The Second Wave of Covid-19 (updated 15apr20)

George Rebane

[A rewrite of this piece for broader audiences - 'The big decision and the second wave' - appeared in the 18apr20 online and print editions of The Union.]

As we start to turn the corner on the initial wave of C19 infections sweeping the land, people are already talking about the second wave and what it may look like after we carefully restart the economy.  I did some noodling with Epidyne about what a second wave might look like as it takes another cut at us in California.  Our state is thought to have had a large TBD fraction of people who already became immune last fall and early this year through asymptomatic infections.  This is plausible from what we now know about the 2019 timeline of the Wuhan virus.

This assumption goes a long way to explaining why California’s infection, morbidity, and mortality numbers are so low, especially since we are one of the major Asia gateways into the US.  The bottom line here is that we in our state already had developed a high level of herd immunity (q.v.) when the real C19 hit the country in early February of this year.

I ran a number of scenarios of a second wave using the latest CDC max reproduction rate of 2.6 which gets whittled down as herd immunity grows.  And everyone now says that the Germans have calculated the most accurate death rate of 0.4% of the infected for developed country healthcare systems.  Using these numbers on California’s 40M population, and letting the immunity fraction from the first wave vary from 0% (no one became immune) as an unrealistic bookend, to 50%, which most epidemiologists now think is closer to truth, I generated the infected population curves shown below.

The Epidyne model (here) illustrates the highly non-linear nature of epidemic spread experienced in populations with various levels of herd immunity.  We see the impact of the disease weakening as the percent immune increases in a fairly orderly way with little change in the second wave’s onset and its duration.  This begins to markedly change as the immune percentage passes 30%.  Then we see the curves flattening out with a delayed onset and a longer duration.  Keep in mind that the infected cohort is made up of the asymptomatic, pre-symptomatic, and those requiring professional medical attention.  The latter comprising of about 10% of the infected according to the latest figures.  It is also from this cohort that we derive the mortality numbers.

The table below shows the maximum infected, the maximum hospital load, and the number deceased for the second wave as a function of the initial percent immune.

From the graph above we see that the duration of the wave for the lower immunities is about 2.5 months, and for immunities above 40% the epidemic’s onset is later, of lower intensity, and lasts about 3 to 3.5 months.

We must also note that the above numbers don’t reflect any imposition of a second statewide quarantine.  Were we to take a more reasoned look at what kind of second wave we would have, I would agree with those who calculate that California’s immunity percentage would be very close to 50% coming out of the first wave that includes the cohort of pre-first wave immunities.  Of course, if a second widespread quarantine is imposed that impacted proportionately the uninfected vulnerable and immune populations, then the intensity curves would all be lower and also more spread out.

Important in all this policy making is the ability to conduct immunity (antibody/antigen) testing on random samples from the state.  I have extensively discussed testing previously (here and here), and also introduced readers to Epidyne (here).  And when all is said and done on running these numbers, it sure looks like we should be ready soon to loosen the reins on our economy, and then not be too apprehensive about the so-called second wave - it will be quite manageable.

[update]  So what all should policy makers actually consider as they wrestle with the decision of when and how to reopen the economy?  Items definitely to include involve and understanding of the scenarios I have illustrated above regarding second wave infections.  (We assume they have access to spread models at least as powerful as Epidyne.)  But before that, one needs to take a measure of the situation in answering the question, what is and/or should be the immunity level in the target population I’m considering opening up.  From above we saw that the immunity level should be somewhere north of 40% so that herd immunity can kick in and reduce the severity of the second wave after we have again started doing business in the land.

That decision will again involve another round of testing a random sample drawn from such a population.  This time the test will be for the presence of immunizing antibodies/antigens, and these tests will also have their own levels reliability expressed in their sensitivities and specificities.  More formally these are respectively the probabilities of test positive given the presence of the ‘antis’, here P⁺. and test positive when no ‘antis’ are present, here P^-.  I explained the whole process here, for those needing a review.

The remainder of this update has a couple of squigglies in it that makes it easier to read from this pdf - Download SecondWaveUpdate 

[15apr20 update]  The Epidyne second wave results shown above are now beginning to be described by prominent contagious disease experts and epidemiologists in interviews and columns that forebode ill if C19 returns to a population with a still WIP herd immunity.  They are now doing some Monday morning quarterbacking on the governments' policies of people quarantining, sequestering themselves at home, and social distancing on their infrequent forays to gather their necessaries (more here). Their arguments about “unintended consequences”, of course, make sense.  All epidemics burn themselves out primarily through the beneficial action of herd immunity among the survivors of the disease (else they just kill everyone infected).  But herd immunity is inhibited by premature and too comprehensive and longlasting quarantines.  This means that once the people are ‘released’, any residual contagious agents will necessarily reinfect and start the disease cycle all over again.  I have illustrated that with the Epidyne spread model, generating a number of epidemic return scenarios as a function of various levels of herd immunity being in place when society was opened up again.

