Disease burden attributable to respiratory syncytial virus outbreaks in long-term care.

Background: Respiratory syncytial virus (RSV) disease burden is significant among children; however, RSV can also cause excess morbidity and mortality among older adults. Populations in long-term care homes (LTCHs) may be at greater risk of exposure and increased infection severity. The objectives of this article are to identify evidence regarding disease burden and outcome severity attributable to RSV outbreaks among residents and staff in LTCHs; and to highlight reported population and outbreak characteristics. Methods: All types of evidence were eligible for inclusion. Data utilized by included studies was between the end of the 2010 H1N1 influenza pandemic and the beginning of the coronavirus disease 2019 (COVID-19) pandemic. Evidence from the following countries was considered: G7, the European Union, Australia and New Zealand. A total of 167 articles were identified; 58 full texts were analyzed and four sources of evidence were eligible for inclusion. Data related to population characteristics, outbreak type and resident and staff outcomes were manually charted. Results: There is a paucity of evidence sources pertaining to RSV outbreak burden among residents and staff in LTCHs. Outbreak duration ranged from 13 to 21 days. For each outbreak, 4-7 residents had confirmed RSV infection. Attack rates ranged from 12% to 38%. A spectrum of disease attributable to RSV outbreaks in LTCHs was identified, ranging from mild cold-like symptoms to death. Conclusion: Integration of RSV into existing respiratory pathogen surveillance programs is important to characterize susceptibility, transmissibility and virulence of RSV in at-risk populations. There is a need for public health organizations to publish the findings from outbreak investigations to provide evidence to inform RSV outbreak prevention and response in LTCH settings.

Epidemiological characteristics of human infections with avian influenza A(H5N6) virus, China and Laos: A multiple case descriptive analysis, February 2014-June 2023.

Background: The first human infection with highly pathogenic avian influenza A(H5N6) virus was reported in 2014. From then until June 30, 2023, 85 human cases with confirmed A(H5N6) infection have been reported worldwide. Objective: To address the present gap in knowledge of the overall epidemiology of human A(H5N6) infections, the epidemiological characteristics of human infection with A(H5N6) in China from February 2014 to June 2023 are described. Methods: Considering the severity of human infections with A(H5N6) virus (case fatality rate: 39%), the increased frequency of case reports from 2021 to present day, and lack of comprehensive epidemiologic analysis of all cases, we conducted a multiple-case descriptive analysis and a literature review to create an epidemiologic profile of reported human cases. Case data was obtained via a literature search and using official intelligence sources captured by the Public Health Agency of Canada's International Monitoring and Assessment Tool (IMAT), including Event Information Site posts from the World Health Organization. Results: Most human A(H5N6) cases have been reported from China (China: 84; Laos: 1), with severe health outcomes, including hospitalization and death, reported among at-risk populations. The majority (84%) of cases reported contact with birds prior to illness onset. Cases were detected throughout the course of the year, with a slight decrease in illness incidence in the warmer months. Conclusion: As A(H5N6) continues to circulate and cause severe illness, surveillance and prompt information sharing is important for creating and implementing effective public health measures to reduce the likelihood of additional human infections.

Bloodstream Infections in Children Hospitalized for Influenza, the Canadian Immunization Monitoring Program Active.

