Age-Dependent Patterns of Infection and Severity Explaining the Low Impact of 2009 Influenza A (H1N1): Evidence From Serial Serologic Surveys in the Netherlands

• Published in: American journal of epidemiology Vol. 174; no. 11; pp. 1307 - 1315
• Main Authors: Steens, Anneke, Waaijenborg, Sandra, Teunis, Peter F. M., Reimerink, Johan H. J., Meijer, Adam, van der Lubben, Mariken, Koopmans, Marion, van der Sande, Marianne A. B., Wallinga, Jacco, van Boven, Michiel
• Format: Journal Article
• Language: English
• Published: Cary, NC Oxford University Press 01.12.2011; Oxford Publishing Limited (England)
• Subjects: Adolescent; Adult; Age Factors; Aged; Biological and medical sciences; Child; Child, Preschool; Disease transmission; Epidemics; Epidemiology; General aspects; Human viral diseases; Humans; Infant; Infectious diseases; Influenza A Virus, H1N1 Subtype; Influenza, Human - epidemiology; Medical sciences; Medical statistics; Middle Aged; Miscellaneous; Netherlands - epidemiology; Public health; Public health. Hygiene; Public health. Hygiene-occupational medicine; Seroepidemiologic Studies; Swine flu; Viral diseases; Viral diseases of the respiratory system and ent viral diseases; Young Adult; Netherlands; Europe; influenza, human; disease outbreaks; disease transmission, infectious; influenza A virus, H1N1 subtype; serology; infectious; Disease; Transmission; Orthomyxoviridae; Serology; Epidemiology; 2009; disease transmission; Age; Public health; Epidemic; Human; Typing; H1 N1 subtype; Virus; Infection; Survey; Influenzavirus A; Surveillance; Influenza A virus; Viral disease; Influenza; Influenza A (H1N1); Subtype
• ISSN: 0002-9262; 1476-6256
• DOI: 10.1093/aje/kwr245

Despite considerable research efforts in specific subpopulations, reliable estimates of the infection attack rates and severity of 2009 influenza A (H1N1) in the general population remain scarce. Such estimates are essential to the tailoring of future control strategies. Therefore, 2 serial population-based serologic surveys were conducted, before and after the 2009 influenza A (H1N1) epidemic, in the Netherlands. Random age-stratified samples were obtained using a 2-stage cluster design. Participants donated blood and completed a questionnaire. Data on sentinel general practitioner-attended influenza-like illness and nationwide hospitalization and mortality were used to assess the severity of infection. The estimated infection attack rates were low in the general population (7.6%, 95% confidence interval: 3.6, 11) but high in children aged 5-19 years (35%, 95% confidence interval: 25, 45). The estimated hospitalization and mortality rates per infection increased significantly with age (5-19 years: 0.042% and 0.00094%, respectively; 20-39 years: 0.12% and 0.0025%; 40-59 years: 0.68% and 0.032%; 60-75 years: >0.81% and >0.068%). The high infection attack rate in children and the very low attack rate in older adults, together with the low severity of illness per infection in children but substantial severity in older adults, produced an epidemic with a low overall impact.