Effects of previous episodes of influenza and vaccination in preventing laboratory-confirmed influenza in Navarre, Spain, 2013/14 season.
We estimated whether previous episodes of influenza and trivalent influenza vaccination prevented laboratory-confirmed influenza in Navarre, Spain, in season 2013/14. Patients with medically-attended influenza-like illness (MA-ILI) in hospitals (n = 645) and primary healthcare (n = 525) were included. We compared 589 influenza cases and 581 negative controls. MA-ILI related to a specific virus subtype in the previous five seasons was defined as a laboratory-confirmed influenza infection with the same virus subtype or MA-ILI during weeks when more than 25% of swabs were positive for this subtype. Persons with previous MA-ILI had 30% (95% confidence interval (CI): -7 to 54) lower risk of MA-ILI, and those with previous MA-ILI related to A(H1N1)pdm09 or A(H3N2) virus, had a, respectively, 63% (95% CI: 16-84) and 65% (95% CI: 13-86) lower risk of new laboratory-confirmed influenza by the same subtype. Overall adjusted vaccine effectiveness in preventing laboratory-confirmed influenza was 31% (95% CI: 5-50): 45% (95% CI: 12-65) for A(H1N1)pdm09 and 20% (95% CI: -16 to 44) for A(H3N2). While a previous influenza episode induced high protection only against the same virus subtype, influenza vaccination provided low to moderate protection against all circulating subtypes. Influenza vaccine remains the main preventive option for high-risk populations.
Instituto de Salud Pública de Navarra, IdiSNA - Navarra Institute for Health Research, Pamplona, Spain.
Jesús
J
Castilla
Ana
A
Navascués
Mirian
M
Fernández-Alonso
Gabriel
G
Reina
Esther
E
Albéniz
Francisco
F
Pozo
Nerea
N
Álvarez
Iván
I
Martínez-Baz
Marcela
M
Guevara
Manuel
M
García-Cenoz
Fátima
F
Irisarri
Itziar
I
Casado
Carmen
C
Ezpeleta
D000293:Adolescent; D000328:Adult; D000368:Aged; D016022:Case-Control Studies; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000276:immunology* / Q000302:isolation & purification; D053122:Influenza A Virus, H3N2 Subtype / Q000276:immunology* / Q000302:isolation & purification; D009981:Influenza B virus / Q000276:immunology* / Q000302:isolation & purification; D007252:Influenza Vaccines / Q000008:administration & dosage / Q000276:immunology*; D007251:Influenza, Human / Q000453:epidemiology / Q000517:prevention & control* / Q000821:virology; D008297:Male; D008875:Middle Aged; D017063:Outcome Assessment, Health Care; D016133:Polymerase Chain Reaction / Q000379:methods; D011159:Population Surveillance; D011320:Primary Health Care; D012621:Seasons; D012680:Sensitivity and Specificity; D018571:Sentinel Surveillance; D013030:Spain / Q000453:epidemiology; D014611:Vaccination / Q000706:statistics & numerical data; D064166:Vaccine Potency; D055815:Young Adult
D007252:Influenza Vaccines
Influenza; case control study; influenza vaccine; influenza-like illness; vaccine effectiveness