Influenza Vaccination Modifies Disease Severity Among Community-dwelling Adults Hospitalized With Influenza

Abstract

Background We investigated the effect of influenza vaccination on disease severity in adults hospitalized with laboratory-confirmed influenza during 2013–14, a season in which vaccine viruses were antigenically similar to those circulating. Methods We analyzed data from the 2013–14 influenza season and used propensity score matching to account for the probability of vaccination within age strata (18–49, 50–64, and ≥65 years). Death, intensive care unit (ICU) admission, and hospital and ICU lengths of stay (LOS) were outcome measures for severity. Multivariable logistic regression and competing risk models were used to compare disease severity between vaccinated and unvaccinated patients, adjusting for timing of antiviral treatment and time from illness onset to hospitalization. Results Influenza vaccination was associated with a reduction in the odds of in-hospital death among patients aged 18–49 years (adjusted odds ratios [aOR] = 0.21; 95% confidence interval [CI], 0.05 to 0.97), 50–64 years (aOR = 0.48; 95% CI, 0.24 to 0.97), and ≥65 years (aOR = 0.39; 95% CI, 0.17 to 0.66). Vaccination also reduced ICU admission among patients aged 18–49 years (aOR = 0.63; 95% CI, 0.42 to 0.93) and ≥65 years (aOR = 0.63; 95% CI, 0.48 to 0.81), and shortened ICU LOS among those 50–64 years (adjusted relative hazards [aRH] = 1.36; 95% CI, 1.06 to 1.74) and ≥65 years (aRH = 1.34; 95% CI, 1.06 to 1.73), and hospital LOS among 50–64 years (aRH = 1.13; 95% CI, 1.02 to 1.26) and ≥65 years (aRH = 1.24; 95% CI, 1.13 to 1.37). Conclusions Influenza vaccination during 2013–14 influenza season attenuated adverse outcome among adults that were hospitalized with laboratory-confirmed influenza.

Repeated influenza vaccination for preventing severe and fatal influenza infection in older adults: a multicentre case–control study

“…8 In both cases, the effect would appear as a lower frequency of severe outcomes in vaccinated patients with influenza who were admitted to hospital than in those who were unvaccinated and would have been detected in our study.…”

“…This definition has relevant implications, is easy to apply and to compare, and has been used previously. 5,8,11,12 We compared baseline characteristics between patients with influenza and controls, patients with nonsevere and severe illness, and vaccinated and unvaccinated patients with influenza. We used the χ 2 and Fisher exact tests for categorical variables and the t test for continuous variables.…”

“…5 A study in the United States reported that patients who required admis- sion to the ICU had lower influenza vaccine coverage, 9 and another found that influenza vaccination was associated with a reduction in the odds of in-hospital death and admission to the ICU among community-dwelling adults who were admitted to hospital with confirmed influenza. 8 Recent studies in Spain 11 and France 12 that involved adults admitted to hospital for influenza reported that seasonal vaccination reduced the risk of severe outcomes. Our results and the results from these other studies suggest that influenza vaccination reduces severity of disease among older patients in whom vaccination did not prevent illness caused by influenza.…”

“…7 When influenza vaccination fails to prevent illness caused by influenza, studies have suggested that vaccination may still have an additional effect by reducing the severity of disease. 5,[8][9][10][11][12][13] This vaccine effect would be of great interest among older adults, in whom the effectiveness of influenza vaccination is normally suboptimal and severe influenza is more frequent. 1,6,7 Influenza vaccination in previous seasons may retain some preventive effectiveness, [14][15][16][17] and new doses may boost the preexisting immune memory against antigenically related strains.…”

Partnering for enhanced digital surveillance of influenza‐like disease and the effect of antivirals and vaccines (PEDSIDEA)

“…The significance of the Risk‐adjusted ViVI Score indicates that physicians may be more likely to resort to antibiotics or antivirals if they perceive a patient as “too ill” in relation to the number of risk factors. Standardized risk factor data and severity data have important implications for influenza surveillance and the critical evaluation of antibiotic and antiviral use, as well as vaccine effectiveness . Surveillance programmes are strengthened enabling public health authorities to detect highly pathogenic viruses early on, even if they are prevalent at low rates .…”