BACKGROUND: We aimed to estimate the proportion of children hospitalized for influenza whose illness was complicated by bloodstream infection, describe their clinical course, and identify the factors associated with bloodstream infection. METHODS: We performed active surveillance for laboratory-confirmed influenza hospitalizations among children ≤16 years old at the 12 Canadian Immunization Monitoring Program Active hospitals, from the 2010-2011 to 2020-2021 influenza seasons. Factors associated with bloodstream infection were identified using multivariable logistic regression analyses. RESULTS: Among 9179 laboratory-confirmed influenza hospital admissions, bloodstream infection occurred in 87 children (0.9%). Streptococcus pyogenes (22%), Staphylococcus aureus (18%) and Streptococcus pneumoniae (17%) were the most common bloodstream infection pathogens identified. Children with cancer [adjusted odds ratio (aOR): 2.78; 95% confidence interval (CI): 1.23-5.63], a laboratory-confirmed nonbloodstream bacterial infection (aOR: 14.1; 95% CI: 8.04-24.3) or radiographically-confirmed pneumonia (aOR: 1.87; 95% CI: 1.17-2.97) were more likely to experience a bloodstream infection, whereas children with chronic lung disorders were less likely (aOR: 0.41; 95% CI: 0.19-0.80). Disease severity markers such as intensive care unit admission (aOR: 2.11; 95% CI: 1.27-3.46), mechanical ventilation (aOR: 2.84; 95% CI: 1.63-4.80) and longer hospital length of stay (aOR: 1.02; 95% CI: 1.01-1.03) were associated with bloodstream infection. Bloodstream infection also increased the odds of death (aOR: 13.0; 95% CI: 4.84-29.1) after adjustment for age, influenza virus type and the presence of any at-risk chronic condition. CONCLUSIONS: Bloodstream infections, although infrequent, are associated with intensive care unit admission, mechanical ventilation, increased hospital length of stay and in-hospital mortality, thus requiring increased levels of care among pediatric influenza hospitalizations.

Outcomes of immunocompromised children hospitalized for Influenza, 2010-2021, the Canadian Immunization Monitoring Program Active (IMPACT).

OBJECTIVES: To evaluate immunocompromising conditions and subgroups of immunocompromise as risk factors for severe outcomes among children admitted for influenza. METHODS: We performed active surveillance for laboratory-confirmed influenza hospitalizations among children ≤16 years old at the 12 Canadian Immunization Monitoring Program Active hospitals, during 2010-2021. Logistic regression analyses were used to compare outcomes between immunocompromised and non-immunocompromised children, and for different subgroups of immunocompromise. The primary outcome was intensive care unit (ICU) admission; the secondary outcomes were mechanical ventilation and death. RESULTS: Among 8982 children, 892 (9.9%) were immunocompromised; these patients were older (median, 5.6 (IQR, 3.1-10.0) vs. 2.4 (1-6) years; p < 0.001) than non-immunocompromised children, had a similar frequency of comorbidities, excluding immunocompromise and/or malignancy (38% (340/892) vs. 40% (3272/8090); p 0.2), but fewer respiratory symptoms, such as respiratory distress (20% (177/892) vs. 42% (3424/8090), p < 0.001). In multivariable analyses, immunocompromise (adjusted odds ratio (aOR), 0.19; 95% CI, 0.14-0.25) and its subcategories immunodeficiency (aOR, 0.16; 95% CI, 0.10-0.23), immunosuppression (aOR, 0.17; 95% CI, 0.12-0.23), chemotherapy (aOR, 0.07; 95% CI, 0.03-0.13), and solid organ transplantation (aOR, 0.17; 95% CI, 0.06-0.37) were associated with decreased probability of ICU admission in children admitted for influenza. Immunocompromise was also associated with a decreased probability of mechanical ventilation (aOR, 0.26; 95% CI, 0.16-0.38) or death (aOR, 0.22; 95% CI, 0.03-0.72). CONCLUSION: Immunocompromised children are overrepresented among hospitalizations for influenza, but have a decreased probability of ICU admission, mechanical ventilation, and mortality following admission. Admission bias precludes generalizability beyond the hospital setting.

National influenza mid-season report, 2022-2023: A rapid and early epidemic onset.

Canada's 2022-2023 national influenza epidemic was declared in epidemiological week 43 (week ending October 29, 2022), relatively early in comparison to historical seasons. This year marks the return to pre-pandemic-like influenza circulation, following the brief and delayed influenza epidemic declared in the spring of the 2021-2022 season. To date this season, 59,459 detections of influenza have been reported out of 456,536 tests; both values exceeding historical averages. This epidemic is being fundamentally driven by influenza A, with influenza A(H3N2) accounting for 94% of subtyped detections. This season to date has had a significant impact on adolescents and young children, with a high proportion of detections occurring in those aged 0-19 years (42%). Provinces and territories have reported higher than usual influenza-associated hospitalizations, intensive care unit admissions, and deaths in comparison with previous seasons; in particular, paediatric hospitalization incidence was persistently far above historical peak levels for several weeks. The return of seasonal influenza circulation highlights the importance of sustained vigilance with regard to influenza and employment of available mitigation measures, especially of annual seasonal influenza vaccination.

