Spanish Influenza Surveillance System Research Articles

Burden of influenza in Spanish pediatric population and the benefit of vaccination

IntroductionThe burden of influenza in the paediatric population is often underestimated by healthcare professionals and the general population, mainly due to poor perception of its clinical importance at the individual level and its health impact at the healthcare level. The aim of this review was to collect data on the burden of paediatric influenza in Spain and to compare them with data of countries where vaccination strategies for healthy paediatric populations have been implemented. MethodsWe collected data on the burden of paediatric influenza in Spain through a systematic search of literature published between 2016–2021 (PRISMA methodology). We conducted a review of reports from the Spanish Influenza Surveillance System (SVGE) (2010–2011 to 2019–2020) and of international reports (from Canada, Finland, USA, and UK) through a systematic (2016–2021) and pragmatic search. Results1366 articles were obtained from the systematic searches by country; 26 met the inclusion criteria. According to the SVGE (Spain's Influenza Surveillance System), those <15 years have the highest incidence of influenza per 100,000 population (cumulative-mean rate: 9457.9) compared to those ≥15 years (2285.6), and percentage of admission to the Paediatric Intensive Care Unit (PICU) greater than those >65 years (mean: 29.1% vs. 17.5%). Hospitalisation of severe cases per 100,000 population in children aged 0–4 years and those >65 years is similar (median: 20.2 vs. 28.4). Those aged <15 years have a higher incidence rate per 100,000 population (213.3), in contrast to those aged 15–64 years (21.9) and those aged ≥65 years (65.2). In countries with paediatric vaccination programmes (USA, Finland, and UK) the burden of influenza in children is reduced by 40%–74%, whereas 50%-93.5-% of cases presenting to the ED, hospitalised, admitted to PICU, or dying from influenza are unvaccinated. ConclusionsThe burden of paediatric influenza in Spain includes a significant number of hospitalisations and PICU admissions and justifies the vaccination strategy recommended by the WHO since 2012. In countries with this recommendation, the vaccinated paediatric population is better protected against severe forms of influenza and potential benefits for reducing the burden of paediatric influenza in Spain can be extracted from their data.

Carga de gripe en la población pediátrica en España y los beneficios de la vacunación

IntroductionThe burden of influenza in the paediatric population is often underestimated by healthcare professionals and the general population, mainly due to poor perception of its clinical importance at the individual level and its health impact at the healthcare level. The aim of this review was to collect data on the burden of paediatric influenza in Spain and to compare them with data of countries where vaccination strategies for healthy paediatric populations have been implemented. MethodsWe collected data on the burden of paediatric influenza in Spain through a systematic search of literature published between 2016 and 2021 (PRISMA methodology).We conducted a review of reports from the Spanish Influenza Surveillance System (SVGE) (2010-2011 to 2019-2020) and of international reports (from Canada, Finland, USA, and UK) through a systematic (2016-2021) and pragmatic search. Results1,366 articles were obtained from the systematic searches by country; 26 met the inclusion criteria. According to the SVGE (Spain’s Influenza Surveillance System), those < 15 years have the highest incidence of influenza per 100000 population (cumulative-mean rate: 9,457.9) compared to those ≥ 15 years (2,285.6), and percentage of admission to the Paediatric Intensive Care Unit (PICU) greater than those > 65 years (mean: 29.1% vs. 17.5%). Hospitalisation of severe cases per 100,000 population in children aged 0-4 years and those > 65 years is similar (median: 20.2 vs. 28.4). Those aged < 15 years have a higher incidence rate per 100,000 population (213.3), in contrast to those aged 15-64 years (21.9) and those aged ≥ 65 years (65.2). In countries with paediatric vaccination programmes (USA, Finland, and UK) the burden of influenza in children is reduced by 40%-74%, whereas 50%-93.5-% of cases presenting to the ED, hospitalised, admitted to PICU, or dying from influenza are unvaccinated. ConclusionsThe burden of paediatric influenza in Spain includes a significant number of hospitalisations and PICU admissions and justifies the vaccination strategy recommended by the WHO since 2012. In countries with this recommendation, the vaccinated paediatric population is better protected against severe forms of influenza and potential benefits for reducing the burden of paediatric influenza in Spain can be extracted from their data.

