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.
Competing Interests: Declaration of Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: HP reports grant funding from Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001. MKA reports grant funding from the GSK group of companies, Pfizer and Sanofi Pasteur and honoraria from Sanofi, Seqirus and Pfizer for past ad hoc advisory activities. TFH reports grants from Pfizer and GSK, outside the submitted work. AMcG reports payments to her institution from the GSK group of companies for the conduct of this study, and payments from GSK, Seqirus and Sanofi Pasteur, outside the submitted work. ML reports payments from Sanofi, Medicago, Sequirus, and Pfizer outside the submitted work. AP reports payments from Actelion, Sanofi-Pasteur, and Genentech outside the submitted work. JP reports payments from the GSK group of companies, Merck, Roche, and Synthetic Biologics, outside the submitted work. MS reports payments from the GSK group of companies and Pfizer during the study. SAM reports grants and payments from Pfizer, GSK, Merck, Novartis and Sanofi, outside the submitted work. outside the submitted work. ZS, MKN, JJL, ME, GB, WB, PL-W, LV, GT, LY, AA, JJ, KK, DR, DW, DS, GS, ST, SS, AMcC and KK report no conflicts of interest.
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