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


RESULTS
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.


CONCLUSIONS
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.
Center for Disease Control and Prevention, Influenza Programme, c/o US Embassy, Shanti Path, Chanakyapuri, New Delhi, India .
Siddhartha
S
Saha
National Institute of Virology, Pune, India .
Mandeep
M
Chadha
International Centre for Diarrhoeal Disease Research Bangladesh, Dhaka, Bangladesh .
Abdullah
A
Al Mamun
Institute of Epidemiology, Disease Control and Research, Dhaka, Bangladesh .
Mahmudur
M
Rahman
International Centre for Diarrhoeal Disease Research Bangladesh, Dhaka, Bangladesh .
Katharine
K
Sturm-Ramirez
National Institute of Health, Ministry of Public Health, Nonthaburi, Thailand .
Malinee
M
Chittaganpitch
National Institute of Health, Ministry of Public Health, Nonthaburi, Thailand .
Sirima
S
Pattamadilok
Center for Disease Control and Prevention, Influenza Programme, Nonthaburi, Thailand .
Sonja J
SJ
Olsen
Ministry of Health, Jakarta, Indonesia .
Ondri Dwi
OD
Sampurno
Ministry of Health, Jakarta, Indonesia .
Vivi
V
Setiawaty
Ministry of Health, Jakarta, Indonesia .
Krisna Nur Andriana
KN
Pangesti
Center for Disease Control and Prevention, Jakarta, Indonesia .
Gina
G
Samaan
Ministry of Health, Vientiane, Lao People's Democratic Republic.
Sibounhom
S
Archkhawongs
Ministry of Health, Vientiane, Lao People's Democratic Republic.
Phengta
P
Vongphrachanh
Ministry of Health, Vientiane, Lao People's Democratic Republic.
Darouny
D
Phonekeo
Center for Disease Control and Prevention, Influenza Programme, Vientiane, Lao People's Democratic Republic.
Andrew
A
Corwin
Ministry of Health, Phnom Penh, Cambodia .
Sok
S
Touch
Pasteur Institute, Phnom Penh, Cambodia .
Philippe
P
Buchy
World Health Organization, Phnom Penh, Cambodia .
Nora
N
Chea
Center for Disease Control and Prevention, Influenza Programme, Phnom Penh, Cambodia .
Paul
P
Kitsutani
National Institute of Hygiene and Epidemiology, Hanoi, Viet Nam .
Le Quynh
le Q
Mai
National Institute of Hygiene and Epidemiology, Hanoi, Viet Nam .
Vu Dinh
VD
Thiem
Ministry of Health, Singapore .
Raymond
R
Lin
Ministry of Health, Singapore .
Constance
C
Low
Ministry of Health, Kuala Lumpur, Malaysia .
Chong Chee
CC
Kheong
National Public Health Laboratory, Kuala Lumpur, Malaysia .
Norizah
N
Ismail
Institute of Medical Research, Kuala Lumpur, Malaysia .
Mohd Apandi
MA
Yusof
Research Institute for Tropical Medicine, Alabang, Philippines .
Amado
A
Tandoc
Department of Health, Manila, Philippines .
Vito
V
Roque
National Institute of Virology, Pune, India .
Akhilesh
A
Mishra
Centers for Disease Control and Prevention, Atlanta, United States of America .
Ann C
AC
Moen
Centers for Disease Control and Prevention, Atlanta, United States of America .
Marc-Alain
MA
Widdowson
Center for Disease Control and Prevention, Influenza Programme, Hanoi, Viet Nam .
Jeffrey
J
Partridge
International Centre for Diarrhoeal Disease Research Bangladesh, Dhaka, Bangladesh .
Renu B
RB
Lal
D001210:Asia, Southeastern / Q000453:epidemiology; D006801:Humans; D007252:Influenza Vaccines; D007251:Influenza, Human / Q000453:epidemiology* / Q000517:prevention & control / Q000821:virology*; D009297:Nasal Mucosa / Q000821:virology; D009975:Orthomyxoviridae / Q000276:immunology / Q000302:isolation & purification*; D012621:Seasons; D014329:Tropical Climate
D007252:Influenza Vaccines