Is there a best time to get the vaccine to reduce waning?

The short version: timing matters, but the benefit is small and the evidence is messy. Getting the shot in late October or early November, about 2-4 weeks before flu season peaks, probably gives you the best chance of protection when you need it most.

The evidence for waning is real but inconsistent. A large US study across four seasons found that protection against H3N2 dropped from 35% at 14 days after the shot to zero at 158 days [1]. Against H1N1 it fell from 80% to 37% over 128 days [1]. A UK study from 2011-12 showed the same pattern: 53% protection if vaccinated less than three months before exposure, falling to 12% if three months or more had passed [4]. But a 2017-18 pediatric study found no waning at all [3], and an Australian study from 2012 also found no significant decline [2]. The difference may come down to which strain is circulating, how well the vaccine matches it, and how the study handles a statistical trap called "depletion of susceptibles" [5].

For a fit 69-year-old man, the practical question is when flu season peaks in your region. In most of the US and Europe, that is January through March. Getting vaccinated in late October or early November puts peak antibody levels right in that window. Vaccinating in August or September risks having protection fade by February [1, 4]. Vaccinating in December or January leaves you unprotected during the early part of the season.

The confidence intervals are wide and many estimates are not statistically significant. The evidence supports delaying vaccination until close to the season start, but the benefit of that timing is modest and depends on the year's match.

My call: for a fit 69-year-old man, aim for late October or early November, about 2-4 weeks before local flu season typically peaks. This gives the best chance of protection when flu is circulating. Confidence: moderate.