- During the 2017-2018 influenza season, overall vaccine effectiveness (VE) against influenza A(H3N2) and B among older EU adults was only 24%.
- Despite trivalent vaccine and circulating B mismatch, seasonal influenza VE (IVE) was still greater against influenza B vs A(H3N2), suggesting cross-protection.
Why this matters
Clinicians should encourage influenza vaccine uptake among older patients, even in seasons using trivalent vaccine with circulating influenza B lineage mismatch and adapted egg-propagated vaccine virus.
- 3483 patients (1455 positive for any influenza type; 2028 negative):
- 376 influenza A(H3N2), 299 influenza B/Yamagata, 26 B/Victoria.
- Influenza A(H3N2):
- Pooled adjusted IVE: 24% (95% CI, 2%-40%).
- IVE by age:
- 35% (6%-55%) for age 65-79 years, vs
- 14% (−22% to 39%) for age ≥80 years.
- Influenza B:
- Pooled adjusted IVE: 30% (95% CI, 16%-41%).
- IVE by age:
- 37% (19%-51%) for 65-79 years, vs
- 19% (−7% to 38%) for ≥80 years.
- ~2 of 3 of patients with influenza had underlying cardiovascular disease.
- Prospective, test-negative design, pooled analysis of 2017-2018 seasonal IVE against hospitalization with influenza A(H3N2), influenza B among older, hospitalized adults age ≥65 years, by age group, comorbidities, and prior season vaccination across 9 EU countries, 2017-2018.
- Funding: Horizon 2020.
- Small sample size.
- Possible misclassification bias.