Estimating the burden of seasonal influenza in Spain from surveillance of mild and severe influenza disease, 2010-2016.

BackgroundEstimating the national burden of influenza disease is challenging. We aimed to estimate the disease burden of seasonal influenza in Spain, at the primary care and hospital level, over the 6 influenza seasons after 2009 pandemic.MethodsWe used data from the Spanish Influenza Sentinel Surveillance System to estimate weekly influenza rates and the number of influenza‐like illness (ILI) and mild confirmed influenza cases (MCIC). From the surveillance of severe hospitalized confirmed influenza cases (SHCIC), we obtained hospitalization rates and total number of SHCIC, intensive care unit (ICU) admissions and deaths in influenza hospitalized patients. We estimated both mild and severe influenza cases, overall, and by age‐group (<5, 5‐14, 15‐64, and ≥65 years).ResultsThe highest cumulative rates of MCIC were observed in <15 years (1395‐3155 cases/100 000 population in 5‐14 years) and the lowest in ≥65 years (141‐608 cases/100 000 population). SHCIC rates revealed a characteristic U‐shaped distribution, with annual average hospitalization rates of 16.5 and 18.9 SHCIC/100, 000 p in 0‐4 years, and ≥65 years, respectively. We estimated an annual average of 866 868 cases of ILI attended in primary care (55% were MCIC), 3616 SHCIC, 1232 ICU admissions, and 437 deaths in SHCIC. The percentage of ICU admission among SHCIC was highest at 15‐64 years (42%), while the hospitalization fatality rate ranged from 1% in 0‐4 years to 18% in ≥65 years.ConclusionsThe ongoing Spanish Influenza Surveillance System allowed obtaining crucial information regarding the impact of mild and severe influenza in Spain.

Vigilancia del virus respiratorio sincitial en el marco del Sistema de Vigilancia de la Gripe en España, 2006-2014

IntroductionThe aim of the study is to analyze the information on respiratory syncytial virus (RSV) obtained through the Spanish Influenza Surveillance System (SISS) and to study its usefulness as supplementary information for the characterization of influenza epidemics. MethodsThe temporal patterns of both RSV and influenza viruses were analyzed by patterns comparing the weekly viral detection rates from 2006 to 2014. ResultsIn general, the RSV circulation was characterized by showing a peak between 52-1 weeks, and circulated from 2 to 8weeks before/prior to influenza viruses. ConclusionRSV information obtained from the SISS is useful for the characterization of influenza epidemics in Spain.

Higher vaccine effectiveness in seasons with predominant circulation of seasonal influenza A(H1N1) than in A(H3N2) seasons: Test-negative case-control studies using surveillance data, Spain, 2003-2011

BackgroundWe used data provided by the Spanish influenza surveillance system to measure seasonal influenza vaccine effectiveness (VE) against medically attended cases, laboratory confirmed with the predominately circulating influenza virus over eight seasons (2003–2011). MethodsUsing the test-negative case-control design, we compared the vaccination status of swabbed influenza-like illnesses (ILI) patients who were laboratory confirmed with predominantly circulating influenza strain in the season (cases) to that of ILI patients testing negative for any influenza (controls). Data on age, sex, vaccination status and laboratory results were available for all seasons. We used logistic regression to calculate adjusted influenza VE for age, week of swabbing, Spanish region and season. We calculated the influenza VE by each season and pooling the seasons with the same predominant type/subtype. ResultsOverall influenza VE against infection with A(H3N2) subtype (four seasons) was 31 (95% confidence interval (CI):10; 48). For seasonal influenza A(H1N1) (two seasons), the effectiveness was 86% (95% CI: 65; 94). Against B infection (three seasons), influenza VE was 47% (95% CI: 27; 62). ConclusionsThe Spanish influenza surveillance system allowed estimating influenza VE in the studied seasons for the predominant strain. Strengthening the influenza surveillance will result in more precise VE estimates for decision making.

