A simulation-based probabilistic decision analysis using U.S. outpatient influenza surveillance data from 14 seasons (2010–2019 and 2023–2026) identified MMWR weeks 47–48—late November through early December—as the optimal window for single-dose influenza vaccination. Compared with week 44, near the tail end of current CDC guidance's September–October window, vaccinating in week 47–48 reduced modeled influenza-weighted outpatient burden by 50 visit equivalents per 10,000 weekly encounters, a meaningful if not dramatic margin.
This finding directly challenges longstanding public health messaging that nudges Americans to vaccinate before November. The core tension—vaccine waning versus epidemic timing uncertainty—has long been acknowledged anecdotally, but quantifying the optimal week with uncertainty modeling across epidemic variability adds genuine methodological value. Prior observational work has hinted that early-season vaccination correlates with reduced mid-season effectiveness, particularly in older adults, and this model formalizes that tradeoff.
Critical limitations temper enthusiasm: the model optimizes for outpatient burden rather than hospitalizations or mortality, excludes population-level transmission dynamics, and assumes vaccination actually occurs at the target week—an optimistic behavioral assumption. The analysis also cannot capture year-specific viral strain mismatches that dominate real-world effectiveness. Crucially, this is a preprint posted on medRxiv and has not yet undergone peer review; findings and model assumptions may shift substantially. Still, this represents a potentially practice-relevant, incrementally paradigm-shifting contribution to vaccination timing policy worth tracking through peer review.