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Since the end of November 2023, the European Mortality Monitoring Network (EuroMOMO) has observed excess mortality in Europe. During weeks 48 2023-6 2024, preliminary results show a substantially increased rate of 95.3 (95% CI:  91.7-98.9) excess all-cause deaths per 100,000 person-years for all ages. This excess mortality is seen in adults aged 45 years and older, and coincides with widespread presence of COVID-19, influenza and respiratory syncytial virus (RSV) observed in many European countries during the 2023/24 winter season.

Introduction: Influenza vaccination, besides protecting traditional risk groups, can protect employees and reduce illness-related absence, which is especially relevant in sectors with staff shortages. This study describes current knowledge of influenza vaccination in teachers and estimates its potential impact., Methods: We conducted a scoping review of the considerations for and impact of influenza vaccination of schoolteachers (grey and scientific literature up to 2020 March, complemented with interviews). We then estimated the potential impact of teacher vaccination in the Netherlands, with different scenarios of vaccine uptake for 3 influenza seasons (2016-2019). Using published data on multiple input parameters, we calculated potentially averted absenteeism notifications, averted absenteeism duration and averted doctor visits for influenza., Results: Only one scientific paper reported on impact; it showed lower absenteeism in vaccinated teachers, whereas more knowledge of vaccination impact was deemed crucial by 50% of interviewed experts. The impact for the Netherlands of a hypothetical 50% vaccine uptake was subsequently estimated: 74-293 potentially averted physician visits and 11,178-28,896 potentially averted days of influenza absenteeism (on ≈200,000 total teacher population). An estimated 12-32 vaccinations were required to prevent one teacher sick-leave notification, or 3.5-9.1 vaccinations to prevent one day of teacher absenteeism (2016-2019)., Conclusion: Scientific publications on influenza vaccination in teachers are few, while public interest has increased to reduce teacher shortages. However, school boards and public health experts indicate requiring knowledge of impact when considering this vaccination. Estimations of 3.5-9.1 vaccinated teachers preventing one day of influenza-related sick leave suggest a possible substantial vaccination impact on absenteeism. Financial incentives, more accessible on-site vaccinations at workplaces, or both, are expected to increase uptake, but more research is needed on teachers' views and vaccine uptake potential and its cost-effectiveness. Piloting free on-site influenza vaccination in several schools could provide further information on teacher participation., Competing Interests: The authors have declared that no competing interests exist.

Background: The burden of severe influenza virus infections is poorly known, for which surveillance of severe acute respiratory infection (SARI) is encouraged. Hospitalized SARI patients are however not always tested for influenza virus infection. Thus, to estimate the impact of influenza circulation we studied how influenza in primary care relates to intensive care unit (ICU) admissions using a modelling approach., Methods: We used time-series regression modelling to estimate a) the number of SARI admissions to ICU associated with medically attended influenza infections in primary care; b) how this varies by season; and c) the time lag between SARI and influenza time series. We analysed weekly adult ICU admissions (registry data) and adult influenza incidence (primary care surveillance data) from July 2007 through June 2016., Results: Depending on the year, 0% to 12% of annual SARI admissions were associated with influenza (0-554 in absolute numbers; population rate: 0/10 000-0.39/10 000 inhabitants), up to 27% during influenza epidemics. The average optimal fitting lag was +1 week (SARI trend preceding influenza by 1 week), varying between seasons (-1 to +4) with most seasons showing positive lags., Conclusion: Up to 12% of yearly SARI admissions to adult ICU are associated with influenza, but with large year-to-year variation and higher during influenza epidemics. In most years, SARI increases earlier than medically attended influenza infections in the general population. SARI surveillance could thus complement influenza-like illness surveillance by providing an indication of the season-specific burden of severe influenza infections and potential early warning of influenza activity and severity., (© 2020 The Authors. Influenza and Other Respiratory Viruses published by John Wiley & Sons Ltd.)