Geographical spread of influenza incidence in Spain during the 2009 A(H1N1) pandemic wave and the two succeeding influenza seasons.

The aim of this study was to monitor the spatio-temporal spread of influenza incidence in Spain during the 2009 pandemic and the following two influenza seasons 2010-2011 and 2011-2012 using a Bayesian Poisson mixed regression model; and implement this model of geographical analysis in the Spanish Influenza Surveillance System to obtain maps of influenza incidence for every week. In the pandemic wave the maps showed influenza activity spreading from west to east. The 2010-2011 influenza epidemic wave plotted a north-west/south-east pattern of spread. During the 2011-2012 season the spread of influenza was geographically heterogeneous. The most important source of variability in the model is the temporal term. The model of spatio-temporal spread of influenza incidence is a supplementary tool of influenza surveillance in Spain.

Epidemiology of the 2009 influenza pandemic in Spain. The Spanish Influenza Surveillance System

In accordance with European Centre for Disease Prevention and Control recommendations, the Spanish Influenza Surveillance System (SISS) maintained its activity during the summer of 2009, and since July 2009 the pandemic virus activity was monitored by the SISS. In this paper, we describe the epidemiological and virological characteristics of the 2009 pandemic in the Spain through the SISS.Spain experienced a transmission of the new A(H1N1)pdm09 influenza virus during the summer of 2009, which gradually increased, resulting in the pandemic wave in early autumn of that year. The reproductive number R0, estimated during the growth phase of the pandemic wave (1.32; 95% confidence interval [95%CI], 1.29–1.36), showed a transmissibility comparable to preceding pandemics. There was an almost complete replacement of the previous seasonal A(H1N1) influenza virus by the pandemic virus A(H1N1)pdm09.The pandemic virus produced a greater burden of illness than seasonal influenza in children younger than 15 years old, while the incidence in those older than 64 years was lower compared with previous inter-pandemic seasons. Nevertheless, in Spain the 2009 pandemic was characterized as mild, considering the duration of the pandemic period and the influenza detection rate, both in the range of those observed in previous inter-pandemic seasons. Also, the case fatality ratio (CFR) was estimated at 0.58 deaths/1,000 confirmed ILI cases (95%CI, 0.52–0.64), in the range of the two previous pandemics of 1957 and 1968, with the highest CFR observed in the older than 64 years age group. In the 2009 pandemic there was a higher percentage of pandemic confirmed deaths in the younger ages, compared to seasonal influenza, since only 28% of the reported deaths occurred in persons aged 64 years and older.

Genetic diversity of influenza A(H1N1)2009 virus circulating during the season 2010–2011 in Spain

BackgroundGenetic diversity of influenza A(H1N1)2009 viruses has been reported since the pandemic virus emerged in April 2009. Different genetic clades have been identified and defined based on amino acid substitutions found in the haemagglutinin (HA) protein sequences. In Spain, circulating influenza viruses are monitored each season by the regional laboratories enrolled in the Spanish Influenza Surveillance System (SISS). The analysis of the HA gene sequence helps to detect the genetic diversity and viral evolution. ObjectivesTo perform an analysis of the genetic diversity of influenza A(H1N1)2009 viruses circulating in Spain during the season 2010–2011 based on analysis of the HA sequence gene. Study designPhylogenetic analysis based on the HA1 subunit of the haemagglutinin gene was carried out on 220 influenza A(H1N1)2009 viruses circulating during the season 2010–2011. ResultsSix different genetic groups were identified among circulating A(H1N1)2009 viruses, five of them were previously reported during season 2010–2011. A new group, characterized by E172K and K308E changes and a proline at position 83, was observed in 12.27% of the Spanish viruses. ConclusionCo-circulation of six different genetic groups of influenza A(H1N1)2009 viruses was identified in Spain during the season 2010–2011. Nevertheless, at this stage, none of the groups identified to date have resulted in significant antigenic changes according to data collected by World Health Organization Collaborating Centres for influenza surveillance.

