Seasonal Influenza A H1N1pdm09 Virus and Severe Outcomes: A Reason for Broader Vaccination in Non-Elderly, At-Risk People.
BACKGROUND
Recent pandemics of influenza A H1N1pdm09 virus have caused severe illness, especially in young people. Very few studies on influenza A H1N1pdm09 in post-pandemic periods exist, and there is no information on the severity of both seasonal influenza A(H1N1) and A(H3N2) from the same season, adjusting for potential confounders, including vaccine.


RESULTS
We performed a retrospective observational study of adults hospitalized during the 2014 season with influenza A(H1N1) or A(H3N2). All patients underwent the same diagnostic and therapeutic protocol in a single hospital, including early Oseltamivir therapy. We included 234 patients: 146 (62.4%) influenza A(H1N1) and 88 (37.6%) A(H3N2). A(H1N1) patients were younger (p<0.01), developed more pneumonia (p<0.01), respiratory complications (p = 0.015), ARDS (p = 0.047), and septic shock (p = 0.049), were more frequently admitted to the ICU (p = 0.022), required IMV (p = 0.049), and were less frequently vaccinated (p = 0.008). After adjusting for age, comorbidities, time from onset of illness, and vaccine status, influenza A(H1N1) (OR, 2.525), coinfection (OR, 2.821), and no vaccination (OR, 3.086) were independent risk factors for severe disease.


CONCLUSIONS
Hospitalized patients with influenza A(H1N1) were more than twice as likely to have severe influenza. They were younger and most had not received the vaccine. Our findings suggest that seasonal influenza A(H1N1) maintains some features of pandemic viruses, and recommend wider use of vaccination in younger adult high-risk patients.
Servicio de Neumología, Hospital Universitario Miguel Servet, Zaragoza, Spain.
Elisa
E
Minchole
Servicio de Neumología, Hospital Universitario Miguel Servet, Zaragoza, Spain.
Ana L
AL
Figueredo
Servicio de Microbiología, Hospital Universitario Miguel Servet, Zaragoza, Spain.
Manuel
M
Omeñaca
Servicio de Neumología, Hospital Universitario Miguel Servet, Zaragoza, Spain.
Carolina
C
Panadero
Servicio de Neumología, Hospital Universitario Miguel Servet, Zaragoza, Spain.
Laura
L
Royo
Servicio de Neumología, Hospital Universitario Miguel Servet, Zaragoza, Spain.
Jose J
JJ
Vengoechea
Servicio de Neumología, Hospital Universitario Miguel Servet, Zaragoza, Spain.
Sergio
S
Fandos
Servicio de Neumología, Hospital Universitario Miguel Servet, Zaragoza, Spain.
Francisco
F
de Pablo
Servicio de Neumología, Hospital Universitario Miguel Servet, Zaragoza, Spain.
Salvador
S
Bello
D000208:Acute Disease; D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D000998:Antiviral Agents / Q000627:therapeutic use; D006760:Hospitalization; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000187:drug effects / Q000302:isolation & purification*; D053122:Influenza A Virus, H3N2 Subtype / Q000187:drug effects / Q000302:isolation & purification; D007252:Influenza Vaccines / Q000627:therapeutic use*; D007251:Influenza, Human / Q000150:complications* / Q000175:diagnosis / Q000188:drug therapy / Q000517:prevention & control*; D008875:Middle Aged; D053139:Oseltamivir / Q000627:therapeutic use; D011014:Pneumonia / Q000209:etiology / Q000821:virology; D012128:Respiratory Distress Syndrome / Q000209:etiology / Q000821:virology; D012189:Retrospective Studies; D012307:Risk Factors; D012621:Seasons; D012772:Shock, Septic / Q000209:etiology / Q000821:virology; D016896:Treatment Outcome; D055815:Young Adult
D000998:Antiviral Agents; D007252:Influenza Vaccines; D053139:Oseltamivir