Does the Australian influenza season predict the Canadian influenza season? A qualitative comparison of seasons, 2014-2020.

A commonly held belief by the Canadian media and public is that the Australian influenza season is a fairly reliable indicator of what the Canadian influenza season that follows might be like. However, this claim is not well substantiated with epidemiological evidence. Therefore, the objective of this work was to qualitatively compare the timing of the onset, peak, and intensity of influenza activity, the dominant circulating influenza strains, and the seasonal vaccine and vaccination policies from 2014 to 2020 between Canada and Australia, using a combination of FluNet data and influenza surveillance reports and publications. Across the epidemiological indicators considered, the epidemics between Canada and Australia often differ. While vaccination policies and coverage are similar between the two countries, vaccine composition and vaccine effectiveness estimates also differ. Ultimately, there are many differences and confounding variables between the Australian and Canadian influenza seasons across numerous indicators that preclude the use of the Australian influenza season as the sole predictor of the Canadian influenza season. However, the availability of global surveillance data and robust national and sub-national surveillance data can provide lead time and inform within-season resource and capacity planning, as well as mitigation measures, for seasonal influenza epidemics.

Antigenic drift and epidemiological severity of seasonal influenza in Canada.

Seasonal influenza epidemics circulate globally every year with varying levels of severity. One of the major drivers of this seasonal variation is thought to be the antigenic drift of influenza viruses, resulting from the accumulation of mutations in viral surface proteins. In this study, we aimed to investigate the association between the genetic drift of seasonal influenza viruses (A/H1N1, A/H3N2 and B) and the epidemiological severity of seasonal epidemics within a Canadian context. We obtained hemagglutinin protein sequences collected in Canada between the 2006/2007 and 2019/2020 flu seasons from GISAID and calculated Hamming distances in a sequence-based approach to estimating inter-seasonal antigenic differences. We also gathered epidemiological data on cases, hospitalizations and deaths from national surveillance systems and other official sources, as well as vaccine effectiveness estimates to address potential effect modification. These aggregate measures of disease severity were integrated into a single seasonal severity index. We performed linear regressions of our severity index with respect to the inter-seasonal antigenic distances, controlling for vaccine effectiveness. We did not find any evidence of a statistical relationship between antigenic distance and seasonal influenza severity in Canada. Future studies may need to account for additional factors, such as co-circulation of other respiratory pathogens, population imprinting, cohort effects and environmental parameters, which may drive seasonal influenza severity.

National FluWatch mid-season report, 2021-2022: Sporadic influenza activity returns.

Surveillance for Canada's 2021-2022 seasonal influenza epidemic began in epidemiological week 35 (the week starting August 29, 2021) during the ongoing coronavirus disease 2019 (COVID-19) global public health emergency. In the 2021-2022 surveillance season to date, there has been a return of persistent sporadic influenza activity, and the first influenza-associated hospitalizations since mid-2020 have been reported. However, as of week 52 (week ending 01/01/2022) activity has remained sporadic, and no influenza-confirmed outbreaks or epidemic activity have been detected. There has been a delay or absence in several traditional seasonal influenza milestones, including the declared start of the influenza season, marked by a threshold of 5% positivity, which historically has occurred on average in week 47. The 429 sporadic detections reported in Canada to date have occurred in 31 regions across seven provinces/territories. Nearly half (n=155/335, 46.3%) of reported cases have been in the paediatric (younger than 19 years) population. Three-quarters of the cases were influenza A detections (n=323/429, 75.3%). Of the subtyped influenza A detections, A(H3N2) predominated (n=83/86, 96.5%). Of the 12 viruses characterized by the National Microbiology Laboratory, 11 were seasonal strains. Among the seasonal strains characterized, only one was antigenically similar to the strains recommended for the 2021-2022 Northern Hemisphere vaccine, though all were sensitive to the antivirals, oseltamivir and zanamivir. Until very recently, seasonal influenza epidemics had not been reported since March 2020. Evidence on the re-emergence of seasonal influenza strains in Canada following the A(H1N1)pdm09 pandemic shows that influenza A(H3N2) and B epidemics ceased through the 2009-2010 season and second wave of A(H1N1)pdm09, but then re-emerged in subsequent seasons to predominate causing epidemics of higher intensity than in the pre-pandemic seasons. When and where seasonal influenza epidemic activity resumes cannot be predicted, but model-based estimates and historical post-pandemic patterns of intensified epidemics warrant continued vigilance through the usual season and for out-of-season re-emergence. In addition, ongoing population preparedness measures, such as annual influenza vaccination to mitigate the intensity and burden of future seasonal influenza epidemic waves, should continue.

