title: The epidemiology of interpandemic and pandemic influenza in Vietnam, 2007-2010: the Ha Nam household cohort study I.
abstract: Prospective community-based studies have provided fundamental insights into the epidemiology of influenza in temperate regions, but few comparable studies have been undertaken in the tropics. The authors conducted prospective influenza surveillance and intermittent seroprevalence surveys in a household-based cohort in Vietnam between December 2007 and April 2010, resulting in 1,793 person-seasons of influenza surveillance. Age- and sex-standardized estimates of the risk of acquiring any influenza infection per season in persons 5 years of age or older were 21.1% (95% confidence interval: 17.4, 24.7) in season 1, 26.4% (95% confidence interval: 22.6, 30.2) in season 2, and 17.0% (95% confidence interval: 13.6, 20.4) in season 3. Some individuals experienced multiple episodes of infection with different influenza types/subtypes in the same season (n = 27) or reinfection with the same subtype in different seasons (n = 22). The highest risk of influenza infection was in persons 5-9 years old, in whom the risk of influenza infection per season was 41.8%. Although the highest infection risk was in school-aged children, there were important heterogeneities in the age of infection by subtype and season. These heterogeneities could influence the impact of school closure and childhood vaccination on influenza transmission in tropical areas, such as Vietnam.
authors.affiliation: Oxford University Clinical Research Unit, National Hospital of Tropical Diseases, 78 Giai Phong Street, Dong Da District, Hanoi, Vietnam. peter.horby@gmail.com
authors.forename: Peter
authors.initials: P
authors.lastname: Horby
authors.forename: Le Quynh
authors.initials: le Q
authors.lastname: Mai
authors.forename: Annette
authors.initials: A
authors.lastname: Fox
authors.forename: Pham Quang
authors.initials: PQ
authors.lastname: Thai
authors.forename: Nguyen
authors.initials: N
authors.lastname: Thi Thu Yen
authors.forename: Le Thi
authors.initials: le T
authors.lastname: Thanh
authors.forename: Nguyen
authors.initials: N
authors.lastname: Le Khanh Hang
authors.forename: Tran Nhu
authors.initials: TN
authors.lastname: Duong
authors.forename: Dang Dinh
authors.initials: DD
authors.lastname: Thoang
authors.forename: Jeremy
authors.initials: J
authors.lastname: Farrar
authors.forename: Marcel
authors.initials: M
authors.lastname: Wolbers
authors.forename: Nguyen Tran
authors.initials: NT
authors.lastname: Hien
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D015994:Incidence; D007223:Infant; D007231:Infant, Newborn; D053118:Influenza A Virus, H1N1 Subtype / Q000302:isolation & purification*; D007251:Influenza, Human / Q000453:epidemiology*; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D058873:Pandemics; D011159:Population Surveillance; D011446:Prospective Studies; D012367:RNA, Viral / Q000032:analysis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012306:Risk; D016036:Seroepidemiologic Studies; D012737:Sex Factors; D014329:Tropical Climate; D014744:Vietnam / Q000453:epidemiology; D055815:Young Adult
chemical_list: D012367:RNA, Viral