Flu Vaccine Tied to Lower Symptom Scores in Children, Faster Relief in Adults

Influenza vaccination was associated with lower daily influenza-like illness (ILI) and lower respiratory tract involvement (LRTI) symptom scores among ambulatory children with laboratory-confirmed influenza, according to a multicenter analysis published online in Clinical Infectious Diseases. Among adults, vaccination was not associated with reduced symptom burden but was associated with faster alleviation of ILI symptoms.

Investigators analyzed case-ascertained household transmission studies conducted at multiple US sites during the 2017-2018 through 2022-2023 seasons, excluding 2020-2021 because influenza activity was minimal. Participants completed daily symptom diaries and provided respiratory specimens. The analysis included 869 children, of whom 354 were vaccinated, and 653 adults, of whom 277 were vaccinated.

In adjusted mixed-effects models, vaccinated children had lower mean daily ILI scores than unvaccinated children (mean difference, -0.16; 95% CI, -0.32 to -0.01) and lower LRTI scores (mean difference, -0.18; 95% CI, -0.34 to -0.01). The unweighted all-symptom score did not differ significantly. No adjusted symptom-score differences were observed between vaccinated and unvaccinated adults.

Vaccination was not associated with time to symptom alleviation in children across any of the three scores. In adults, however, vaccinated participants had a higher adjusted rate of ILI symptom alleviation than unvaccinated participants (adjusted hazard ratio, 1.30; 95% CI, 1.04-1.62). The adjusted results for LRTI and unweighted symptom alleviation did not show statistically significant differences.

The authors noted that the ambulatory cohort may not represent the mildest or most severe influenza cases, influenza type and subtype were not examined, participation was voluntary, time-to-alleviation analyses used full-day intervals, and findings may not generalize to other regions. They concluded that vaccination was associated with lower ILI burden but not shorter symptom duration in children, and with faster ILI symptom alleviation but not lower symptom burden in adults.

Source: Howa AC, Zhu Y, McGonigle T, et al. Influenza vaccination and symptom burden in ambulatory patients with confirmed influenza: evidence from case-ascertained household transmission studies. Clin Infect Dis. Published online August 13, 2026. doi:10.1093/cid/ciag486