The 2009 influenza A (H1N1) pandemic. Management and vaccination strategies in The Netherlands

Abstract

Prior to 2009, The Netherlands had prepared itself extensively for a potential pandemic. Multidisciplinary guidelines had been drafted to control transmission and limit adverse outcomes for both a phase of early incidental introduction and for a phase with widespread transmission. The Ministry of Health had ensured a supply and distribution schedule for antivirals and negotiated a contract for vaccine purchases. During the pandemic, existing surveillance was expanded, the established infectious disease response structure was activated, and the previously prepared protocols for communication, diagnostics, use of antivirals, and vaccination implementation were operationalized and implemented. When the pandemic turned out to be less severe than many had anticipated, risk communication and rapid modification of guidelines and communication became a major challenge. Antivirals and pandemic vaccines were reserved for those at high risk for severe outcomes only. Overall, the impact of the pandemic was comparable to the impact of an average seasonal influenza epidemic, but with a shift in (severe) outcomes from the very young and elderly toward young adults. Established prepared protocols enabled timely coordinated responses. In preparing for the worst, sufficient attention must be given to preparing for a mild scenario as well.

Fig. 1

Weekly incidence of influenza-like illness (ILI) in 2008 and 2009. ILI incidence in GP practices per 10,000 people in 2008 (light blue line) and 2009 (dark blue line). Weekly incidence of pneumonia per 10,000 people in GP practices (black line, 2009; gray line, 2008)

Fig. 2

Final epidemic overview of notified hospitalizations due to confirmed influenza A(H1N1)pdm in The Netherlands in time (a numbers by week) and place (b incidence by province). Epidemic overview. a Number of notified influenza A(H1N1)pdm hospitalization per week: x-axis, weeks of the year; y-axis, number of notified influenza A(H1N1)pdm hospitalization. b 2009 incidence of influenza A(H1N1)pdm hospitalizations by province: ranging from 1–5/100,000 (lightest color code) to > 25/100,000 (darkest color). Light blue: laboratory confirmation missing

Fig. 3

Epidemic impact differs by age: a hospitalizations; b ICU admissions; and c deaths (all by age). Changing severity with age. a Number of notified influenza A(H1N1)pdm hospitalizations in 2009 by age group: x-axis, age categories; y-axis, number of notified influenza A(H1N1)pdm hospitalization. b Number of notified intensive care (IC) influenza A(H1N1)pdm admissions in 2009 by age group: x-axis, age categories; y-axis, number of notified influenza A(H1N1)pdm IC admissions. c Number of notified influenza A(H1N1)pdm deaths in 2009 by age group: x-axis, age categories; y-axis, number of notified influenza A(H1N1)pdm deaths. Light blue: laboratory confirmation missing