Implications of the unexpected persistence of human rhinovirus/enterovirus during the COVID-19 pandemic in Canada.

Stringent public health measures imposed across Canada to control the COVID-19 pandemic have nearly suppressed most seasonal respiratory viruses, with the notable exception of human rhinovirus/enterovirus (hRV/EV). Thanks to this unexpected persistence, we highlight that hRV/EV could serve as a sentinel for levels of contact rate in populations to inform on the efficiency, or the need of, public health measures to control the subsequent COVID-19 epidemic, but also for future epidemics from other seasonal or emerging respiratory pathogens.

National Influenza Annual Report, Canada, 2021-2022: A brief, late influenza epidemic.

Canadian seasonal influenza circulation had been suppressed since the beginning of the coronavirus disease 2019 (COVID-19) pandemic. This suppression was reported globally and generated concern that the return of community influenza circulation could be intense and that co-circulation of influenza and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was possible and potentially severe. Community circulation of influenza returned to Canada during the 2021-2022 influenza season. The influenza epidemic began in week 16 (mid-April 2022) and lasted only nine weeks. This epidemic was driven by influenza A(H3N2) and was exceptionally late in the season, low in intensity and short in length. Community co-circulation of influenza and SARS-CoV-2 was observed in Canada for the first time during the 2021-2022 seasonal influenza epidemic. The unusual characteristics of the 2021-2022 influenza epidemic suggest that a breadth of factors moderate transmission dynamics of the two viruses. Concerns of an intense seasonal influenza epidemic did not come to fruition during the 2021-2022 season; therefore, high influenza susceptibility remains, as does predisposition to larger influenza epidemics. Ongoing circulation of SARS-CoV-2 creates uncertainty about dynamics of future influenza epidemics, but influenza vaccination remains a key public health intervention available to protect Canadians. Public health authorities need to remain vigilant, maintain surveillance and continue to plan for both heightened seasonal influenza circulation and for the potential for endemic co-circulation of influenza and SARS-CoV-2.

National Influenza Annual Report, Canada, 2020-2021, in the global context.

During the 2020-2021 Canadian influenza season, no community circulation of influenza occurred. Only 69 positive detections of influenza were reported, and influenza percent positivity did not exceed 0.1%. Influenza indicators were at historical lows compared with the previous six seasons, with no laboratory-confirmed influenza outbreaks or severe outcomes being reported by any of the provinces and territories. Globally, influenza circulation was at historically low levels in both the Northern and the Southern Hemispheres. The decreased influenza activity seen in Canada and globally is concurrent with the implementation of non-pharmaceutical public health measures to mitigate the spread of the coronavirus disease 2019 (COVID-19). Although it is difficult to predict when influenza will begin to re-circulate, given the increased COVID-19 vaccination and the relaxation of public health measures, an influenza resurgence can be expected and may be more severe or intense than recent seasons. Influenza vaccination, along with non-pharmaceutical public health measures, continues to remain the best method to prevent the spread and impact of influenza. Public health authorities need to remain vigilant, maintain surveillance and continue to plan for heightened seasonal influenza circulation.

FluWatchers: Evaluation of a crowdsourced influenza-like illness surveillance application for Canadian influenza seasons 2015-2016 to 2018-2019.