Background: Ambulance dispatches could be useful for syndromic surveillance of severe respiratory infections. We evaluated whether ambulance dispatch calls of highest urgency reflect the circulation of influenza A virus, influenza B virus, respiratory syncytial virus (RSV), rhinovirus, adenovirus, coronavirus, parainfluenzavirus and human metapneumovirus (hMPV)., Methods: We analysed calls from four ambulance call centres serving 25% of the population in the Netherlands (2014-2016). The chief symptom and urgency level is recorded during triage; we restricted our analysis to calls with the highest urgency and identified those compatible with a respiratory syndrome. We modelled the relation between respiratory syndrome calls (RSC) and respiratory virus trends using binomial regression with identity link function., Results: We included 211 739 calls, of which 15 385 (7.3%) were RSC. Proportion of RSC showed periodicity with winter peaks and smaller interseasonal increases. Overall, 15% of RSC were attributable to respiratory viruses (20% in out-of-office hour calls). There was large variation by age group: in <15 years, only RSV was associated and explained 11% of RSC; in 15-64 years, only influenza A (explained 3% of RSC); and in ≥65 years adenovirus explained 9% of RSC, distributed throughout the year, and hMPV (4%) and influenza A (1%) mainly during the winter peaks. Additionally, rhinovirus was associated with total RSC., Conclusion: High urgency ambulance dispatches reflect the burden of different respiratory viruses and might be useful to monitor the respiratory season overall. Influenza plays a smaller role than other viruses: RSV is important in children while adenovirus and hMPV are the biggest contributors to emergency calls in the elderly., (© 2020 The Authors. Influenza and Other Respiratory Viruses Published by John Wiley & Sons Ltd.)

Background: While influenza-like-illness (ILI) surveillance is well-organized at primary care level in Europe, few data are available on more severe cases. With retrospective data from intensive care units (ICU) we aim to fill this current knowledge gap. Using multiple parameters proposed by the World Health Organization we estimate the burden of severe acute respiratory infections (SARI) in the ICU and how this varies between influenza epidemics., Methods: We analyzed weekly ICU admissions in the Netherlands (2007-2016) from the National Intensive Care Evaluation (NICE) quality registry (100% coverage of adult ICUs in 2016; population size 14 million) to calculate SARI incidence, SARI peak levels, ICU SARI mortality, SARI mean Acute Physiology and Chronic Health Evaluation (APACHE) IV score, and the ICU SARI/ILI ratio. These parameters were calculated both yearly and per separate influenza epidemic (defined epidemic weeks). A SARI syndrome was defined as admission diagnosis being any of six pneumonia or pulmonary sepsis codes in the APACHE IV prognostic model. Influenza epidemic periods were retrieved from primary care sentinel influenza surveillance data., Results: Annually, an average of 13% of medical admissions to adult ICUs were for a SARI but varied widely between weeks (minimum 5% to maximum 25% per week). Admissions for bacterial pneumonia (59%) and pulmonary sepsis (25%) contributed most to ICU SARI. Between the eight different influenza epidemics under study, the value of each of the severity parameters varied. Per parameter the minimum and maximum of those eight values were as follows: ICU SARI incidence 558-2400 cumulated admissions nationwide, rate 0.40-1.71/10,000 inhabitants; average APACHE score 71-78; ICU SARI mortality 13-20%; ICU SARI/ILI ratio 8-17 cases per 1000 expected medically attended ILI in primary care); peak-incidence 101-188 ICU SARI admissions in highest-incidence week, rate 0.07-0.13/10,000 population)., Conclusions: In the ICU there is great variation between the yearly influenza epidemic periods in terms of different influenza severity parameters. The parameters also complement each other by reflecting different aspects of severity. Prospective syndromic ICU SARI surveillance, as proposed by the World Health Organization, thereby would provide insight into the severity of ongoing influenza epidemics, which differ from season to season.

Background: Viral interaction in which outbreaks of influenza and other common respiratory viruses might affect each other has been postulated by several short studies. Regarding longer time periods, influenza epidemics occasionally occur very early in the season, as during the 2009 pandemic. Whether early occurrence of influenza epidemics impacts outbreaks of other common seasonal viruses is not clear., Objectives: We investigated whether early occurrence of influenza outbreaks coincides with shifts in the occurrence of other common viruses, including both respiratory and non-respiratory viruses., Methods: We investigated time trends of and the correlation between positive laboratory diagnoses of eight common viruses in the Netherlands over a 10-year time period (2003-2012): influenza viruses types A and B, respiratory syncytial virus (RSV), rhinovirus, coronavirus, norovirus, enterovirus, and rotavirus. We compared trends in viruses between early and late influenza seasons., Results: Between 2003 and 2012, influenza B, RSV, and coronavirus showed shifts in their occurrence when influenza A epidemics occurred earlier than usual (before week 1). Although shifts were not always consistently of the same type, when influenza type A hit early, RSV outbreaks tended to be delayed, coronavirus outbreaks tended to be intensified, and influenza virus type B tended not to occur at all. Occurrence of rhinovirus, norovirus, rotavirus, and enterovirus did not change., Conclusion: When influenza A epidemics occured early, timing of the epidemics of several respiratory winter viruses usually occurring close in time to influenza A was affected, while trends in rhinoviruses (occurring in autumn) and trends in enteral viruses were not., (© 2015 The Authors. Influenza and Other Respiratory Viruses Published by John Wiley & Sons Ltd.)