Oseltamivir-resistant pandemic influenza a (H1N1) 2009 viruses in Spain

BackgroundPandemic influenza A (H1N1) 2009 virus appeared in Spain on April 25, 2009 for the first time. This new virus was adamantane-resistant but it was sensitive to neuraminidase (NA) inhibitors oseltamivir and zanamivir. ObjectivesTo detect oseltamivir-resistant pandemic influenza A (H1N1) 2009 viruses by the Spanish Influenza Surveillance System (SISS) and a possible spread of oseltamivir-resistant viruses in Spain since starting of the pandemic situation. Study designA total of 1229 respiratory samples taken from 413 severe and 766 non-severe patients with confirmed viral detection of pandemic influenza A (H1N1) 2009 viruses from different Spanish regions were analyzed for the specific detection of the H275Y mutation in NA between April 2009 and May 2010. ResultsH275Y NA substitution was found in 8 patients infected with pandemic influenza A (H1N1) 2009 viruses collected in November and December 2009 and in January 2010. All oseltamivir-resistant viruses were detected in severe patients (8/413, 1.93%) who previously received treatment with oseltamivir. Six of these patients were immunocompromised. ConclusionIn Spain, the number of oseltamivir-resistant pandemic influenza A (H1N1) 2009 viruses is until now very low. No evidence for any spread of oseltamivir-resistant H1N1 viruses is achieved in our Country.

Transmisibilidad y gravedad de la pandemia de gripe A(H1N1)2009 en España

Objectives To estimate the value of the basic reproduction number for the pandemic wave of influenza A (H1N1) 2009 in Spain and to assess its impact on morbidity and mortality in the Spanish population compared with those in the previous influenza season. Methods Data on the incidence of influenza and viral detections were obtained from the Spanish Influenza Surveillance System. Deaths from pandemic influenza were obtained from the Coordinating Center for Health Alerts and Emergencies of the Spanish Ministry of Health and Social Policy, and deaths from seasonal influenza during the period 2003-2008 were obtained from the National Statistics Institute. The reproduction number was estimated by two methods: firstly, by using the growth rate of the cumulative incidence of influenza during the exponential growth phase of the pandemic wave, and secondly (maximum likelihood estimation), through analysis the dates of onset of symptoms observed in pairs of cases based on generation time distribution. We calculated the fatality rate and mortality from influenza by comparing potential years of life lost in the pandemic season with those in previous interpandemic seasons. Results The start of the pandemic wave occurred in Spain earlier in week 40/2009 (from 4 to 10 October), with an absolute predominance of the new strain in the pattern of circulating viruses. The value of R 0 in the growth phase of the wave was 1.29 (95% CI: 1.25-1.33), estimated with the first method, and was 1.01 (95% CI: 0.99-1.03) with the second method. During the pandemic season, there were 318 deaths from pandemic influenza, affecting younger age groups than in previous interpandemic seasons. Consequently, the number of potential years of life lost in the pandemic season (11,612) was estimated at six times the adjusted annual average of the interpandemic influenza seasons for comparison (1,802). Conclusions The estimates of R 0 for the growth phase of the pandemic wave were in the lower range of estimates of this parameter in previous pandemics. Mortality indicators calculated in the pandemic period showed an increase in deaths compared with previous interpandemic seasons, which was most pronounced in young patients.

