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Bull World Health Organ. 2014 May 1;92(5):318-30. doi: 10.2471/BLT.13.124412. Epub 2014 Feb 24.

Influenza seasonality and vaccination timing in tropical and subtropical areas of southern and south-eastern Asia.

Author information

  • 1Center for Disease Control and Prevention, Influenza Programme, c/o US Embassy, Shanti Path, Chanakyapuri, New Delhi, India .
  • 2National Institute of Virology, Pune, India .
  • 3International Centre for Diarrhoeal Disease Research Bangladesh, Dhaka, Bangladesh .
  • 4Institute of Epidemiology, Disease Control and Research, Dhaka, Bangladesh .
  • 5National Institute of Health, Ministry of Public Health, Nonthaburi, Thailand .
  • 6Center for Disease Control and Prevention, Influenza Programme, Nonthaburi, Thailand .
  • 7Ministry of Health, Jakarta, Indonesia .
  • 8Center for Disease Control and Prevention, Jakarta, Indonesia .
  • 9Ministry of Health, Vientiane, Lao People's Democratic Republic.
  • 10Center for Disease Control and Prevention, Influenza Programme, Vientiane, Lao People's Democratic Republic.
  • 11Ministry of Health, Phnom Penh, Cambodia .
  • 12Pasteur Institute, Phnom Penh, Cambodia .
  • 13World Health Organization, Phnom Penh, Cambodia .
  • 14Center for Disease Control and Prevention, Influenza Programme, Phnom Penh, Cambodia .
  • 15National Institute of Hygiene and Epidemiology, Hanoi, Viet Nam .
  • 16Ministry of Health, Singapore .
  • 17Ministry of Health, Kuala Lumpur, Malaysia .
  • 18National Public Health Laboratory, Kuala Lumpur, Malaysia .
  • 19Institute of Medical Research, Kuala Lumpur, Malaysia .
  • 20Research Institute for Tropical Medicine, Alabang, Philippines .
  • 21Department of Health, Manila, Philippines .
  • 22Centers for Disease Control and Prevention, Atlanta, United States of America .
  • 23Center for Disease Control and Prevention, Influenza Programme, Hanoi, Viet Nam .


in English, Arabic, Chinese, French, Russian, Spanish


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.


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.


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.


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.

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