Vaccine Effectiveness of non-adjuvanted and adjuvanted trivalent inactivated influenza vaccines in the prevention of influenza-related hospitalization in older adults: A pooled analysis from the Serious Outcomes Surveillance (SOS) Network of the Canadian Immunization Research Network (CIRN).

BACKGROUND: Influenza vaccines prevent influenza-related morbidity and mortality; however, suboptimal vaccine effectiveness (VE) of non-adjuvanted trivalent inactivated influenza vaccine (naTIV) or quadrivalent formulations in older adults prompted the use of enhanced products such as adjuvanted TIV (aTIV). Here, the VE of aTIV is compared to naTIV for preventing influenza-associated hospitalization among older adults. METHODS: A test-negative design study was used with pooled data from the 2012 to 2015 influenza seasons. An inverse probability of treatment (IPT)-weighted logistic regression estimated the Odds Ratio (OR) for laboratory-confirmed influenza-associated hospitalization. VE was calculated as (1-OR)*100% with accompanying 95% confidence intervals (CI). RESULTS: Of 7,101 adults aged ≥ 65, 3,364 received naTIV and 526 received aTIV. The overall VE against influenza hospitalization was 45.9% (95% CI: 40.2%-51.1%) for naTIV and 53.5% (42.8%-62.3%) for aTIV. No statistically significant differences in VE were found between aTIV and naTIV by age group or influenza season, though a trend favoring aTIV over naTIV was noted. Frailty may have impacted VE in aTIV recipients compared to those receiving naTIV, according to an exploratory analysis; VE adjusted by frailty was 59.1% (49.6%-66.8%) for aTIV and 44.8% (39.1%-50.0%) for naTIV. The overall relative VE of aTIV to naTIV against laboratory-confirmed influenza hospital admission was 25% (OR 0.75; 0.61-0.92), demonstrating statistically significant benefit favoring aTIV. CONCLUSIONS: Adjusting for frailty, aTIV showed statistically significantly better protection than naTIV against influenza-associated hospitalizations in older adults. In future studies, it is important to consider frailty as a significant confounder of VE.

Influenza vaccination and major adverse vascular events in high-risk patients

Background—We sought to determine the association between influenza vaccination and major adverse vascular events because the association remains uncertain.Methods and Results—A total of 31 546 participants were enrolled from 40 countries. Eligibility included age 55 years and known vascular disease. The primary outcome was a composite of death resulting from cardiovascular causes, myocardial infarction, or stroke during 4 influenza seasons (2003–2007). Influenza vaccination was associated with a lower risk of the outcome during 3 influenza seasons (defined using World Health Organization FluNet reports): 2004to 2005 (adjusted odds ratio [OR], 0.62; 95% confidence interval [CI], 0.50–0.77), 2005 to 2006 (adjusted OR, 0.69; 95% CI, 0.53– 0.91), and 2006 to 2007 (adjusted OR, 0.52; 95% CI, 0.42– 0.65), the same years that circulating influenza matched the vaccine antigen. In 2003 to 2004, there was an incomplete match between circulating influenza and the vaccine antigen, and there was no association between influenza vaccination and the outcome (adjusted OR, 0.96; 95% CI, 0.73–1.27). However, tests of potential biases in the analyses revealed associations between influenza vaccination and outcome during noninfluenza seasons except 2003 to 2004. The summary ORs in the influenza season (OR, 0.65; 95% CI, 0.58–0.74]) and noninfluenza season (OR, 0.66; 95% CI, 0.57– 0.76) were almost identical. The reduction in risk of noncardiovascular death associated with the influenza vaccine ranged from 73% to 79%.Conclusion—Although initial analyses suggest that influenza vaccination was associated with reduced risk of majoradverse vascular events during influenza seasons when the influenza vaccine matched the circulating virus, sensitivity analyses revealed that risk of bias remained. A randomized trial is needed to definitively address this question.