What if it’s worse?
Every discussion regarding COVID-19 and our policy options has been based on a very important assumption: once you have got the virus and recovered, you are immune. It is for this reason that epidemiologists focus on a sufficient share of the population obtaining immunity from COVID-19 either by past infection or as a result of a future vaccine. If you do this, then even with normal physical interactions, the virus eventually dies out (as R0 becomes less than 1). In particular, this is why we can talk about HAVE and HAD testing as making people safe again. So, while the crisis is awful, the promise of immunity gives us hope.
What if that hope is unfounded? What if you are not immune even if you have contracted the virus? What if a vaccine is not possible for the same reason? In this case, epidemiologists no longer use the SIR (susceptible-infected-removed) model as there are no recovered people who are not able to infect others. Instead, we must use the SIS (susceptible-infected-susceptible) model. In that situation, when R0 exceeds one, the virus never goes away and a share of the population is always infected.[1] The only way to get rid of the virus is by extreme measures — for instance, socially distancing until there are no more infected people or by coming up with treatments such that we don’t care if people are infected or not.[2]
Is this outcome possible for COVID-19? Because the virus is relatively new, at the time of writing, it is hard to be sure. Scientists were optimistic that, because recovering from COVID-19 required antibodies that such antibodies would give immunity for some period of time. However, in April 2020, South Korea reported 111 of coronavirus patients testing positive again after they had recovered (and tested negative twice in a twenty-four hour period).[3] One possibility is that the negative tests were false negatives. Another is that the virus has reactivated. This is a virus that is latent for a time and but remains inside the cells of the host. This happens with chickenpox which can decades later reactivate in adults as shingles. Finally, there could be reinfection. This is why the flu is persistent. The anti-bodies only provide immunity for a time and not against alternative strains of the virus. Coronaviruses are a relatively recent phenomenon, so a lack of immunity remains a possibility.
Let’s take that worst-case scenario and presume that infected patients are not permanently immune. One implication is that HAD tests are of little value. Similarly, a vaccine will not be our saviour. Nonetheless, HAVE testing could be of value. While the intensity of testing would have to be even higher than what might otherwise be envisaged, the procedure of isolating those who test positive will reduce the ability of infected people to spread the virus around. In this situation, so long as this results in the rate at which those are being infected falling below the rate at which people are recovering for an instance of the infection, the pandemic can be contained, and the virus will eventually be wiped out.
This highlights another reason to invest in the testing economy. When it comes to HAVE tests, these are valuable whether the virus leads to immunity or not, or something in between. As a policy, they are a hedge against this uncertainty.
[For more on this, please see my book, Economics in the Age of COVID-19, now in pre-print, to be published soon by MIT Press]
[1] That share is (R0–1)/R0. So, if the R0 for COVID-19 is greater than 2, at least half of the population will be infected at any given time.
[2] See Robert Rowthorn and Flavio Toxvaerd, “The Optimal Control of Infectious Diseases via Prevention and Treatment,” mimeo., Cambridge, 2017; for a discussion.
[3] Park Si-soo, “South Korea confirms 111 cases of coronavirus reinfection,” The Korea Times, 12 April 2020 (https://www.koreatimes.co.kr/www/nation/2020/04/119_287752.html). There were also similar cases reported in Shenzhen and Wuhan China.
