had the virus, R0 drops below one because there are no longer enough susceptible people to infect. The simple animation below shows how this works. To reach herd immunity, you need upwards of 70% of the population to be immune. This is typically achieved with the seasonal flu each year because about 62.6% of the US population gets the flu vaccine. However — with COVID-19, letting it race through 70% of the population at its current trajectory is not a good outcome for the healthcare infrastructure. This was modeled extensively by Imperial College London in a study many readers may have already seen. Doing the simple math: assuming a 1% mortality rate and 70% of Americans infected, the result is 2.3 million deaths.
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Breaking the chain of transmission
Timeline estimate: 2–3 months
Stopping transmission of COVID-19 is easier said than done. Barring a fortuitous mutation that lessens the infectivity of the virus, it is incumbent upon society to stop the transmission. With treatments and a vaccine in the distant horizon, and the specter of overwhelmed hospitals looming, we have no other choice.
This is the realization by governments worldwide as each embarks on drastic social distancing programs to curb the spread of COVID-19. Fortunately, we’ve been given the blueprint on how to control an outbreak by Singapore, Taiwan and South Korea.
Lower R0 through social distancing. Whereas the flu enacts its own form of social distancing — you know it when you get the flu, it glues you to your bed for a few days when you’re at peak infectivity — COVID-19 is insidious in its long latency period and mild or completely asymptomatic cases. Studies out of China, Singapore, and Italy have found that 86% of infected patients were undiagnosed, 50% of new cases could be attributed to asymptomatic contacts, and 50% of COVID-19 positive patients were completely asymptomatic. While social distancing lowers R0, it cannot be maintained forever due to its severe economic impact. More importantly, social distancing alone is not sufficient as long as there are undiagnosed, asymptomatic carriers still spreading the disease.
Support the healthcare system through the initial wave of cases. The goal of social distancing is the flatten the curve to prevent pushing our healthcare system past the critical threshold of ICU and ventilator capacity. The need for ICU space, ventilators, and the even more pressing issue of inadequate personal protective equipment (PPE) has been covered extensively elsewhere.
Testing and contact tracing. There will come a point when the number of new daily cases and deaths are tapering off and the economic pain of social distancing becomes too great to bear. At that point, society must re-open for business. What happens at this juncture will be critical to prevent relapses into cycles of repeated social distancing measures. This was covered expertly in Tomas Pueyo’s article entitled “Coronavirus, the Hammer and the Dance.” Specifically, I am referring to the “the dance” portion of the pandemic response. The key here is that we must establish a testing and contact tracing infrastructure to identify and quarantine infected individuals, asymptomatic carriers, and all their contacts. The practice of contact tracing is tried and true — it is how local health authorities handle every case of tuberculosis. I should point out that Singapore and Korea have thus far avoided drastic lockdown or social distancing measures. How? By testing widely and rapidly to stay ahead of the disease and keep at-risk individuals strictly quarantined.
What happens when we loosen the restrictions on social distancing will determine whether we can put COVID-19 behind us, or whether it will roar back in cycles of region-by-region lockdown until we achieve one of the first three options I presented. As domestic and international travel resume, there will be localized cases of COVID-19 for months to come. The challenge before us is this: can we contain these individual ripples before we face another tsunami?
We must persist towards a return to normalcy by sheltering in place and fighting back the initial surge of cases. All the while, we must be committed to building a national public health infrastructure capable of widespread testing and contact tracing. In time, treatments and a vaccine will be developed, COVID-19 will be defeated, and we will teach future generations the lessons we have learned along the way.
- Then tragedy struck the love birds on a rainy April afternoon in 1906. Pierre was crossing a street when he was run over by a horse-drawn carriage that was carrying six tons of military uniforms. Pier