses of measles vaccination or other evidence of immunity among healthcare personnel presents challenges in responding to measles exposures in healthcare settings. Evaluating and containing exposures and outbreaks in healthcare settings can be disruptive and costly. Establishing policies for measles vaccination for healthcare personnel is an important strategy towards achieving measles elimination and should be a high priority for global policy setting groups, governments, and hospitals.Vaccine 11/2013; 32(38). DOI:10.1016/j.vaccine.2013.11.005 · 3.49 Impact Factor
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ABSTRACT: Asthmatics have increased risks of common and serious microbial infections including vaccine preventable diseases. Little is known about whether asthma influences waning of humoral immunity. We assessed whether asthma status influences waning of anti-measles virus antibody concentrations over time. The study utilized a cross-sectional study cohort of healthy children who had been immunized with one-dose of MMR-II at age approximately 15 months. Between 5 and 12 years of age, measles vaccine virus-specific antibody (IgG) values were measured by EIA and considered seropositive if the EIA index unit was ≥ 1. The medical records were reviewed to determine asthma status during the first 18 years of life by applying predetermined criteria for asthma. A least squares regression model was used to evaluate the effect of asthma status on the relationship between measles antibody titer and time elapsed between the initial measles vaccination and measurement of measles antibody concentrations. Of the 838 eligible children, 281 (34%) met criteria for asthma. Measles antibody waned over time (r=-0.19, p<0.001), specifically more rapidly in asthmatics (r=-0.30, p<0.001, a decrease of -0.114 unit per year) than non-asthmatics (r=-0.13, p=0.002, a decrease of -0.046 unit per year) (p-value for interaction=0.010). This differential waning rate resulted in a lower mean (SD) measles antibody concentration [1.42 (0.67) vs. 1.67 (0.69), p=0.008] and lower seropositivity rate (73% vs. 84%, p=0.038) in asthmatics than non-asthmatics starting around 9.3 years after the initial measles vaccination. Asthma status is associated with waning kinetics of measles antibody among children.The Pediatric Infectious Disease Journal 05/2014; 33(10). DOI:10.1097/INF.0000000000000375 · 3.14 Impact Factor