flu death rate vs covid-19 death rate

[oatgla]

If the estimated count of those infected from flu last flu season was 1 billion and the estimated flu death count(the highest i've read) is 650,000, how are they coming up with a flu death rate of .1% shouldn't it be less than that? and if it is does that mean the covid-19 death rate is being calculated wrong as well? 

Dr Fauci on the news said the flu death rate is .1% and covid-19 is .4%

 

"Influenza is a highly contagious respiratory illness that is responsible for significant morbidity and mortality. Approximately 9% of the world’s population is affected annually, with up to 1 billion infections, 3 to 5 million severe cases, and 300,000 to 500,000 deaths each year.^1–3' "

 

So if 1 billion are being infected, this quote says 500,000, but ive seen up to 650,000 deaths, how are they coming up with a death rate of .1% shouldn't it be less?

Sorry if I posted in wrong section, first post :)

[Strange]

!

Moderator Note

Moved to Medical Science (seems slightly more appropriate)

 

[CharonY]

There are different measures of death rates that are often used interchangeably in the press. However, the calculations are different (and it does not help that the lingo is often mixed in different disciplines). But first with regard to the last flu season, the numbers are not fully in it and the 0.1% are "typical" values. However, estimates are not even fully done for the season before last and this season there are still only estimates, which will be heavily confounded by the COVID-19 pandemic (e.g. due to stress on the health system in many countries). The 0.1% you have seen are based on overall estimates, not specific seasons, there are some which are worse, others which are better.

Going back to the estimates. What is often mixed up are the following terms: Infection fatality rate. This is what you probably think about and which is ratio of death based on total infected folks. The problem is that these values are only ever estimated as infections are missed or not systematically tracked. The other more commonly used one is the case-fatality rate which is based on diagnosed cases only. The latter will have a higher fatality rate than the former. Making it more complicated, flu is often not verified by laboratory testing but based on symptoms. This skews that data further and we get what is often called the symptomatic case-fatality rate. I.e. the proportion of symptomatic patients that eventually die. I.e. non-symptomatic patients would not be counted here. Based on the estimates of asymptomatic influenza carrier the infection fatality rate is estimated to be half to down to a quarter of the case-fatality (i.e. 0.025-0.05%).

Then we also have the crude fatality count, which dominated much of the press reporting, which is just taking what actually have been measured so far. But as we know, there is a lot of undertesting which results in yet higher fatality rates (i.e. the 2% and higher you might have seen). There are different papers out there modeling the infection fatality rate for COVID-19 and I have seen values ranging from 0.3-1.6%.

Now what is only half of the story when we talk about disease burden. The other half is understanding how many folks are actually at risk getting sick. Due to immunity within the population and availability of vaccines as well as properties of the virus itself about 3-11% of the population (using US-estimates) each year are usually sickened by influenza. Due to lack of immunity the number folks that may get COVID-19 (without barriers in place) is estimated to be between 50-80% (assuming folks that get sick develop immunity and do not get sick again). So taking together based on current estimates (which by no means are final) the difference is at least sixfold if we only consider infection fatalities rather than mixing) and we have got an about 10-fold higher pool of susceptible folks. I.e. serious as the flu is, COVID-19 has clearly the potential to become worse without protective measures as countries, including the US are finding out.