Herd Immunity or Containment through Test and Trace?

Coronavirus Disease 2019 (COVID-19), a viral disease caused by the virus SARS-CoV-2, has arrived and is spreading in Hawai’i.  In an attempt to “flatten the curve,” we have closed schools and many workplaces, while the entire state shelters at home. As a result, the economy is contracting fast.  While sufficiently flattening the curve is the most critical concern, what happens next? What is the exit strategy from current shutdowns and social distancing? We contemplate two alternative strategies and discuss how Hawai’i’s unique characteristics may factor into the State’s decision.


11 thoughts on “Herd Immunity or Containment through Test and Trace?”

  1. It is reassuring to know that experts are thinking about an exit strategy to this pandemic. How might the choice of an exit strategy or the efficacy of the choice be affected by the fact that restarting Hawaii’s economy is dependent upon tourism (i.e., the influx of travelers who may well be carrying the virus)?

    1. Michael Roberts

      Linda, thank you for your comment. If we take the “test and trace” approach and attempt to truly contain the virus, we will be in perpetual risk of reinfection from tourists. We can attempt to screen, test and trace tourists too. This will likely require special protocols. In time, hopefully, there will be treatments and/or a vaccine. We can probably learn a lot from other countries that appear to be successfully navigating these issues (Singapore, South Korea, Hong Kong), but none of them are as dependent on tourism as is Hawai‘i. While screening, testing, and tracing will involve substantial costs, the benefits are almost surely much greater.

  2. Wouldn’t we want to analyze this at the margin? Marginal benefits to each ppt reduction in R0 are huge until R0 < 1, then we're past the curve's peak and heading toward zero COVID cases. You seem to concur that the marginal costs of current HI policies are outweighed by the marginal benefits, so do you think this is the most effective/efficient way to get below one, or do you think one of these exit strategies could have been employed earlier and resulted in a better marginal benefit/cost ratio? If the latter, why propose these as exit strategies and not strategy pivots?

    Also re: testing, despite the public/private differences in testing (are the public testing requirements truly necessary, or necessary like the FDA/CDC regulations that prevented greater/earlier testing?) what are your thoughts on group testing in HI as outlined Cochrane and, more recently, Kotlikoff?

    Mahalos for sparking the discussion.

    1. “Weighing benefits against costs is the way most people make decisions — and the way most businesses make decisions, if they want to stay in business. Only in government is any benefit, however small, considered to be worth any cost, however large.” – Dr. Thomas Sowell, April 6, 2020.

  3. Michael Roberts

    Thank you for your comment.

    Yes, I think it’s clear from any back-of-the-envelope calculation, using conventional measures of the value a statistical life, that the shutdowns are worth it. A recent survey of top economists, writing about the national situation, were unanimous on this point. And this study from the University of Chicago does a bit more work to sketch out the benefits and costs on a national scale. https://bfi.uchicago.edu/working-paper/2020-26/

    The challenge with decisions at the margin right now is that we have such poor information on the current state of the virus (I’m hopeful, but we don’t know) and how various measures affect its spread. There might be a role for so-called adaptive learning: (1) get basic mechanisms for test and trace in place; (2) gradually open the economy in a way that maximizes the benefit/risk ratio; (3) evaluate the benefits and how spread increases; (4) adjust given what we learn. There’s some economics here, but there’s even more epidemiology, and technical and logistical questions about how well test and trace, face masks, and various forms of distancing rules work to reduce the spread of the virus.

    The encouraging thing is that a zillion people are working on these questions at a furious pace. I think we’ll know enough to make some sensible, incremental decisions soon. I worry most about getting the legal and logistical mechanisms in place to make it happen. I think we’ll have plenty of testing and an appropriately low level of disease incidence long before we have the management systems ready to go.

    1. Agreed re: the lag in legal/logistics management, which is kind of my concern really. I’m accustomed to the OODA process but public and private reactions thus far strike me as Act first and maybe do everything else later. I’m risk averse so I’m inclined to believe it’s for the better, but we really don’t seem to know. Especially after the recent study of COVID research finding a prevalence of low power and high bias, being forthright with assumptions and models seems very important. But like you said, that’s also reason for encouragement given the sheer amt of data science/analysis/viz/study being thrown at this challenge!