Incidence of pneumococcal disease is disproportionally high in infants and elderly. Nasopharyngeal colonisation by Streptococcus pneumoniae is considered a prerequisite for disease but unlike in children, carriage in elderly is rarely detected. Here, we tested for S. pneumoniae in nasopharyngeal and saliva samples collected from community-dwelling elderly with influenza-like-illness (ILI). Trans-nasal nasopharyngeal, trans-oral nasopharyngeal and saliva samples (n = 270 per sample type) were collected during winter/spring 2011/2012 from 135 persons aged 60-89 at onset of ILI and 7-9 weeks later following recovery. After samples were tested for pneumococci by conventional culture, all plate growth was collected. DNA extracted from plate harvests was tested by quantitative-PCRs (qPCR) specific for S. pneumoniae and serotypes included in the 13-valent pneumococcal conjugated vaccine (PCV13). Pneumococci were cultured from 14 of 135 (10%) elderly with none of the sampled niches showing superiority in carriage detection. With 76/270 (28%) saliva, 31/270 (11%) trans-oral and 13/270 (5%) trans-nasal samples positive by qPCR, saliva was superior to nasopharyngeal swabs (p<0.001) in qPCR-based carriage detection. Overall, from all methods used in the study, 65 of 135 (48%) elderly carried pneumococci at least once and 26 (19%) at both study time points. The difference between carriage prevalence at ILI (n = 49 or 36%) versus recovery (n = 42 or 31%) was not significant (p = 0.38). At least 23 of 91 (25%) carriage events in 19 of 65 (29%) carriers were associated with PCV13-serotypes. We detected a large reservoir of pneumococci in saliva of elderly, with PCV13-serotype distribution closely resembling the contemporary carriage of serotypes reported in the Netherlands for PCV-vaccinated infants.

Background: During the 2009 influenza pandemic period, routine surveillance of influenza-like-illness (ILI) was conducted in The Netherlands by a network of sentinel general practitioners (GPs). In addition during the pandemic period, four other ILI/influenza surveillance systems existed. For pandemic preparedness, we evaluated the performance of the sentinel system and the others to assess which of the four could be useful additions in the future. We also assessed whether performance of the five systems was influenced by media reports during the pandemic period., Methods: The trends in ILI consultation rates reported by sentinel GPs from 20 April 2009 through 3 January 2010 were compared with trends in data from the other systems: ILI cases self-reported through the web-based Great Influenza Survey (GIS); influenza-related web searches through Google Flu Trends (GFT); patients admitted to hospital with laboratory-confirmed pandemic influenza, and detections of influenza virus by laboratories. In addition, correlations were determined between ILI consultation rates of the sentinel GPs and data from the four other systems. We also compared the trends of the five surveillance systems with trends in pandemic-related newspaper and television coverage and determined correlation coefficients with and without time lags., Results: The four other systems showed similar trends and had strong correlations with the ILI consultation rates reported by sentinel GPs. The number of influenza virus detections was the only system to register a summer peak. Increases in the number of newspaper articles and television broadcasts did not precede increases in activity among the five surveillance systems., Conclusions: The sentinel general practice network should remain the basis of influenza surveillance, as it integrates epidemiological and virological information and was able to maintain stability and continuity under pandemic pressure. Hospital and virological data are important during a pandemic, tracking the severity, molecular and phenotypic characterization of the viruses and confirming whether ILI incidence is truly related to influenza virus infections. GIS showed that web-based, self-reported ILI can be a useful addition, especially if virological self-sampling is added and an epidemic threshold could be determined. GFT showed negligible added value.

Background: Because there may be substantial hidden mortality caused by common seasonal pathogens, we estimated the number of deaths in elderly persons attributable to viruses and bacteria for which robust weekly laboratory surveillance data were available., Methods: On weekly time series (1999-2007) we used regression models to associate total death counts in individuals aged 65-74, 75-84, and ≥85 years (a population of 2.5 million) with pathogen circulation-influenza A (season-specific), influenza B, respiratory syncytial virus (RSV), parainfluenza, enterovirus, rotavirus, norovirus, Campylobacter, and Salmonella-adjusted for extreme outdoor temperatures., Results: Influenza A and RSV were significantly (P < .05) associated with mortality in all studied age groups; influenza B and parainfluenza were additionally associated in those aged ≥75 years, and norovirus was additionally associated in those aged ≥85 years. The proportions of deaths attributable to seasonal viruses were 6.8% (≥85 years), 4.4% (75-84 years), and 1.4% (65-74 years), but with great variations between years. Influenza occasionally showed lower impact than some of the other viruses., Conclusions: The number of different pathogens associated with mortality in the older population increases with increasing age. Besides influenza A and RSV, influenza B, parainfluenza and norovirus may also contribute substantially to elderly mortality.

