Vaccinate or Not Vaccinate? Comparative Patient Reported Outcomes on the Severity of Influenza-like-Symptoms in an Australian Community Screening Program

OBJECTIVES: Using patient-reported-outcome (PRO) measures, assess peak influenza-like-illness (ILI) symptoms among adults with acute disease across those previously vaccinated or unvaccinated for influenza.

METHODS: This study collected self-reported symptoms using the Respiratory Infection, Intensity and Impact Questionnaire (RiiQ™), from Australian adults with ILI during the 2023 influenza season. Respondents were recruited through an existing community screening program study and remunerated for participating. RiiQ™ includes 6 respiratory and 7 systemic items rated none, mild, moderate, or severe. PROs were reported by patients daily for 14 days, starting at enrollment. Influenza vaccination status was self-reported. For vaccinated vs unvaccinated arms, the relative-risk (RR) of patients reporting the highest two possible response-scores (i.e. moderate and severe) of RiiQ™ items during the most acute 5-days peak of symptoms was evaluated. We also performed a subgroup RR analysis of severe cases.

RESULTS: 105 ILI respondents, mean age 45 years, were enrolled. 47% self-reported being vaccinated. 27.3% (range 15.1-39.6) of vaccinated respondents experienced moderate or severe respiratory symptoms scales during the 5-day peak, compared to 33.5% (18.3-51.1) for unvaccinated (RR=0.81 [95%CI 0.36-1.8]). For the systemic symptoms scales, 24.8% (11.3-40.9) vs 29.9% (20.0-45.6) reported moderate or severe scores for those vaccinated vs unvaccinated, respectively (RR =0.86 [0.36-2.04]). RR of all 6 respiratory items, and 6/7 systemic ones, favored the vaccinated arm. Analyses of severe cases revealed directionally similar findings for all items, with lower RR of symptoms for vaccinated patients in the 5-day peak (RR=0.52 [0.1-2.83] for respiratory and RR=0.46 [0.07-3.1] for systemic).

CONCLUSIONS: Influenza vaccination may result in milder ILI symptoms during the early, peak-stages of infection. Complementing classical trial endpoints, disease-specific PROs such as the RiiQ™ can provide unique insights into milder symptom severity, denoting an additional benefit of vaccination. Larger cohorts with lab-confirmation of influenza are needed to overcome the limitations of this study.