  4. Andrew R Walden

    Some countries such as Japan and Taiwan are getting close to knocking Corona down. Micronesia so far hasn’t had any Corona. Those might be candidates for an early reopening of air travel once Hawaii has knocked Corona down to their satisfaction. Japan of course is the big tourism prize in this scenario.

  5. Great discussion on this so far. I wanted to add my two cents.

    I agree! it is too soon to know how Hawai’i will fair in the coming months. In 1918, Denver, Colorado imposed gathering restrictions to limit the spread of the flu. As cases dropped, they felt they were past the peak of the pandemic and loosened restrictions. The result was a second peak and a bimodal distribution overall. A double whammy on lives, hospitals, and the economy. The lesson to be learned is that sustained investment in continual monitoring to contain through test and trace will go far to protect the economy and must be part of our exit strategy. No exit strategy should go without heavy investment in monitoring (test and trace), private and public. No matter the cost, monitoring is the finger on the pulse that will supply the data for leaders to make informed decisions.

    Herd immunity is not a strategy, it is an inevitable end for our species. Flattening the curve is about how long it takes us to get there. Rapid herd immunity means mass graves and overwhelmed hospitals. Slowly building herd immunity will save lives but depress the economy longer. There is no way around it as a vaccine is no where in sight. Cities, States and Nations must find the balance in building herd immunity without overwhelming hospitals. This is no easy task as the brief points out, many of Hawai’i’s low-income households are made up of multi-generational families. This means if social distancing restrictions are loosened for the youth, the keiki will take it home to the Kupuna. This will therefore disproportionately impact low-income families. Hawai’i will need smart implementation, maximum flexibility and heavy monitoring at airports, schools and hospitals to find which social distancing measures can be relaxed and which should stay in place.

    Another point I will make, begins with the vision residents and politicians have for the islands. Not just in terms of the economy but holistically. Clear vision of the future will drive future decisions in investment. With the economy down, this is an opportunity to restructure and diversify to tackle problems that existed pre-pandemic. With Hawai’i heavily dependent on tourism and no return to normalcy in the near future, many residents are without jobs. National estimates of unemployment caused by CoVid19 can be as high as 20-32%. I assume, with such dependency on tourism and the food and beverage industry being the State’s largest employer, Hawai’i will be on the high end of those estimates if not higher. Putting those individuals back to work will be a challenge for the State. Massive investments into public schools, green infrastructure, and agriculture will diversify Hawai’i’s economy and increase resiliency against future economic disruptions.

    Investing in k-12 public schools as well as higher education will benefit teachers and administrators in the short-term. Investments would allow public school to build the online infrastructure needed for remote schooling. Post- pandemic, better schools will be more attractive (or at least less repulsive) to outside professionals, and an educated workforce will attract future businesses. Investments in green infrastructure will provide jobs in the short-term, on the job training will lend skills to otherwise unskilled workers currently unemployed, and increase productivity overall for sustained long-term growth, better positioning Hawai’i in the nation’s economy. Green infrastructure will also help protect the natural beauty and landscape that attracts so many tourists, when we overcome this pandemic. Finally, the governors decree to double food production in the islands should be backed by actual investments disbursed by HDOA and directed by the legislature. As many of you may know, Hawai’i imports around 85% of all food consumed. A dated study by the office of planning estimated in 2012 that increasing local food production by just 10% could keep over $300 million/annually in State. If the savings are then reinvested, long-term growth and prosperity could become a reality. The green infrastructure along with smart legislation would help protect Hawai’i’s natural and cultural resources from the environmental externalities of agriculture.

    An exit strategy and vision that incorporates the points above will 1) allow us to closely monitor infection levels and apply an appropriate response that is neither wasteful or costs lives; 2) allow for the continued schooling of our keiki during the pandemic and better prepare them to be competitive post-pandemic; 3) offer opportunity for the now unemployed in construction jobs rebuilding our infrastructure, protecting our cultural and natural resources, and improve the overall productivity of the State; 4) increase resiliency, decrease food insecurity, and save the State hundreds of millions of dollars annually while creating jobs.

    I believe these measures will better insulate the Hawaiian economy from future disruptions, including pandemics. What are your thoughts?

