My readings show that experts feel we are out of the Covid epidemic as a country when the daily case rate over the United States is somewhere around 5,000 and when the daily positivity rate is around 1.0%. California hits those levels at around May 18th. The US as a whole hits a “Fauci” level end-June. We have much to look forward to if we continue doing together what has worked to prevent Covid
Back in March and April a year ago, I tried to do forecasting models and project the end of Covid numerically, but couldn’t. Not just because I’m inherently pessimistic in health (I am), but in all my simulations (SEIR was the best), there was always some Covid epidemic staying with us. It didn’t bother me, I assumed that looking out to 2021 / 2022 was probably nonsense anyway but now we’re in 2021, and looking at 2022 for vaccinations for elementary school children, so I asked myself again:
We hear the word epidemic, and hear many things — many shades of gray. The CDC writes:
“Epidemic refers to an increase, often sudden, in the number of cases of a disease above what is normally expected in that population in that area.”
Specifics of “population in that area”, and “number of cases” and “normally expected” of course are shades of grey.
Covid of course is remarkable since we “expected” zero cases: it’s a new disease. Any level of Covid would be an epidemic by definition, so would we expect that the epidemic is over when there is zero covid? Yes, but there’s a catch.
From many health sources:
We will never be at zero Covid cases in the future. Covid is here to stay.
That having been said then the question goes back: what is then the ‘new normal’ for Covid, such that we would consider the epidemic over in the country, knowing we will never get to “Zero Covid”.
Anthony Fauci (I don’t need introduction) has been clear in 2020, and in 2021:
“(CNN 5/March) — The US shouldn’t ease restrictions in place to prevent Covid-19 before the number of new coronavirus cases falls below 10,000 daily, “and maybe even considerably less than that,” Dr. Anthony Fauci said Thursday.”
Note, that we’re not hearing of vaccinations (“herd immunity at 70%, no 80%, no 85%), deaths, or other factors, but specifically cases.
Dr. Fauci is more optimistic than other doctors in the field.
Take “Paul Offit, the director of the Vaccine Education Center and an expert in virology and immunology at the Children’s Hospital of Philadelphia.”
In a February article in The Atlantic, (https://www.theatlantic.com/health/archive/2021/02/how-know-when-pandemic-over/618122/) we read:
In his view, “the doors will open” when the country gets to fewer than 5,000 new cases a day, and fewer than 100 deaths.
This is approximately the same as a normal flu season, so we are seeing a definition of covid consistent with an epidemic that would, with the CDC Defnition read like:
(Paraphrased) “Epidemic COVID refers to an increase, often sudden, in the number of cases of a disease above what is normally expected from a comparable virally transmitted infection like the Flu, in that population in that area.”
In the same Atlantic article, we read from Joseph Eisenberg, an epidemiologist at the University of Michigan about the Flu comparison:
“This risk [Flu infection and fatality] was largely considered acceptable by the public,”
One thing I noticed in my COVID epidemic simulations was what I called the “freak out factor” when daily fatalities exceeded a certain level, people dramatically increased masking and isolation… and fatalities dropped until they were at an acceptable level, then suddenly certain states would declare success and re-open. That’s the “acceptable risk” view.
I’m hearing therefore somewhere in the range of 5,000 to 10,000 new cases per day as the exit threshold by comparisons with Flu, and acceptable infection and death rates.
Still I find this a difficult definition of epidemic exit or “threshold”, because measurement of Flu and Covid are different, and we don’t do flu testing anywhere at the level we do for Covid. Are there other endpoints?
Not really. CDC, from my searching, communicates nothing about “exiting the epidemic” or similar, which is unfortunate. It’s all an unrelenting drumbeat of doom. But more about that later.
In California ( https://covid19.ca.gov/safer-economy/ ) , the definition of “Minimal” threshold for the epidemic is “less than 1.0 new cases per day, per 100,000 people” and “less than 2.0% positive tests within the county”. For instance, right now in San Francisco, we are at a “Moderate” 3.5 Covid cases per 100,000 people, and 0.8% positivity, with 0 deaths over a 7 day average. Going in the right direction, but we are not out of the epidemic by California’s definition.
This is consistent with The Atlantic:
Crystal Watson, “a health-security scholar at Johns Hopkins University, suggested a threshold of 0.5 newly diagnosed cases per 100,000 people every day, and a test-positivity rate of less than 1 percent.”
Putting it all together: That means essentially, for the US as a whole, fewer than 2,000 cases a day, or 1/5 of what Fauci recommends.
So, here’s my feeling.
