Initial surveillance of 2009 influenza A(H1N1) pandemic in the European Union and European Economic Area, April – September 2009

Abstract

European Union (EU) and European Economic Area (EEA) countries reported surveillance data on 2009 pandemic influenza A(H1N1) cases to the European Centre for Disease Prevention and Control (ECDC) through the Early Warning and Response System (EWRS) during the early phase of the 2009 pandemic. We describe the main epidemiological findings and their implications in respect to the second wave of the 2009 influenza pandemic. Two reporting systems were in place (aggregate and case-based) from June to September 2009 to monitor the evolution of the pandemic. The notification rate was assessed through aggregate reports. Individual data were analysed retrospectively to describe the population affected. The reporting peak of the first wave of the 2009 pandemic influenza was reached in the first week of August. Transmission was travel-related in the early stage and community transmission within EU/EEA countries was reported from June 2009. Seventy eight per cent of affected individuals were less than 30 years old. The proportions of cases with complications and underlying conditions were 3% and 7%, respectively. The most frequent underlying medical conditions were chronic lung (37%) and cardio-vascular diseases (15%). Complication and hospitalisation were both associated with underlying conditions regardless of age. The information from the first wave of the pandemic produced a basis to determine risk groups and vaccination strategies before the start of the winter wave. Public health recommendations should be guided by early capture of profiles of affected populations through monitoring of infectious diseases.

Surveillance trends of the 2009 influenza A(H1N1) pandemic in Europe

“…Overall attack rates estimated by serology were higher than for seasonal influenza, although the pandemic virus affected fewer older persons (65 years and older), who had been exposed to a similar virus circulating in the 1950s and before [16,18]. There is clear evidence that there were many mild or asymptomatic cases in this pandemic, but whether they were more common than in the previously recorded pandemics is impossible to determine because it is only in this pandemic that there has been enough accurate seroepidemiology which combined with case reporting allowed such estimates to be made [7,12,17]. Attack rates were highest in young people, with country reports revealing that the highest rates of infection occurred in school-age children [16,18] and some hospital paediatric services and intensive care services were especially stressed [19].…”

“…When country representatives agreed in week 39 that central collection of case-based data was no longer justified, the database contained 11,275 individual records (11,207 of which were laboratory-confirmed) submitted by 28 countries. A detailed analysis of these first cases is available elsewhere [7].…”

Long-term respiratory follow-up of H1N1 infection

“…The first human infections with the new influenza A (H1N1) virus were confirmed in April 2009 in America, but the infection had been rapidly spreading around the world and in June 2009 World Health Organization (WHO) declared a pandemic [1-5]. WHO had advised countries in the northern hemisphere to prepare for a second wave of pandemic spread [6].…”

Severe acute respiratory infections in the postpandemic era of H1N1

“…A predilection for younger ages with less chronic conditions as risk factors, compared with seasonal influenza, was demonstrated very early, with pregnancy and obesity being the newly recognized vulnerable populations [14,[38][39][40]. A predilection for younger ages with less chronic conditions as risk factors, compared with seasonal influenza, was demonstrated very early, with pregnancy and obesity being the newly recognized vulnerable populations [14,[38][39][40].…”