Influenza vaccine effectiveness in older adults: study methods, transparency and impacts on public health

We re-read the article by Domnich et al. [1] following citation in a recently-published ECDC report [2]. Domnich et al. conducted a post-hoc, test-negative case-control design (TND) study of Italian hospitalizations (using DRIVE [3] data) and estimated relative effectiveness (rVE) of 59.2% for adjuvanted vs unadjuvanted influenza vaccination, which was influential in ECDC conclusions. These results directionally contradict Italian hospitalized results from DRIVE itself which reported lower adjusted VE for adjuvanted than non-adjuvanted vaccine in both 2018/19 (34% [−12–61] for adjuvanted vs 92% [40–99] for Fluarix Tetra) [4] and 2019/2020 (52% [27–68] vs 67% [8–88]) seasons, findings associated with negative, rather than positive, adjuvanted rVE [5].