In new guidance for mathematical modelers and public health officials, the US Centers for Disease Control and Prevention is estimating that about a third of coronavirus infections are asymptomatic.

The CDC also says its "best estimate" is that 0.4% of people who show symptoms and have Covid-19 will die, and the agency estimates that 40% of coronavirus transmission is occurring before people feel sick.

The agency cautions that those numbers are subject to change as more is learned about Covid-19, and it warns that the information is intended for planning purposes. Still, the agency says its estimates are based on real data collected by the agency before April 29.

The numbers are part of five planning scenarios that "are being used by mathematical modelers throughout the federal government," according to the CDC. Four of those scenarios represent "the lower and upper bounds of disease severity and viral transmissibility."

The fifth scenario is the CDC's "current best estimate about viral transmission and disease severity in the United States." In that scenario, the agency described its estimate that 0.4% of people who feel sick with Covid-19 will die.

For people age 65 and older, the CDC puts that number at 1.3%. For people 49 and under, the agency estimated that 0.05% of symptomatic people will die.

Expert pushes back

Under the most severe of the five scenarios outlined -- not the agency's "best estimate" -- the CDC lists a symptomatic case fatality ratio of 0.01, meaning that 1% of people overall with Covid-19 and symptoms would die.

In the least severe scenario, the CDC puts that number at 0.2%.

One expert quickly pushed back on the CDC's estimates.

"While most of these numbers are reasonable, the mortality rates shade far too low," biologist Carl Bergstrom of the University of Washington told CNN.

Bergstrom, an expert in modeling and computer simulations, said the numbers seemed inconsistent with real-world findings.

"Estimates of the numbers infected in places like NYC are way out of line with these estimates. Let us remember that the number of deaths in NYC right now are far more than we would expect if every adult and child in the city had been infected with a flu-like virus. This is not the flu. It is COVID," Bergstrom said.

"As I see it, the 'best estimate' is extremely optimistic, and the 'worst case' scenario is fairly optimistic even as a best estimate. One certainly wants to consider worse scenarios," Bergstrom said of CDC's numbers.

"By introducing these as the official parameter sets for modeling efforts, CDC is influencing the models produced by federal agencies, but also the broader scientific discourse because there will be some pressure to use the CDC standard parameter sets in modeling papers going forward," he said.

"Given that these parameter sets underestimate fatality by a substantial margin compared to current scientific consensus, this is deeply problematic."

Numbers are for planning purposes, CDC says

"The scenarios are intended to advance public health preparedness and planning. They are not predictions or estimates of the expected impact of COVID-19," the CDC says.

It says the numbers do not "reflect the impact of any behavioral changes, social distancing, or other interventions," which would be relevant for some of the agency's estimates -- such as how many infections stem from each case

Still, the CDC is characterizing the numbers as preliminary estimates from federal agencies, including the CDC and the HHS Office of the Assistant Secretary for Preparedness and Response, that are "designed to help inform decisions by modelers and public health officials who utilize mathematical modeling."

Under the best estimate scenario, the guidance says 3.4% of symptomatic people with Covid-19 will require hospitalization, with that number rising to 7.4% in people 65 and older. The CDC also says it assumes that people without symptoms are just as infectious as those with symptoms.

The CDC estimated .40 death rate is close to the German study that came up with .37 death rate for COVID19 in their study. I think the picture is getting clearer on what is actually going on.

I think this criticism of the estimates is very damning (ie applying the model to a real life situation and finding it does not work at all) :-

Estimates of the numbers infected in places like NYC are way out of line with these estimates. Let us remember that the number of deaths in NYC right now are far more than we would expect if every adult and child in the city had been infected with a flu-like virus. This is not the flu. It is COVID," Bergstrom said.

But it is still early days and we need good antibody testing to get closer to the truth.     One thing that I have noticed is that this virus seems to work well is clusters.   This will mean that if you are in a cluster area then the figures for that area will be much worse than average, and elsewhere could be much better than average.  We might need a model with at least two estimates - one for cluster situations, and one were there is only minimal spread.  

The bigger the cohort, the more accurate the statistics.

BBC News24 just before 12pm today: 5 million infected worldwide, 1/3 million dead.  

AI, the maths was OK, but it is clear that many countries are under reporting deaths (eg Qatar with a CFR of 0.04%, where as neighbour UAE is at 0.9%, or Russia at 0.98%), and other countries seem to have stopped reporting (such as Tanzania).  The data we are being given is quite bad. 

I do hope some of the figures that you are quoting are good, but I have little confidence in what we are being told. 

Nearer home the first results from the anti-body tests in Helsinki, Finland were a great disappointment as far fewer people had anti-bodies than the models expected. So in that case the IFR must have been much higher than had been used in the main models.  Other results point to a smaller IFR, but it seems the results are all over the place.

This is a good video explaining a study done in Indiana. They put the asymptomatic rate at 45%. 

https://youtu.be/4XWbBTwAsUM - https://youtu.be/4XWbBTwAsUM

I believe approx. 35% of all flu cases are also asympto.