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      Influenza seasonality and vaccination timing in tropical and subtropical areas of southern and south-eastern Asia Translated title: C????????? ?????? ? ????? ?????????? ? ??????????? ? ?????????????? ??????? ????? ? ???-????????? ???? Translated title: Saisonnalité de la grippe et calendrier de vaccination dans les zones tropicales et subtropicales de l'Asie du Sud et de l'Asie du Sud-Est Translated title: موسمية الأنفلونزا وتوقيت تطعيمها في المناطق المدارية ودون المدارية في جنوب وجنوب شرق آسيا Translated title: ?????????????????????????? Translated title: La estacionalidad de la gripe y la fecha de vacunación en áreas tropicales y subtropicales del sur y sureste de Asia

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      1 , 2 , 3 , 4 , 3 , 5 , 5 , 6 , 7 , 7 , 7 , 8 , 9 , 9 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 15 , 16 , 16 , 17 , 18 , 19 , 20 , 21 , 2 , 22 , 22 , 23 , 3
      Bulletin of the World Health Organization
      World Health Organization

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          Abstract

          Objective To characterize influenza seasonality and identify the best time of the year for vaccination against influenza in tropical and subtropical countries of southern and south-eastern Asia that lie north of the equator. Methods Weekly influenza surveillance data for 2006 to 2011 were obtained from Bangladesh, Cambodia, India, Indonesia, the Lao People's Democratic Republic, Malaysia, the Philippines, Singapore, Thailand and Viet Nam. Weekly rates of influenza activity were based on the percentage of all nasopharyngeal samples collected during the year that tested positive for influenza virus or viral nucleic acid on any given week. Monthly positivity rates were then calculated to define annual peaks of influenza activity in each country and across countries. Findings Influenza activity peaked between June/July and October in seven countries, three of which showed a second peak in December to February. Countries closer to the equator had year-round circulation without discrete peaks. Viral types and subtypes varied from year to year but not across countries in a given year. The cumulative proportion of specimens that tested positive from June to November was > 60% in Bangladesh, Cambodia, India, the Lao People's Democratic Republic, the Philippines, Thailand and Viet Nam. Thus, these tropical and subtropical countries exhibited earlier influenza activity peaks than temperate climate countries north of the equator. Conclusion Most southern and south-eastern Asian countries lying north of the equator should consider vaccinating against influenza from April to June; countries near the equator without a distinct peak in influenza activity can base vaccination timing on local factors.

          Translated abstract

          Résumé Objectif Caractériser la saisonnalité de la grippe et identifier le meilleur moment de l'année pour la vaccination contre la grippe dans les pays tropicaux et subtropicaux de l'Asie du Sud et de l'Asie du Sud-Est, qui sont situés au nord de l'équateur. Méthodes Les données hebdomadaires de la surveillance de la grippe pour la période allant de 2006 à 2001 ont été obtenues auprès du Bangladesh, du Cambodge, de l'Inde, de la République démocratique populaire lao, de la Malaisie, des Philippines, de Singapour, de la Thaïlande et du Viet Nam. Les taux hebdomadaires de l'activité grippale étaient basés sur le pourcentage de tous les échantillons nasopharyngés collectés au cours de l'année et dont les tests étaient positifs au virus de la grippe ou à l'acide nucléique viral au cours d'une semaine donnée. Les pourcentages de cas positifs mensuels ont été ensuite calculés pour définir les pics annuels de l'activité grippale au sein de chaque pays et entre les pays. Résultats L'activité grippale atteint son pic entre les mois de juin/juillet et octobre dans sept pays, parmi lesquels trois pays ont présenté un second pic entre les mois de décembre et février. Les pays proches de l'équateur présentent une circulation continue sans pic distinct. Les types et sous-types viraux varient d'une année à l'autre, mais pas entre les pays au cours d'une année donnée. Le pourcentage cumulatif des prélèvements dont les tests étaient positifs de juin à novembre, était supérieur à 60% au Bangladesh, au Cambodge, en Inde, en République démocratique populaire lao, aux Philippines, en Thaïlande et au Viet Nam. Par conséquent, ces pays tropicaux et subtropicaux ont enregistré plus tôt des pics d'activité grippale que dans les pays à climat tempéré situés au nord de l'équateur. Conclusion La plupart des pays de l'Asie du Sud et de l'Asie du Sud-Est, situés au nord de l'équateur, devraient envisager la vaccination contre la grippe pendant la période allant d'avril à juin. Les pays proches de l'équateur sans pic distinct d'activité grippale peuvent baser leur calendrier de vaccination sur leurs facteurs locaux.

          Translated abstract

          Resumen Objetivo Describir la estacionalidad de la gripe e identificar el mejor momento del año para llevar a cabo la vacunación contra la gripe en países tropicales y subtropicales del sur y sureste de Asia situados al norte del ecuador. Métodos Se obtuvieron los datos semanales de vigilancia de la gripe de los años 2006 a 2011 de Bangladesh, Camboya, India, Indonesia, la República Democrática Popular Lao, Malasia, Filipinas, Singapur, Tailandia y Viet Nam. Las tasas semanales de la actividad de la gripe se basaron en el porcentaje de todas las muestras nasofaríngeas recogidas durante el año que dieron positivo en la prueba del virus de la gripe o del ácido nucleido viral en cualquier semana. Los índices de resultados positivos mensuales se calcularon luego a fin de determinar los picos anuales de la actividad de la gripe en cada uno de los países y entre países. Resultados La actividad de la gripe experimentó un aumento entre junio y julio, y octubre en siete países, tres de los cuales mostraron un segundo pico de actividad de diciembre a febrero. Los países más cercanos al ecuador presentaron una circulación durante todo el año sin picos discontinuos. Los tipos y subtipos virales variaron de año en año, pero no entre los países en un año determinado. La proporción acumulada de individuos que dieron positivo de junio a noviembre fue > 60 % en Bangladesh, Camboya, India, la República Democrática Popular Lao, Filipinas, Tailandia y Viet Nam. Así, en estos países tropicales y subtropicales, los picos de actividad de la gripe se produjeron antes que en los países de clima templado al norte de la línea ecuatorial. Conclusión La mayoría de los países del sur y sureste asiático situados al norte del ecuador deberían considerar llevar a cabo la vacunación contra la gripe de abril a junio; mientras que los países cercanos al ecuador sin picos marcados en la actividad de la gripe pueden basar la fecha de vacunación en factores locales.