  6. First exit strategy sounds too far from conventional wisdom for leaders to contemplate, even if optimal. Infect the young people fast (and keep enough of them away from older people)? Maybe a bunch of modern-day Woodstock events? Once they recover, they can go out and run the economy. Controversial part is that the same number of people get infected with and without mitigation.
    But according to the Charles Murray study, mitigation results in less people getting infected (by Aug 4 in his graph when infection rate is very small). The trouble is that we don’t know just how strict test-trace-contain must be to be effective.
    There is a risk that lax enforcement of containment leaves you in between the two idealized exit strategies and you pay the cost of containment without getting the benefits. Getting the test results back faster would help in the assessment. Is that about to happen?

  7. Michael Roberts

    Andrew, Dain, Jim,

    Thank you for the thoughtful comments!

    A few things to note since posting:

    1) We have a lot more confirmed cases, but we also have over 10,000 tests to date. Sadly, we’ve had our first death, too. The number of confirmed cases relative to both deaths and hospitalizations suggests that we are either identifying a large share of our actual cases or there have been some false positives (not a concern in most places), possibly a bit of both.

    2) Here is a really nice interactive epidemic calculator that can be used to project things going forward. If I try to calibrate to Hawaii, I come up with much fewer deaths than other projections (assuming we stay sheltered at home) (~25 versus projections of 400). I think the projections that others are using are empirical and use confirmed cases to calibrate the model, not hospitalizations and deaths–this is the key reason I believe (hope?) that they exaggerate our current projected mortality. It’s obviously trickier after we open up. This interactive model is really useful to gain insight into the epidemiological modeling (or, it has been for me). We may try to post a special Hawaii version here at UHERO.

    Link: http://gabgoh.github.io/COVID/index.html

    3) Many experts do seem to think that test and trace is no longer feasible, and herd immunity is our only option, although they are probably not considering Hawai’i’s specific circumstances. And I think they may underestimate what we might do with technology and rapid crowd-sourced response. While it is a grim prospect, I don’t think herd immunity is quite as grim as Dain suggests, so long as it were managed carefully so as not to overwhelm our hospitals (admittedly difficult): even with 1% mortality and 70% infection, about 10,000 would die. If uninfected 30% were the elderly and vulnerable, it might be much less. For perspective, about 5,000 die here each year from heart disease and cancer, combined. No doubt: this would be devastating, but not the end of our species. (I am *not* advocating that we take this route.)

  8. As I like to say, biology doesn’t behave.

    The epidemic calculator is excellent. It was set on about 87% of the population being susceptible. Generally speaking, the virus will spread to all of them until there is a vaccine or herd immunity is achieved (in theory defined as 50-60% of that 87% who are susceptible, exposed, recovered and immune).

    Flattening the curve is about not overwhelming the infrastructure at some point in time, ostensibly at the peak of daily new cases.

    Mitigation is necessary and effective in flattening the curve and does not require any testing, per se. Mitigation includes spatial distancing, masks, hand washing, effective use of disinfectants, improved sanitation, public education about transmission.

    I would say mitigation for the population at large does NOT include testing and tracing. It is impractical in this large country to test everyone.

    For defined sub-populations, though, diligent testing and mitigation is vitally important to protect them long enough until a vaccine is developed, or treatments are better, or transmission (including asymptomatic carriage) is understood better, or whatever it takes to protect them otherwise.

    Targeted testing delivers the biggest bang for the buck, regardless of the sensitivity or specificity of the test (of course, the better the test the better the strategy works).

    In no special order, first, we need to protect people who live in closed and dense populations like nursing homes, prisons, military encampments, cruise and military ships, et al. Seeding and spreading infection in these places is like a wildfire in dry forest. Second, we need to protect people whose work requires them to come and go to these closed and dense places. Third, we need to protect our health care workers who are essential to manage the infrastructure of the curve we are flattening. Fourth, we need to protect the food, sanitation and housing supply chains, who are essential to manage the infrastructure of the curve we are flattening.

    Society gains the most by testing these defined populations and isolating those testing positive until they have protective antibodies and can return to their prior roles. This strategy requires testing asymptomatic people (25% of whom, it is estimated, can be infectious). This strategy requires testing and re-testing those who initially test negative.

    Please see also the excellent article by Gabriel Leung, epidemiologist and dean of medicine at the University of Hong Kong: https://www.nytimes.com/2020/04/06/opinion/coronavirus-end-social-distancing.html

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