We are out of Covid epidemic as a country, when the daily case rate over the United States is somewhere around 5,000, and test positivity runs around 1%
That’s kind of midpoint of all the estimates I read. Likewise, probably when the daily test positivity rate is around 1.0%. In effect it will have settled at a level similar to the Flu. The disease will be considered “controlled”, as in “not growing unexpectedly”.
There still may be localized epidemics as happens with other diseases: “In South Texas there is an epidemic of Viral Meningitis at […] school” or “A breakout of Measles occurred in an unvaccinated school population in Vermont” but the country as a whole is not considered in an epidemic.
There are a number of messages which people seem to hanging on I want to also clarify from my reading, then on to forecasting:
[1] We’re NOT out of the epidemic when a specific number - 75%, 80%, 85% of the population is immunized. What I have read is that when X% of the population is immunized “we should see case rates drop dramatically”. The problem is that X% varies whether we’re fighting the “wild” form of the virus, or whether we are fighting one of a number of more communicable variants, and how vulnerable the community is to transmission.
[2] Vaccination alone does not get us out of the epidemic. Fauci and any number of other reputable doctors working in immunology reiterate that it’s critical we focus intently on what I’ll call “The six pillars” to accelerate departure from the epidemic: vaccination, testing, tracing, quarantine, masking, distancing. I’ve read many times in the last year, if we could simple get universal masking, or 3-4 million tests a day, or effective tracing, we possibly would have been able to hold the virus in control already.
[3] We may not get out of the epidemic status as a country with vaccination alone if the variants multiply quickly enough, particularly worldwide. It may take frequent, almost daily testing in with quarantine and tracing, in addition to vaccination, to drive case rates close to the 5,000 daily range. The local epidemics may still go on as variants continue to emerge. I do not read any forecast when that may end, if ever.
OK, so back to my original question “When is the epidemic over, and how do we know we are there?” I have an answer to the ‘how do we know’, but not to when. So let’s combine everything, with some forecasting.
There is widespread forecasting now of all components of COVID, particularly of fatalities and cases. I have my own private models I’ve shared on prior postings, which have generally been around 90% accurate over 6-12 week windows. What I don’t see in forecasting is the exit to epidemic status.
Let’s combine the “experts say” information with forecasts. Let’s take California for a moment.
If we hear:
Then
CA is currently, according to the CDC is at 17,265 cases/week, or 4x what would be considered epidemic level. (https://covid.cdc.gov/covid-data-tracker/#forecasting_weeklydeaths). Ok, but the CDC doesn’t forecast more than a week or two out in their model.
I’ll use the IHME forecast of cases then (https://covid19.healthdata.org/united-states-of-america/california?view=infections-testing&tab=trend&test=infections) instead of my own. IHME have become much more consistent than they were a year ago. I looked to their “Daily Infections” chart which projects cases, cases with universal masking, and worst-case estimates.
IHME would show that California will exit Epidemic status, as a whole, around May 18th. Here’s a snapshot from their “Daily Infections” chart for California:
Now that’s a day for celebration if trends hold. Interestingly, current projection and universal masking converge — whether that’s vaccinations or Californians “get it”, I won’t hypothesize. IHME doesn’t forecast positivity rates.
Unfortunately for the US as a whole, the IHME data don’t show a date when we hit the 5000 threshold – it does show that we hit what I’ll call the Fauci threshold of 10,000 around 25rd of June, which is perhaps why we hear of 4th of July as a day to celebrate “return to normalcy.”
So, I hope this was illuminating, and exciting. I’m a strange numbers person, and all of this meshed in my mind correctly to give me a much more positive hopeful feeling than I’ve had in months. I’ve not written specifically about Covid and forecasting for roughly 9-10 months now, since I forecast an explosion of Covid in “Red country” around 4th of June 2020, and found the entire exercise too depressing.
I do see the light rapidly approaching at the end of the tunnel, and in doing these estimates and calculations, I found I confirmed something which I and many friends ‘felt’ in San Francisco.
We have actually exited ‘epidemic’ status a few times already in March as the daily case count reached a low point sustainably. Exiting the epidemic is reachable. That, with the extension of vaccination to the whole adult population of California in the next two weeks (some counties already at that level), I’m able to relax.
A little. I’m not really a relax kind of person, if you’ve been following any postings. Cheers!
Stay Calm. Critical decisions need a clear head.
Stay Sane. Incessant COVID noise from deranged people will derange you.
Stay Home. There’s no safety in numbers, for the time being.
Disclaimer: I’m not a statistician, nor am I an epidemiologist or physician. I do have substantial training in science and mathematics. My assumptions are based on publicly available data, and interpreted without domain-specific expertise to temper my judgements.
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