Objective: To investigate whether a single optimal vaccination strategy exists across countries to deal with a future influenza pandemic by comparing the cost effectiveness of different strategies in various pandemic scenarios for three European countries., Design: Economic and epidemic modelling study., Settings: General populations in Germany, the Netherlands, and the United Kingdom., Data Sources: Country specific patterns of social contact and demographic data., Model: An age structured susceptible-exposed-infected-recovered transmission model that describes how an influenza A virus will spread in the populations of Germany, the Netherlands, and the United Kingdom., Interventions: Comparison of four vaccination strategies: no vaccination, blanket vaccination, vaccination of elderly people (≥ 65 years), and vaccination of high transmitters (5-19 years). The four strategies were evaluated for scenarios in which a vaccine became available early or at the peak of the pandemic, and in which either everyone was initially susceptible or older age groups had pre-existing immunity., Main Outcome Measure: Cost per quality adjusted life years (QALYs) gained., Results: All vaccination strategies were cost effective (incremental cost per QALY gained, comparing intervention with non-intervention). In scenarios where the vaccine became available at the peak of the pandemic and there was pre-existing immunity among elderly people the incremental cost effectiveness ratios for vaccinating high transmitters were €7325 (£5815; $10,470) per QALY gained for Germany, €10,216 per QALY gained for the Netherlands, and €7280 per QALY gained for the United Kingdom. The most cost effective strategy not only differed across the pandemic scenarios but also between countries. Specifically, when the vaccine was available early in the pandemic and there was no pre-existing immunity, in Germany it would be most cost effective to vaccinate elderly people ( €940 per QALY gained), whereas it would be most cost effective to vaccinate high transmitters in both the Netherlands (€525 per QALY gained) and the United Kingdom (€163 per QALY gained). This difference in optimal strategies was due to differences in the demographic characteristics of the countries: Germany has a significantly higher proportion of elderly people compared with the Netherlands and the United Kingdom., Conclusions: No single vaccination strategy was most cost effective across countries. With aging populations, pre-existing immunity in particular could be of crucial importance for the cost effectiveness of options to mitigate a future influenza pandemic.

Background: The disease burden of the 2009 influenza pandemic has been debated but reliable estimates are lacking. To guide future policy and control, these estimates are necessary. This study uses burden of disease measurements to assess the contribution of the pandemic influenza A(H1N1) virus to the overall burden of disease in the Netherlands., Methods: The burden of disease caused by 2009 pandemic influenza was estimated by calculating Disability Adjusted Life Years (DALY), a composite measure that combines incidence, sequelae and mortality associated with a disease, taking duration and severity into account. Available influenza surveillance data sources (primary care sentinel surveillance, notification data on hospitalizations and deaths and death registries) were used. Besides a baseline scenario, five alternative scenarios were used to assess effects of changing values of input parameters., Results: The baseline scenario showed a loss of 5800 DALY for the Netherlands (35 DALY per 100 000 population). This corresponds to 0.13% of the estimated annual disease burden in the Netherlands and is comparable to the estimated disease burden of seasonal influenza, despite a different age distribution in incidence and mortality of the pandemic compared to seasonal influenza., Conclusions: This disease burden estimate confirmed that, although there was a higher mortality observed among young people, the 2009 pandemic was overall a mild influenza epidemic. The disease burden of this pandemic was comparable to the burden of seasonal influenza in the Netherlands.

Conventional (static) models used in health economics implicitly assume that the probability of disease exposure is constant over time and unaffected by interventions. For transmissible infectious diseases this is not realistic and another class of models is required, so-called dynamic models. This study aims to examine the differences between one dynamic and one static model, estimating the effects of therapeutic treatment with antiviral (AV) drugs during an influenza pandemic in the Netherlands. Specifically, we focus on the sensitivity of the cost-effectiveness ratios to model choice, to the assumed drug coverage, and to the value of several epidemiological factors. Therapeutic use of AV-drugs is cost-effective compared with non-intervention, irrespective of which model approach is chosen. The findings further show that: (1) the cost-effectiveness ratio according to the static model is insensitive to the size of a pandemic, whereas the ratio according to the dynamic model increases with the size of a pandemic; (2) according to the dynamic model, the cost per infection and the life-years gained per treatment are not constant but depend on the proportion of cases that are treated; and (3) the age-specific clinical attack rates affect the sensitivity of cost-effectiveness ratio to model choice.