BACKGROUND: Sentinel influenza-like illness (ILI) surveillance is an essential component of a comprehensive influenza surveillance program. Community-based ILI surveillance systems that rely solely on sentinel healthcare practices omit important segments of the population, including those who do not seek medical care. Participatory surveillance, which relies on community participation in surveillance, may address some limitations of traditional ILI systems. OBJECTIVE: We aimed to evaluate FluWatchers, a crowdsourced ILI application developed to complement and complete ILI surveillance in Canada. METHODS: Using established frameworks for surveillance evaluations, we assessed the acceptability, reliability, accuracy and usefulness of the FluWatchers system 2015-2016, through 2018-2019. Evaluation indicators were compared against national surveillance indicators of ILI and of laboratory confirmed respiratory virus infections. RESULTS: The acceptability of FluWatchers was demonstrated by growth of 50%-100% in season-over-season participation, and a consistent season-over-season retention of 80%. Reliability was greater for FluWatchers than for our traditional ILI system, although both systems had week-over-week fluctuations in the number of participants responding. FluWatchers' ILI rates had moderate correlation with weekly influenza laboratory detection rates and other winter seasonal respiratory virus detections including respiratory syncytial virus and seasonal coronaviruses. Finally, FluWatchers has demonstrated its usefulness as a source of core FluWatch surveillance information and has the potential to fill data gaps in current programs for influenza surveillance and control. CONCLUSION: FluWatchers is an example of an innovative digital participatory surveillance program that was created to address limitations of traditional ILI surveillance in Canada. It fulfills the surveillance system evaluation criteria of acceptability, reliability, accuracy and usefulness.

Representativeness of the FluWatchers Participatory Disease Surveillance Program 2015-2016 to 2018-2019: How do participants compare with the Canadian population?

BACKGROUND: FluWatch is Canada's national surveillance system that monitors the spread of influenza. Its syndromic surveillance component monitors the spread of influenza-like illness (ILI) in near-real time for signals of unusual or increased activity. Syndromic surveillance data are collected from two main sources: the Sentinel Practitioner ILI Reporting System and FluWatchers.We evaluated the representativeness of the most recent participant population to understand changes in representativeness since 2015, to identify demographic and geographic gaps and correlates/determinants of participation to characterize a typical participant. METHODS: In this serial cross-sectional study, characteristics of participants during four consecutive influenza seasons (2015-2016, 2016-2017, 2017-2018 and 2018-2019) were compared with the 2016 Canadian Census and the 2015-2016, 2016-2017, 2017-2018 and 2018-2019 National Seasonal Influenza Vaccination Coverage Surveys. Associations between demographic factors and the level of user participation were also analyzed among the 2018-2019 FluWatchers population. RESULTS: Infants (0-4 years) and older adults (65 years and older) were under-represented in FluWatchers across all four influenza seasons. Female and urban participants were significantly over-represented. Vaccination coverage remained significantly higher among the FluWatchers populations from the past four influenza seasons across all age groups. Level of participation among FluWatchers was associated with age and vaccination status, but not with sex or geography. Over its four years of implementation, the FluWatchers participant population became more representative of the Canadian population with respect to age and geography (urban/rural and provincial/territorial). CONCLUSION: FluWatchers participants under-represent the tails of Canada's age distribution and over-represent those who engage in health promoting behaviours as indicated by high influenza vaccine coverage, consistent with typical volunteer-based survey response biases. Representativeness would likely improve with targeted recruitment of under-represented groups, such as males, older adults and Canadians living in rural areas.

Antiviral Use in Canadian Children Hospitalized for Influenza.

OBJECTIVES: Antivirals are recommended for children hospitalized with influenza but are underutilized. We describe antiviral prescribing during influenza admissions in Canadian pediatric centers and identify factors associated with antiviral use. METHODS: We performed active surveillance for laboratory-confirmed influenza hospitalizations among children ≤16 years old at the 12 Canadian Immunization Monitoring Program Active hospitals, from 2010-2011 to 2018-2019. Logistic regression analyses were used to identify factors associated with antiviral use. RESULTS: Among 7545 patients, 57.4% were male; median age was 3 years (interquartile range: 1.1-6.3). Overall, 41.3% received antiviral agents; 72.8% received antibiotics. Antiviral use varied across sites (range, 10.2% to 81.1%) and influenza season (range, 19.9% to 59.6%) and was more frequent in children with ≥1 chronic health condition (52.7% vs 36.7%; P < .001). On multivariable analysis, factors associated with antiviral use included older age (adjusted odds ratio [aOR] 1.04 [95% confidence interval (CI), 1.02-1.05]), more recent season (highest aOR 9.18 [95% CI, 6.70-12.57] for 2018-2019), admission during peak influenza period (aOR 1.37 [95% CI, 1.19-1.58]), availability of local treatment guideline (aOR 1.54 [95% CI, 1.17-2.02]), timing of laboratory confirmation (highest aOR 2.67 [95% CI, 1.97-3.61] for result available before admission), presence of chronic health conditions (highest aOR 4.81 [95% CI, 3.61-6.40] for cancer), radiographically confirmed pneumonia (aOR 1.39 [95% CI, 1.20-1.60]), antibiotic treatment (aOR 1.51 [95% CI, 1.30-1.76]), respiratory support (1.57 [95% CI, 1.19-2.08]), and ICU admission (aOR 3.62 [95% CI, 2.88-4.56]). CONCLUSIONS: Influenza antiviral agents were underused in Canadian pediatric hospitals, including among children with high-risk chronic health conditions. Prescribing varied considerably across sites, increased over time, and was associated with patient and hospital-level characteristics. Multifaceted hospital-based interventions are warranted to strengthen adherence to influenza treatment guidelines and antimicrobial stewardship practices.