Influenza pandemic (H1N1) 2009 activity during summer 2009. Effectiveness of the 2008-9 trivalent vaccine against pandemic influenza in Spain

Introduction The Spanish influenza surveillance system (SISS) maintained its activity during the summer of 2009 to monitor the influenza pandemic. Objectives To describe pandemic influenza activity from May to September 2009 and to estimate the effectiveness of the 2008-9 seasonal influenza vaccine against laboratory-confirmed pandemic (H1N1) 2009 influenza. Methods Data from the SISS were used to identify the trend of pandemic (H1N1) 2009 influenza outside the influenza season. For the effectiveness study, we compared the vaccination status of notified cases [influenza-like illnesses (ILI) laboratory confirmed as pandemic influenza] with that of the test-negative controls. Results The first laboratory-confirmed case of the pandemic virus was notified in the system in week 20/2009. The ILI rate increased gradually in the study period, exceeding basic activity in week 38. The proportion of pandemic (H1N1) 2009 influenza viruses detected by the system represented 14% in week 20/2009 and rapidly increased to 90% in week 34. The adjusted vaccine effectiveness of the 2008-9 seasonal vaccine against laboratory-confirmed pandemic influenza was 12% (-30; 41). Conclusions The SISS became an essential tool for pandemic monitoring in Spain. The improved SISS will provide more accurate information on influenza activity in future seasonal or pandemic waves. Using surveillance data, we could not demonstrate the effectiveness of the seasonal 2008-9 vaccine against laboratory-confirmed pandemic influenza.

Vigilancia de la pandemia de gripe (H1N1) 2009 en España

During the summer of 2009, Spain experienced the circulation of the novel influenza (H1N1)2009 virus, beyond the usual period of influenza activity, increasingly evolving up to the presentation in the early autumn of the first wave of the pandemic virus. The objectives of this study are to describe the evolution of the pandemic wave in our country and to assess their impact on morbidity and mortality of the Spanish population. From the information obtained from the Spanish Influenza Surveillance System and the Coordinating Centre for Health Alerts and Emergencies within Spanish Ministry of Health and Social Policy have been estimated a number of epidemiological and virological indicators that were used to assess the level of activity and intensity of the pandemic wave, as well as its severity The beginning of the pandemic wave in Spain started in early autumn 2009 reaching the maximum weekly incidence rate of 372.15 cases/100,000 inhabitants. The highest incidence was registered in under 15 years old. Viral detection rate registered during the pandemic period remained at the range of previously recorded (46.4%). We estimated an overall mortality rate of 0.43 deaths per 1,000 pandemic cases. The 64% of deaths from pandemic influenza occurred in young adults and the highest mortality rates were registered in the 45-64 years age group with 9.35 deaths/1,000,000 inhabitants. Mortality associated with seasonal influenza in the period 2001-2008 was highest in those over 64 years (95% of all deaths). The influenza (H1N1)2009 pandemic wave in Spain showed an early presentation and a medium level of influenza intensity compared to the previous thirteen seasonal influenza waves. Considering lethality or mortality rates, this first pandemic wave was also characterized by a mild severity, although a high percentage of deaths confirmed by the new virus were observed in population under 65 years.

Gripe pandémica H1N1 (2009): experiencia de la Red de Laboratorios de Gripe del Sistema de Vigilancia de la Gripe en España (SVGE)

There are three types of influenza viruses: A, B, C. These viruses evolves constantly due to two main characteristics: the first one is the lack of the correction ability of the viral polymerase which causes the accumulation of single nucleotide mutations in the viral genes introduced by an error-prone viral RNA polymerase, (antigenic shift). The second one is the nature of their genome, formed by eight segments, which allows the interchange of genes between two different viral strains (antigenic drift). This viral plasticity, has allowed to the influenza A viruses to infect new host species and to cause infections with a pandemic characteristics. The Spanish influenza surveillance system, SVGE (its Spanish acronym), arises as a response to the possibility of facing a pandemic situation, especially after the transmission of avian influenza viruses to humans. This surveillance system is formed by sixteen physician and paediatrics network, nineteen epidemiological services coordinated by the National Epidemiological Centre (CNE) and eighteen laboratories , the Spanish Laboratories of Influenza network (ReLEG), coordinated by the National Centre of Microbiology. The aim of this article is to show the action of the ReLEG, in the pandemic caused by the influenza virus A(H1N1) during the season 2009-2010. The main objective of this network is the surveillance of the circulating viruses by means of their detection and their subsequent antigenic and genetic characterization, including the detection of resistance mutations against the main drugs, such as Oseltamivir.