Take away:

If correct numerators and denominators are used, COVID-19 is at least 10 times as deadly as seasonal influenza.

The claim:

The Infection Fatality Ratio for COVID-19 is “approximately 2.5 times higher than the estimated IFR for seasonal influenza.”

The evidence:

Blackburn et al. report an infection fatality ratio among community-living adults of 0.26% (1). If institutionalized adults had been included the ratio would be higher, likely approximating the 0.6% mortality rate among exposed individuals readily calculated by combining official death tolls, the known 30% undercount (2), and a definitive CDC study that found 10 times as many people have been exposed to the novel coronavirus than are reported as cases (3). Among the elderly, Blackburn et al. calculate COVID-19 is 2.5 times deadlier than seasonal flu. This is clearly an underestimate:

1) Blackburn et al. use CDC estimates of case-fatality rates calculated on the basis of all Americans, including the institutionalized, not limited to much healthier community-dwellers.

2) The seasonal influenza case fatality rates reported by the CDC, including the often cited 0.1% overall, are for symptomatic cases. Their denominators are estimated by using the reported number of influenza hospitalizations to guess the burden of clinical illness (4). But antibody studies show that 65%-85% of people infected with influenza never develop symptoms (5). The 0.6% mortality rate calculated here for SARS-CoV-2-exposed individuals is 6 times higher than the 0.1% usually cited for seasonal influenza. Given the overestimation of commonly accepted influenza mortality rates due to failure to take asymptomatic infections into account, SARS-CoV-2 can be seen to be not 2.5 times, or even 6 times, but at least 10 times as lethal as seasonal flu.

Sources:

1 http://www.acpjournals.org/doi/10.7326/M20-5352

2 https://jamanetwork.com/journals/jamainternalmedicine/fullarticle/2767980

3 https://jamanetwork.com/journals/jamainternalmedicine/fullarticle/2768834

4 https://www.cdc.gov/flu/about/burden/how-cdc-estimates.htm

5 https://pubmed.ncbi.nlm.nih.gov/26133025/