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Differences in Influenza Seasonality by Latitude, Northern India - Volume 20, Number 10—October 2014 - Emerging Infectious Disease journal - CDC

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Differences in Influenza Seasonality by Latitude, Northern India - Volume 20, Number 10—October 2014 - Emerging Infectious Disease journal - CDC

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Volume 20, Number 10—October 2014


Differences in Influenza Seasonality by Latitude, Northern India

Parvaiz A. Koul1Comments to Author , Shobha Broor12, Siddhartha Saha, John Barnes, Catherine Smith, Michael Shaw, Mandeep Chadha, and Renu B. Lal
Author affiliations: Sheri-Kashmir Institute of Medical Sciences, Srinagar, India (P.A. Koul)All India Institute of Medical Sciences, New Delhi, India (S. Broor)Centers for Disease Control and Prevention, Atlanta, Georgia, USA (S. Saha, J. Barnes, C. Smith, M. Shaw, R.B. Lal)National Institute of Virology, Pune, India (M. Chadha)


The seasonality of influenza in the tropics complicates vaccination timing. We investigated influenza seasonality in northern India and found influenza positivity peaked in Srinagar (34.09°N) in January–March but peaked in New Delhi (28.66°N) in July–September. Srinagar should consider influenza vaccination in October–November, but New Delhi should vaccinate in May–June.
Annual and pandemic influenza are sources of considerable illness and death worldwide (1). Human influenza infection rates peak during the winter months in temperate regions; however, the pattern of influenza is different in tropical and subtropical areas, with year-round circulation in some areas and biannual peaks in others (25). The complex seasonality of influenza in the tropics complicates appropriate vaccination recommendations, particularly the timing of vaccination campaigns in tropical regions (3,4).
India has discrete seasons that vary greatly from north to south. Jammu and Kashmir, the northernmost state of India, has severe winters from December to March, whereas Delhi, the capital region, has milder winters. Sentinel surveillance for influenza in India has shown distinct influenza peaks in India (68). We undertook influenza surveillance during 2011–2012 in 2 cities in northern India, Srinagar and New Delhi, which are ≈500 km apart, and found evidence for discrete seasonality related to the latitudes of these cities, a finding that has implications for influenza vaccination policy and timing.

Prof Koul heads the Internal and Pulmonary Medicine department in SheriKashmir Institute of Medical Sciences, Srinagar, India. His current research interests include pulmonary disease and respiratory infections, especially influenza and influenza vaccination.


We acknowledge the authors and originating and submitting laboratories of the sequences from the GISAID EpiFlu Database (http://www.gisaid.org) presented in the Technical Appendix.
This study was supported in part by cooperative agreement 5U51IP 000333 from the US Centers for Disease Control and Prevention (Atlanta, GA, USA).


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Technical Appendix

Suggested citation for this article: Koul PA, Broor S, Saha S, Barnes J, Smith C, Shaw M, et al. Differences in influenza seasonality by latitude, northern India. Emerg Infect Dis [Internet]. 2014 Oct [date cited]. http://dx.doi.org/10.3201/eid2010.140431
DOI: 10.3201/eid2010.140431
1These authors contributed equally to this article.
2Current affiliation: INCLEN Foundation, New Delhi, India.

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