That is an unlikely hypothesis, given that we didn't see an exponential explosion in deaths, and people going to the hospital until February.
Either:
1. The virus was for some reason less lethal before February.
2. Only people who don't show symptoms were catching it.
3. The serological studies are mostly finding false positives.
My money's on #3.
This happened with someone that survived SARS-CoV having effective antibodies against CoV-2: https://www.nature.com/articles/s41586-020-2349-y
If that happened, the population would be very largely skewed towards the most vulnerable (you usually don't go to ER or a hospital if you're healthy) and that would explain the uptick in deaths.
There's no other idea I can offer to explain why a disease with an estimated IFR between 0.5 and 0.9% would cause an order of magnitude more deaths.
I have been idly tracking the data here in WA. 90% of the deaths have been in 60+ years of age. Just ~30% percent of the cases. In that age range, the CFR is staggeringly high. I don't know the data for the numbers from nursing homes.
From looking at the numbers, I can't help but think we really failed protecting the elder population.
The unmitigated doubling time of COVID-19 seems to be around 2.5 days. So if about 1% gets hospitalized and people noticed after 10 or so patients with the same symptoms (that's before any of them died, mind you) you'd need about 1000 people infected. To go from 1 infected person to 1000 takes log2(1000)=9.96 doublings. So if the doubling time is 2.5 that would be 25 days or over 3 weeks before anyone would notice.
Some of these numbers are a bit of a guess but I'm trying to show that "exponential explosion" can be very small and slow at the very beginning of an outbreak.
On average an infected person seems to spread it to 2-3 persons, but we don't know the variance. It could be something like 8/10 spread it to zero persons, 1 to 4 persons and 1 to 16 persons. With low number of infected that would make the increase very noisy. In fact, it has to be so, otherwise Covid19 would explode everywhere and not be more or less containable. It has to catch momentum or whatever.
As in unlucky happenstance means three infected people in a tour group show up and infect two to three dozen people each over a weekend. You go from 3 to 100 cases in two days. R instead of being 2.5 jumped to 30!
After a week just with normal spreading you have close to a 1000 people ill.
#1 and #2 sound not entirely implausible to me though... Severity of disease seems to vary a lot with infection dose. Is it really that far fetched that when infection doses are very low the disease is mild, but as the virus level in the population rises and infection doses go up the disease becomes a very serious public health issue?
Does anybody know any data that supports/refutes my thinking above?
Remember, for #2, it is not that most people stay asymptomatic. They are usually pre-symptomatic, and do have the symptoms later. Just for the majority of folks <60, they are a bad cold. If you are under 20, not even a bad one.
And from some comments down thread, #3 is as likely to be wrong with these having more false negatives. So, tough to say.
"The test had a 98.3% specificity and 100% sensitivity"
I.e. only 1.7% likelihood of false positives
EDIT: And no case was missed
Seems rather more complex than the common account.
For the age group < 10 yo, the estimated IFR is 0.002%
For the age group 10 - 19 yo, the estimated IFR is 0.003%
For the age group 20 - 49 yo, the estimated IFR is 0.002%
For the age group 50 - 69 yo, the estimated IFR is 0.04%
For the age group > 70 yo, the estimated IFR is 4.1%
The study is considered to be well designed by Carl Bergstrom[2], for example.
[1]: https://www.mscbs.gob.es/profesionales/saludPublica/ccayes/a... Look for the table on page 15.
[2]: https://twitter.com/CT_Bergstrom/status/1261041466882678784
Were you trolling, ignorant of current news, or what exactly?
According to Spanish government's estimates[1] based on their own seroprevalence study:
For the age group under 50, the estimated IFR is about 0.003%
For the age group 50 - 69 yo, it's 0.04%
And for those over 70, it's 4.1%
The study is considered to be well designed by Carl Bergstrom[2], for example.
[1]: https://www.mscbs.gob.es/profesionales/saludPublica/ccayes/a... Look for the table on page 15.
[2]: https://twitter.com/CT_Bergstrom/status/1261041466882678784