The epidemiology of interpandemic and pandemic influenza in Vietnam, 2007-2010: the Ha Nam household cohort study I. Horby, P., Mai, L. Q., Fox, A., Thai, P. Q., Thi Thu Yen, N., Thanh, L. T., Le Khanh Hang, N., Duong, T. N., Thoang, D. D., Farrar, J., Wolbers, M., & Hien, N. T. American journal of epidemiology, 175(10):1062–1074, May, 2012.
doi  abstract   bibtex   
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.
@article{horby_epidemiology_2012,
	title = {The epidemiology of interpandemic and pandemic influenza in {Vietnam}, 2007-2010: the {Ha} {Nam} household cohort study {I}.},
	volume = {175},
	issn = {1476-6256 0002-9262},
	doi = {10.1093/aje/kws121},
	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.},
	language = {eng},
	number = {10},
	journal = {American journal of epidemiology},
	author = {Horby, Peter and Mai, Le Quynh and Fox, Annette and Thai, Pham Quang and Thi Thu Yen, Nguyen and Thanh, Le Thi and Le Khanh Hang, Nguyen and Duong, Tran Nhu and Thoang, Dang Dinh and Farrar, Jeremy and Wolbers, Marcel and Hien, Nguyen Tran},
	month = may,
	year = {2012},
	pmid = {22411862},
	pmcid = {PMC3353138},
	keywords = {*Pandemics, Adolescent, Adult, Age Factors, Aged, Child, Child, Preschool, Female, Humans, Incidence, Infant, Infant, Newborn, Influenza A Virus, H1N1 Subtype/*isolation \& purification, Influenza, Human/*epidemiology, Longitudinal Studies, Male, Middle Aged, Population Surveillance, Prospective Studies, RNA, Viral/analysis, Reverse Transcriptase Polymerase Chain Reaction, Risk, Seroepidemiologic Studies, Sex Factors, Tropical Climate, Vietnam/epidemiology, Young Adult},
	pages = {1062--1074},
}

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