Influenza vaccine effectiveness in preventing influenza A(H3N2)-related hospitalizations in adults targeted for vaccination by type of vaccine: a hospital-based test-negative study, 2011-2012 A(H3N2) predominant influenza season, Valencia, Spain.
BACKGROUND
Most evidence of the effectiveness of influenza vaccines comes from studies conducted in primary care, but less is known about their effectiveness in preventing serious complications. Here, we examined the influenza vaccine effectiveness (IVE) against hospitalization with PCR-confirmed influenza in the predominant A(H3N2) 2011-2012 influenza season.


METHODS
A hospital-based, test-negative study was conducted in nine hospitals in Valencia, Spain. All emergency admissions with a predefined subset of symptoms were eligible. We enrolled consenting adults age 18 and over, targeted for influenza vaccination because of comorbidity, with symptoms of influenza-like-illness within seven days of admission. We estimated IVE as (1-adjusted vaccination odds ratio)*100 after accounting for major confounders, calendar time and recruitment hospital.


RESULTS
The subjects included 544 positive for influenza A(H3N2) and 1,370 negative for influenza admissions. Age was an IVE modifying factor. Regardless of vaccine administration, IVE was 72% (38 to 88%) in subjects aged under 65 and 21% (-5% to 40%) in subjects aged 65 and over. By type of vaccine, the IVE of classical intramuscular split-influenza vaccine, used in subjects 18 to 64, was 68% (12% to 88%). The IVE for intradermal and virosomal influenza vaccines, used in subjects aged 65 and over, was 39% (11% to 58%) and 16% (-39% to 49%), respectively.


CONCLUSIONS
The split-influenza vaccine was effective in preventing influenza-associated hospitalizations in adults aged under 65. The intradermal vaccine was moderately effective in those aged 65 and over.
Fundación para el Fomento de la Investigación Sanitaria y Biomédica de la Comunitat Valenciana (FISABIO), Valencia, Spain; Centro de Salud Pública de Castellón, Castellón, Spain.
Joan
J
Puig-Barberà
Instituto Valenciano de Microbiología, Valencia, Spain.
Juan
J
García-de-Lomas
Fundación para el Fomento de la Investigación Sanitaria y Biomédica de la Comunitat Valenciana (FISABIO), Valencia, Spain.
Javier
J
Díez-Domingo
Centro de Salud Pública de Castellón, Castellón, Spain.
Alberto
A
Arnedo-Pena
Centro de Salud Pública de Castellón, Castellón, Spain.
Montserrat
M
Ruiz-García
Hospital de la Plana, Vila-real, Spain.
Ramón
R
Limón-Ramírez
Hospital de la Plana, Vila-real, Spain.
Silvia
S
Pérez-Vilar
Hospital Aranau de Vilanova, Valencia, Spain.
José Luis
JL
Micó-Esparza
Hospital Doctor Peset, Valencia, Spain.
Miguel
M
Tortajada-Girbés
Hospital San Juan, Alicante, Spain; Cátedra de Medicina de Familia, Departamento de Medicina Clínica, Universidad Miguel Hernández, San Juan, Alicante, Spain.
Concha
C
Carratalá-Munuera
Hospital General de Castellón, Castellón, Spain.
Rosa
R
Larrea-González
Hospital General de Castellón, Castellón, Spain.
Juan Manuel
JM
Beltrán-Garrido
Hospital Universitario y Politécnico La Fe, Valencia, Spain.
Maria Del Carmen
Mdel C
Otero-Reigada
Hospital Universitario y Politécnico La Fe, Valencia, Spain.
Joan
J
Mollar-Maseres
Hospital Lluis Alcanyis, Xativa, Spain, 12 Centro de Salud San Blas, Alicante, Spain, 13 Hospital de Elda, Elda, Spain.
Patricia
P
Correcher-Medina
Centro de Salud San Blas, Alicante, Spain.
Germán
G
Schwarz-Chavarri
Cátedra de Medicina de Familia, Departamento de Medicina Clínica, Universidad Miguel Hernández, San Juan, Alicante, Spain; Hospital de Elda, Elda, Spain.
Vicente
V
Gil-Guillén
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D057186:Comparative Effectiveness Research; D005260:Female; D006760:Hospitalization; D006801:Humans; D053122:Influenza A Virus, H3N2 Subtype / Q000276:immunology*; D007252:Influenza Vaccines / Q000008:administration & dosage; D007251:Influenza, Human / Q000517:prevention & control*; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D013030:Spain; D055815:Young Adult
D007252:Influenza Vaccines