Influenza B lineage circulation and hospitalization rates in a subtropical city, Hong Kong, 2000-2010.
BACKGROUND
A need for quadrivalent vaccines to cover both lineages of influenza B has been raised. Information on the circulation status of influenza B lineages and the associated hospitalization rates is important to assist evidence-based decision making. This retrospective study revealed the situation in a subtropical city over a 10-year period.


METHODS
Sequences of 268 influenza B isolates were analyzed to identify the circulating pool of virus lineages for each year. Hospital records and population census data were used to estimate annual age-specific hospitalization rates.


RESULTS
Cocirculation with 2 influenza B lineages was found in 9 of the 10 years. Only in 6 of the 10 years had the vaccine strain successfully matched with the lineage that was found in >50% of the circulating pool. Six years were predominated by one lineage (occupying >80% of the circulating pool), and these years had higher (average, 1.4-fold) hospitalization rates. Matching between vaccine and circulating lineage was achieved only in 2 of the 6 "predominated years." The Yamagata lineage accounted for most (5/6) of the predominated years. Overall, 24% of influenza admissions were due to influenza B, and influenza B contributed to a higher proportion (41.9%) among children and young teenagers (5-14 years old).


CONCLUSIONS
Cocirculation with 2 influenza B lineages is common in the subtropical region. To predict the next predominant lineage proves to be difficult. Influenza B accounts for a substantial fraction of influenza-associated hospitalizations, especially among children and young teenagers. Quadrivalent vaccines may improve the effectiveness of influenza vaccination programs.
Department of Microbiology, Faculty of Medicine, The Chinese University of Hong Kong, 1/F Clinical Sciences Bldg, Prince of Wales Hospital, Shatin, New Territories, Hong Kong SpecialAdministrative Region, People’s Republic of China. paulkschan@cuhk.edu.hk
Paul K S
PK
Chan
Martin C W
MC
Chan
Jo L K
JL
Cheung
Nelson
N
Lee
Ting F
TF
Leung
Apple C M
AC
Yeung
Martin C S
MC
Wong
Karry L K
KL
Ngai
E Anthony S
EA
Nelson
David S C
DS
Hui
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D005814:Genes, Viral; D019267:Hemagglutinin Glycoproteins, Influenza Virus / Q000235:genetics; D006723:Hong Kong / Q000453:epidemiology; D006760:Hospitalization / Q000706:statistics & numerical data*; D006801:Humans; D007223:Infant; D009981:Influenza B virus / Q000145:classification / Q000235:genetics* / Q000302:isolation & purification*; D007252:Influenza Vaccines / Q000008:administration & dosage; D007251:Influenza, Human / Q000453:epidemiology* / Q000517:prevention & control; D008875:Middle Aged; D010802:Phylogeny; D012367:RNA, Viral / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D012189:Retrospective Studies; D017422:Sequence Analysis, DNA; D014611:Vaccination / Q000379:methods; D055815:Young Adult
D019267:Hemagglutinin Glycoproteins, Influenza Virus; D007252:Influenza Vaccines; D012367:RNA, Viral