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          Efficacy and effectiveness of influenza vaccines: a systematic review and meta-analysis

          The Lancet Infectious Diseases, 12(1), 36-44
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            Global Influenza Seasonality: Reconciling Patterns across Temperate and Tropical Regions

            Background Despite the significant disease burden of the influenza virus in humans, our understanding of the basis for its pronounced seasonality remains incomplete. Past observations that influenza epidemics occur in the winter across temperate climates, combined with insufficient knowledge about the epidemiology of influenza in the tropics, led to the perception that cool and dry conditions were a necessary, and possibly sufficient, driver of influenza epidemics. Recent reports of substantial levels of influenza virus activity and well-defined seasonality in tropical regions, where warm and humid conditions often persist year-round, have rendered previous hypotheses insufficient for explaining global patterns of influenza. Objective In this review, we examined the scientific evidence for the seasonal mechanisms that potentially explain the complex seasonal patterns of influenza disease activity observed globally. Methods In this review we assessed the strength of a range of hypotheses that attempt to explain observations of influenza seasonality across different latitudes and how they relate to each other. We reviewed studies describing population-scale observations, mathematical models, and ecological, laboratory, and clinical experiments pertaining to influenza seasonality. The literature review includes studies that directly mention the topic of influenza seasonality, as well as other topics we believed to be relevant. We also developed an analytical framework that highlights the complex interactions among environmental stimuli, mediating mechanisms, and the seasonal timing of influenza epidemics and identify critical areas for further research. Conclusions The central questions in influenza seasonality remain unresolved. Future research is particularly needed in tropical localities, where our understanding of seasonality remains poor, and will require a combination of experimental and observational studies. Further understanding of the environmental factors that drive influenza circulation also may be useful to predict how dynamics will be affected at regional levels by global climate change.
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              Absolute humidity modulates influenza survival, transmission, and seasonality.

              Influenza A incidence peaks during winter in temperate regions. The basis for this pronounced seasonality is not understood, nor is it well documented how influenza A transmission principally occurs. Previous studies indicate that relative humidity (RH) affects both influenza virus transmission (IVT) and influenza virus survival (IVS). Here, we reanalyze these data to explore the effects of absolute humidity on IVT and IVS. We find that absolute humidity (AH) constrains both transmission efficiency and IVS much more significantly than RH. In the studies presented, 50% of IVT variability and 90% of IVS variability are explained by AH, whereas, respectively, only 12% and 36% are explained by RH. In temperate regions, both outdoor and indoor AH possess a strong seasonal cycle that minimizes in winter. This seasonal cycle is consistent with a wintertime increase in IVS and IVT and may explain the seasonality of influenza. Thus, differences in AH provide a single, coherent, more physically sound explanation for the observed variability of IVS, IVT and influenza seasonality in temperate regions. This hypothesis can be further tested through future, additional laboratory, epidemiological and modeling studies.
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                Author and article information

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                Journal
                bwho
                Bulletin of the World Health Organization
                Bull World Health Organ
                World Health Organization (Genebra )
                0042-9686
                May 2014
                : 92
                : 5
                : 318-330
                Affiliations
                [1 ] Center for Disease Control and Prevention Peoples R China
                [2 ] National Institute of Virology South Africa
                [3 ] International Centre for Diarrhoeal Disease Research Bangladesh Bangladesh
                [4 ] Institute of Epidemiology, Disease Control and Research Bangladesh
                [5 ] National Institute of Health Colombia
                [6 ] Center for Disease Control and Prevention Peoples R China
                [7 ] Ministry of Health Jamaica
                [8 ] Center for Disease Control and Prevention Peoples R China
                [9 ] Ministry of Health, Vientiane Lao People?s Democratic Republic
                [10 ] Center for Disease Control and Prevention Peoples R China
                [11 ] Ministry of Health Jamaica
                [12 ] Pasteur Institute Belgium
                [13 ] World Health Organization Switzerland
                [14 ] Center for Disease Control and Prevention Peoples R China
                [15 ] National Institute of Hygiene and Epidemiology Vietnam
                [16 ] Ministry of Health Jamaica
                [17 ] Ministry of Health Jamaica
                [18 ] National Public Health Laboratory Malaysia
                [19 ] Institute of Medical Research Brazil
                [20 ] Research Institute for Tropical Medicine Philippines
                [21 ] Department of Health Philippines
                [22 ] Centers for Disease Control and Prevention USA
                [23 ] Center for Disease Control and Prevention Peoples R China
                Article
                S0042-96862014000500318
                10.2471/BLT.13.124412
                4007122
                24839321
                c6701a72-5fe3-450a-a308-8c8918ba05fb

                http://creativecommons.org/licenses/by/4.0/

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                Self URI (journal page): http://www.scielosp.org/scielo.php?script=sci_serial&pid=0042-9686&lng=en
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