The impact of the COVID-19 pandemic on influenza, respiratory syncytial virus, and other seasonal respiratory virus circulation in Canada: A population-based study.

BACKGROUND: The ongoing coronavirus disease 2019 (COVID-19) pandemic has resulted in implementation of public health measures worldwide to mitigate disease spread, including; travel restrictions, lockdowns, messaging on handwashing, use of face coverings and physical distancing. As the pandemic progresses, exceptional decreases in seasonal respiratory viruses are increasingly reported. We aimed to evaluate the impact of the pandemic on laboratory confirmed detection of seasonal non-SARS-CoV-2 respiratory viruses in Canada. METHODS: Epidemiologic data were obtained from the Canadian Respiratory Virus Detection Surveillance System. Weekly data from the week ending 30th August 2014 until the week ending the 13th March 2021 were analysed. We compared trends in laboratory detection and test volumes during the 2020/2021 season with pre-pandemic seasons from 2014 to 2019. FINDINGS: We observed a dramatically lower percentage of tests positive for all seasonal respiratory viruses during 2020-2021 compared to pre-pandemic seasons. For influenza A and B the percent positive decreased to 0•0015 and 0•0028 times that of pre-pandemic levels respectively and for RSV, the percent positive dropped to 0•0169 times that of pre-pandemic levels. Ongoing detection of enterovirus/rhinovirus occurred, with regional variation in the epidemic patterns and intensity. INTERPRETATION: We report an effective absence of the annual seasonal epidemic of most seasonal respiratory viruses in 2020/2021. This dramatic decrease is likely related to implementation of multi-layered public health measures during the pandemic. The impact of such measures may have relevance for public health practice in mitigating seasonal respiratory virus epidemics and for informing responses to future respiratory virus pandemics. FUNDING: No additional funding source was required for this study.

The performance of phenomenological models in providing near-term Canadian case projections in the midst of the COVID-19 pandemic: March - April, 2020.

BACKGROUND: The COVID-19 pandemic has had an unprecedented impact on citizens and health care systems globally. Valid near-term projections of cases are required to inform the escalation, maintenance and de-escalation of public health measures, and for short-term health care resource planning. METHODS: Near-term case and epidemic growth rate projections for Canada were estimated using three phenomenological models: the logistic model, Generalized Richard's model (GRM) and a modified Incidence Decay and Exponential Adjustment (m-IDEA) model. Throughout the COVID-19 epidemic in Canada, these models have been validated against official national epidemiological data on an ongoing basis. RESULTS: The best-fit models estimated that the number of COVID-19 cases predicted to be reported in Canada as of April 1, 2020 and May 1, 2020 would be 11,156 (90 % prediction interval: 9,156-13,905) and 54,745 (90 % prediction interval: 54,252-55,239). The three models varied in their projections and their performance over the first seven weeks of their implementation. Both the logistic model and GRM under-predicted cases reported a week following the projection date in nearly all instances. The logistic model performed best at the early stages, the m-IDEA model performed best at the later stages, and the GRM performed most consistently during the full period assessed. CONCLUSIONS: All three models have yielded qualitatively comparable near-term forecasts of cases and epidemic growth for Canada. Under or over-estimation of projected cases and epidemic growth by these models could be associated with changes in testing policies and/or public health measures. Simple forecasting models can be invaluable in projecting the changes in trajectory of subsequent waves of cases to provide timely information to support the pandemic response.