Comments

[scenes]

"Important in all this policy making is the ability to conduct immunity (antibody/antigen) testing on random samples from the state."

It seems to me that if testing is purely to plan and monitor policy, you could probably stand to spend the time/money on more accurate forms, which no doubt exist. It depends on the cost v. the sample size needed for a desired accuracy of course.

Given the lack of rigor in all of this (hey, it's an usual situation after all, everybody is winging it), I think that the main low-hanging fruit in study will be by comparing countries after the dust settles. They are ready-made experimental labs with quite different situations and results.

I was just poking through the demographics and CCP-flu stats for Sweden and Finland, arguably similar (by world standards) in some ways, although the inhabitants would disagree. One with little response one with quite a lot. Sweden of course has that blessing of Third World immigration (praise be to the globalist gods) and you can pick out the demographics of Finland by language spoken. 2:1 difference in population. Urbanization looks similar. A pair of good experiments.

[scenes]

Speaking of rigor, I've been enjoying the 'journalists' filling up traditional news magazines with a valiant effort to tie intersectionality with CCP-19. Ain't nothin' better than a newschild pounding out magazine pieces combining bits of opinion and fantasy to help explain the world. Bummer that they don't know anything of which they speak, but The Atlantic readers don't care in any case.

No doubt the problem of cold fusion could be cracked if we simply had less institutional racism in the ranks of physicists, but that'll have to wait for a different day.

I do feel left behind though. If I could sit in a room with a pencil and notebook and no research materials or deep thought, it would be nice to just hammer out a bunch of personal musings as fact for a major league publisher. I wonder what the rate per word is.

[Don Bessee]

Good point -

https://www.breitbart.com/politics/2020/04/14/nolte-what-terrible-coronavirus-models-tell-us-about-global-warming-models/

;-)

[Bill Tozer]

Big tricky decisions are on the horizon. When do we go back to work? When do we take the kids to a Little League game or blow a week’s pay at a fancy restaurant to impress a further ex-wife?

These decisions are wrought will peril on many levels; social, political, economic, stress/mental health, Q of L, and much more. I don’t have the answers as the situation is fluid. Tough decisions lie ahead with damned if you, darned if you don’t scenarios.

VDH (from the Greater Fresno area)
‘We Are Approaching COVID-19 Gut-Check Time’

“Nothing about this epidemic was ever static. But we are on the verge of learning a lot more about the virus that will result in as much disagreement as relief.”

https://www.nationalreview.com/2020/04/coronavirus-testing-will-reveal-much-about-virus-lockdowns/
————————-
Pat Buchanan, never shy about his opinions on bigger issues, asks provocative questions.

What Price Victory — in the Coronavirus War?

https://buchanan.org/blog/what-price-victory-in-the-coronavirus-war-138432

[Bill Tozer]

Buck Sexton
@BuckSexton
·
1h
Those who shout down others with the cheap moral preening of “lockdown for as long as it takes!” are going to wake up pretty soon to a reality in which millions and millions of Americans without jobs or basic freedoms will just refuse to comply

https://twitter.com/BuckSexton/status/1250959318251376641?

[Gregory]

I think this link to folks getting huffy over Laurence Tribe's remark fits here
https://www.mediaite.com/politics/harvard-law-prof-laurence-tribe-under-fire-for-apparently-suggesting-mass-coronavirus-infection-and-death-to-solve-pandemic/

I think what Tribe was actually saying was spot on... the virus is here, we have to live with it. Like every other virus on the planet. As a relatively high risk person (65 and a touch of hypertension, treated) I do appreciate the Left wanting to trash the economy to keep me isolated from life (I really, really do guys, thanks) but the benefits to me are costing everyone more than I value them.

There may never be a vaccine... we won't know until there's a candidate that gets tested and found to work.

So, please, let's let things fall where they may. I won't go searching for a sick person to get a dose of possible death, I promise, and stay the F home if you're ill with something that might be transmissible.

I listened to Terry McAteer give a 'lecture' on the 1918 Flu pandemic today, and it struck me as expected, a sloppy hour of slideware suitable for an AP American "History" class but masqerading as a college experience, via "OLLI" at Sierra College. I doubt the scare of 1918 fits 2020... as in 1918 they didn't know about viruses AT ALL and didn't know the basics of how not to get a respiratory virus or how they spread.