The effectiveness of seasonal trivalent inactivated influenza vaccine in preventing laboratory confirmed influenza hospitalisations in Auckland, New Zealand in 2012.
BACKGROUND
Few studies report the effectiveness of trivalent inactivated influenza vaccine (TIV) in preventing hospitalisation for influenza-confirmed respiratory infections. Using a prospective surveillance platform, this study reports the first such estimate from a well-defined ethnically diverse population in New Zealand (NZ).


METHODS
A case test-negative design was used to estimate propensity adjusted vaccine effectiveness. Patients with a severe acute respiratory infection (SARI), defined as a patient of any age requiring hospitalisation with a history of a fever or a measured temperature ≥38°C and cough and onset within the past 7 days, admitted to public hospitals in South and Central Auckland were eligible for inclusion in the study. Cases were SARI patients who tested positive for influenza, while non-cases (controls) were SARI patients who tested negative. Results were adjusted for the propensity to be vaccinated and the timing of the influenza season.


RESULTS
The propensity and season adjusted vaccine effectiveness (VE) was estimated as 39% (95% CI 16;56). The VE point estimate against influenza A (H1N1) was lower than for influenza B or influenza A (H3N2) but confidence intervals were wide and overlapping. Estimated VE was 59% (95% CI 26;77) in patients aged 45-64 years but only 8% (-78;53) in those aged 65 years and above.


CONCLUSIONS
Prospective surveillance for SARI has been successfully established in NZ. This study for the first year, the 2012 influenza season, has shown low to moderate protection by TIV against influenza positive hospitalisation.
The University of Auckland, Private Bag 92019, Victoria St West, Auckland, New Zealand. Electronic address: n.turner@auckland.ac.nz.
Nikki
N
Turner
The University of Otago, PO Box 7343 Wellington South 6242, Wellington, New Zealand. Electronic address: nevil.pierse@otago.ac.nz.
Nevil
N
Pierse
Institute of Environmental Science and Research, PO Box 40-158 Upper Hutt 5140, Wellington, New Zealand. Electronic address: Ange.Bissielo@esr.cri.nz.
Ange
A
Bissielo
Institute of Environmental Science and Research, PO Box 40-158 Upper Hutt 5140, Wellington, New Zealand. Electronic address: Sue.Huang@esr.cri.nz.
Q Sue
QS
Huang
The University of Otago, PO Box 7343 Wellington South 6242, Wellington, New Zealand. Electronic address: michael.baker@otago.ac.nz.
Michael G
MG
Baker
Centers for Disease Control and Prevention, Atlanta, GA 30333, USA. Electronic address: zux5@cdc.gov.
Marc-Alain
MA
Widdowson
The Australian National University, Canberra 0200, ACT, Australia; Victorian Infectious Diseases Reference Laboratory, 10 Wrecklyn St., North Melbourne, 3051 Melbourne, VIC, Australia. Electronic address: Heath.Kelly@mh.org.au.
Heath
H
Kelly
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D005260:Female; D006760:Hospitalization / Q000706:statistics & numerical data; D006801:Humans; D007223:Infant; D053118:Influenza A Virus, H1N1 Subtype; D053122:Influenza A Virus, H3N2 Subtype; D007252:Influenza Vaccines / Q000627:therapeutic use*; D007251:Influenza, Human / Q000453:epidemiology / Q000517:prevention & control*; D008297:Male; D008875:Middle Aged; D009520:New Zealand / Q000453:epidemiology; D018571:Sentinel Surveillance; D015164:Vaccines, Inactivated / Q000627:therapeutic use; D055815:Young Adult
D007252:Influenza Vaccines; D015164:Vaccines, Inactivated; C510903:fluarix
Immunisation; Influenza vaccine; Vaccination; Vaccine effectiveness