National influenza mid-season report, 2020-2021.

Canada's national influenza season typically starts in the latter half of November (week 47) and is defined as the week when at least 5% of influenza tests are positive and a minimum of 15 positive tests are observed. As of December 12, 2020 (week 50), the 2020-2021 influenza season had not begun. Only 47 laboratory-confirmed influenza detections were reported from August 23 to December 12, 2020; an unprecedentedly low number, despite higher than usual levels of influenza testing. Of this small number of detections, 64% were influenza A and 36% were influenza B. Influenza activity in Canada was at historically low levels compared with the previous five seasons. Provinces and territories reported no influenza-associated adult hospitalizations. Fewer than five hospitalizations were reported by the paediatric sentinel hospitalization network. With little influenza circulating, the National Microbiology Laboratory had not yet received samples of influenza viruses collected during the 2020-2021 season for strain characterization or antiviral resistance testing. The assessment of influenza vaccine effectiveness, typically available in mid-March, is expected to be similarly limited if low seasonal influenza circulation persists. Nevertheless, Canada's influenza surveillance system remains robust and has pivoted its syndromic, virologic and severe outcomes system components to support coronavirus disease 2019 (COVID-19) surveillance. Despite the COVID-19 pandemic, the threat of influenza epidemics and pandemics persists. It is imperative 1) to maintain surveillance of influenza, 2) to remain alert to unusual or unexpected events and 3) to be prepared to mitigate influenza epidemics when they resurge.

Effets projetés des mesures de santé publique non pharmacologiques visant à prévenir la recrudescence de la transmission du SRAS-CoV-2 au Canada.

CONTEXTE: Il faudra prendre des mesures continues contre la transmission communautaire du coronavirus du syndrome respiratoire aigu sévère 2 (SRAS-CoV-2) pour prévenir d'autres vagues d'infection. Nous avons exploré les effets des interventions non pharmacologiques sur la transmission projetée du SRAS-CoV-2 au Canada. MÉTHODES: Nous avons créé un modèle de la population canadienne à base d'agents intégrant l'âge qui simule les effets des mesures de santé publique, selon leur intensité actuelle et projetée, sur la transmission du SRAS-CoV-2. Les mesures étudiées sont le dépistage et l'isolement des cas, la recherche de contacts et la mise en quarantaine, l'éloignement sanitaire et la fermeture des espaces partagés. Nous avons évalué l'effet des mesures prises individuellement et celui des mesures combinées. RÉSULTATS: En l'absence de mesures, 64,6 % (intervalle de crédibilité [ICr] à 95 % : 63,9 %­65,0 %) des Canadiens contracteraient le SRAS-CoV-2 (taux d'attaque global), et 3,6 % (ICr à 95 % 2,4 %­3,8 %) des personnes infectées en mourraient. En poursuivant le dépistage et la recherche de contacts à la même intensité que pendant la période de référence, sans maintenir l'éloignement sanitaire ou refermer certains endroits, le pays connaîtrait un taux d'attaque global de 56,1 % (ICr à 95 % 0,05 %­57,1 %); si ces mesures étaient accrues, le taux d'attaque chuterait à 0,4 % (ICr à 95 % 0,03 %­23,5 %). En combinant ce dernier scénario et le maintien de l'éloignement sanitaire, le taux tomberait à 0,2 % (ICr à 95 % 0,03 %­1,7 %). Ce scénario est le seul qui garderait la demande en soins hospitaliers et intensifs sous la capacité, qui préviendrait presque tous les décès et qui mettrait fin à l'épidémie. La prolongation de la fermeture des écoles aurait un effet minime, mais réduirait la transmission en milieu scolaire. Par contre, la prolongation de la fermeture des lieux de travail et des lieux publics réduirait de manière marquée le taux d'attaque et mettait habituellement ou toujours fin à l'épidémie, selon les différents scénarios simulés. INTERPRÉTATION: Le contrôle de la transmission du SRAS-CoV-2 passera par l'amélioration et le maintien des mesures, tant communautaires qu'individuelles. Autrement, il y aura une recrudescence de l'épidémie, et un risque de surcharger le système de santé.