Contact Tracing for COVID-19 Cannot Work
By: Bj Campbell
Tags: Economics, Medicine, Random, Covid 19, Coronavirus

Herd immunity is the only path, if we believe the math.

One common argument that crops up over and over in the COVID-19 discussion, when it comes to whether and how to come off of government mandated lockdown, is contact tracing. This argument states that we should stay on lockdown until our case numbers are low enough, and our testing capacity is high enough, that we can trace all contacts of people who are confirmed to have the disease, and test them, and then have them quarantine, and then test their contacts, and so on, so we can leave the house and behave normally again. And we only have to sit in quarantine long enough that these two numbers get to the point where our cases are low enough, and our testing capacity is high enough, that we can pivot to this other method of disease management.

I really wish this could work, but it can’t.

Advocates of this argument point to South Korea, which is successfully managing COVID-19 in this manner. What they don’t seem to understand, is that South Korea has a lot more tests than cases. What matters for this method is not how many tests you have, nor even how many tests you have per capita, but rather how many tests you have per infected person. South Korea, as of April 21st 2020, issues about 10,000 tests per day when running this method, with only around a tenth of a percent of tests coming back positive of late. They’ve only had around 10,000 total confirmed cases. They’ve tested around 500,000 of their 51 million population, but they had high testing capacity early and could test everyone who had contact with a confirmed case.

How Many Tests Do We Have?

The USA testing effort is plateauing at around 150,000 tests per day.

Only around 10,000 of these per day currently come from public sources and the CDC, the rest are private entities, many of which were prevented from entering the testing effort by the FDA until the middle of March.

Notably, our testing capacity is not climbing to meet that million tests per day number. It’s flattening out. And we are not using our tests in contact tracing. We are using them clinically for people who are symptomatic.

How Many Tests Do We Need?

This is harder to guess at. If our goal is simply to use our tests clinically, then we don’t need too much more than we have now. But if we want to use them in a contact tracing effort, to track down everyone who has this before they end up needing a doctor or infecting someone else, we need many, many more.

If we ballpark it using South Korea as an example, we’d need as many tests per day as we have total confirmed cases over the life of the virus. Around a million tests per day. Seven times as many.

If we presume many current cases aren’t counted, which is undoubtedly true, then that number could be higher. A recent Santa Clara County seroprevalance survey thinks that number may be 50 times higher, but it’s come under attack and may not be a good indicator. If we think they’re only overestimating by a factor of ten, then we’d still need five million tests a day.

If we back our way into the number of tests we need for contact tracing from scratch, as the Harvard Edmond J. Safra Center for Ethics did, we need 30 to 50 million tests per day. They estimate possibly 100 million. That’s an insane number in a country of 340 million people, but that’s the prediction, and the reason why is clear when you unpack what they propose:

Find a positive.

Test everyone they came in contact with in the last six days.

If any of them test positive, repeat.

In that scenario, you may be forced to get a test several times a week even though you exhibit no symptoms purely because you were at the bowling alley with someone else who tested positive. And so on.

So depending on who you believe, we need between seven and three hundred times more tests than we have to be able to do “contact tracing” for COVID-19. And according to one popular narrative, the country must stay in quarantine until this capacity is reached. And our testing capacity isn’t currently climbing.

Wait For The Vaccine!

A vaccine will take between 12 and 18 months.

After around a month and change of our current quarantining measures, we are dumping 5% of our nation’s milk on the ground, a number that is soon to double, destroying over 5% of the total egg production, destroying tens of millions of pounds of fresh food, 25% less beef is being produced, and the CO2 for drinking water treatment may be cut to 33% of normal. These are first order effects due to nothing more than supply chain disruptions. More first order effects are sure to matriculate, and combine, into even more severe issues for the critical economic infrastructure of the country. Unemployment aside, and inability to pay for critical medical care aside, and inability to pay for a mortgage aside, we will end up with mortality related to food shortages under any plan to maintain our currently broken economy for a year or more. And that could lead to the 3rd order effect of civil unrest. Waiting for a vaccine is simply not on the table.

Herd Immunity is the Only Way

Many advocates of “flattening the curve” seem, in recent weeks, to have forgotten the whole point of flattening the curve. The point of the exercise is to run the hospitals as close to capacity as possible to ensure a specific subset of infected people get treatment: those who would die without it but would live with it, while making sure that the general population catches this disease at reasonable rates and moves on from it.

If you flatten the curve so flat that nobody gets infected, then you’ve failed to flatten it at all. You’ve just pushed the curve to the right, and it happens after quarantine is lifted. If you flatten the curve so that ICUs run at 50% capacity, then your quarantine lasts twice as long as if ICUs run at 100% capacity. If you know by your medical experience that 50% of the people you take in are going to die no matter what you do anyway, you can triage those (send them home) and run a 100% capacity ICU in a third of the time as the hypothetical 50% capacity case. Your goal is to save the people who can be saved. Anecdotes I’ve read seem to indicate that this decision is difficult to make, because the disease progresses quickly in those who die, and seems to not make that final jump in those who are effectively treated. We may not be able to make truly informed triage decisions unless we do them by age or comorbidity factors, which would be an ugly procedure.

Early discussions, including ones here on HWFO, were about how to get the curve flat enough so that we were reducing triage to acceptable levels. With states approaching COVID-19 death rate peaks without full ICUs, they are only prolonging quarantine by maintaining it without a full ICU. And curiously, given how “flat curves” are “longer curves,” they are prolonging the long term exposure of their healthcare workers to COVID-19 as well, increasing the death rates of healthcare workers in the long term.

This does not mean that the gates should be thrown open without a plan, nor that the plan should stress opening bowling alleys and salons over restaurants. But any state under ICU capacity with a relatively flat deaths per day rate should absolutely ease restrictions, continue to quarantine the old, infirm, or those with comorbidities, let healthier people get sick, and move towards the only possible answer, whether we like that answer or not.

The other answers aren’t answers at all, mathematically speaking.