Peer-reviewed IFR estimates for (seasonal) influenza?
It seems every journalist has his favorite expert that they can quote to whip up a CFR or IFR number for influenza. (For example, a question here [which no longer has this information] said that the IFR for influenza is 0.1%, although I think the unclear passages in the sources cited e.g. are actually talking about CFR. A Bloomberg piece which is more clear/explicit that it is talking about IFR puts it at 0.04%, but again the source is some expert interviewed.)
It seems substantially harder to find some meta-analysis giving such IFR figures for influenza.
What I could find in the peer-reviewed literature is that the asymptomatic rate for influenza isn't a slam dunk:
Most point estimates from studies of outbreak investigations fell in the range 4%–28% with low heterogeneity (I2=0%) with a pooled mean of 16% (95% CI: 13%, 19%). Estimates from the studies conducted across epidemics without adjustment were very heterogeneous (point estimates 0%–100%; I2=97%), while estimates from studies that adjusted for background illnesses were more consistent with point estimates in the range 65%–85% and moderate heterogeneity (I2=58%). Variation in estimates could be partially explained by differences in study design and analysis, and inclusion of mild symptomatic illnesses as asymptomatic in some studies.
So it doesn't look like one can resort to a generally accepted asymptomatic ratio and simply multiply any random CFR from influenza studies with that.
Not that the CFR for influenza seems very easy to pin down either, e.g. a meta-analysis on 77 studies on the H1N1/pdm09 CFR found a large range. Oddly, this paper's abstract doesn't report the more usual meta-analytic attempts at some central value with confidence intervals.
We identified very substantial heterogeneity in published estimates, ranging from less than 1 to more than 10,000 deaths per 100,000 cases or infections. The choice of case definition in the denominator accounted for substantial heterogeneity, with the higher estimates based on laboratory-confirmed cases (point estimates = 0-13,500 per 100,000 cases) compared with symptomatic cases (point estimates = 0-1,200 per 100,000 cases) or infections (point estimates = 1-10 per 100,000 infections). Risk based on symptomatic cases increased substantially with age.
So yes, they estimated the IFR for H1N1/09 to just 0.001% to 0.01%. But supposedly the seasonal influenza, H3N2 in particular, is more deadly than H1N1 (but even that relative proportion might vary with the age group.)
But perhaps there is less disagreement on the CFR for seasonal influenza.
So, are there such IFR (not CFR) estimates for seasonal influenza? In particular, I'm most interested in global estimates rather than focused on one country and in meta-analytical results rather than single (outbreak/season) studies, but I'll relax my requirements if they are too strict in producing any answer.
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