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Let’s talk suppression versus eradication. The real expert here is probably @devisridhar and she can chime in if she wants. As far as I can see we face several obstacles to properly evaluate an elimination option. 1/16 #EconTwitter #EpiTwitter https://twitter.com/_maia_king/status/1323655994405257216
First, it seems almost impossible to do and astronomically expensive. In history, only smallpox has been eradicated https://www.nature.com/scitable/blog/viruses101/smallpox_the_most_talked_about/ This is THE shining example we can point to in terms of eradication and it took an enormous amount of effort and coordination. 2/16
The classical paper on the economics of this achievement is Barrett (2007) https://link.springer.com/article/10.1007/s11127-006-9079-z 3/16
It should also be pointed out that many things conspire against eradication. First, we have population growth. This means that unless there is vertically transmitted immunity (mother to child), then new susceptibles will keep replenishing pool of susceptibles. 4/16
Second, immunity may wane over time, as experience with related vira shows. How fast it wanes and how infectious people become second time around is yet to be determined. But odds are that significan herd immunity is unrealistic. 5/16
Third, we may get vaccines. Will this sort the problem? Unlikely. It will help, but not necessarily eradicate the disease. There are many reasons for this. 6/16
(i) vaccines are not perfectly effective; see e.g. https://www.cdc.gov/flu/vaccines-work/vaccineeffect.htm to get an idea (ii) vaccine efficacy also wanes over time (vaccine is “leaky”) (iii) vaccine coverage is often incomplete. Plan for U.K. is for half of population to get it https://www.independent.co.uk/news/health/coronavirus-vaccine-when-uk-population-age-b791949.html?amp 7/16
For an overview of the Economics of Vaccination see Chen and Toxvaerd (2014) https://drive.google.com/file/d/1RlnKjyc2WfNulm42HN3wzhHaYj5SGf6_/view?usp=drivesdk 8/16
To hammer home the point, many vaccine-preventable diseases are endemic, such as measles https://www.who.int/news-room/fact-sheets/detail/measles 9/16
Indeed, recovery from measles confers permanent immunity yet the disease is endemic. So immunity and vaccines may not be enough. Treatments may help as we explored in https://www.inet.econ.cam.ac.uk/research-papers/wp-abstracts?wp=2013 10/16
To change tack somewhat, much of the modelling apparatus used by economists and disease modellers to do cost-benefit analysis is not quite right for studying eradication. This but is technical so here I flag an off ramp for those uninterested in mathematical modelling. 11/16
The standard compartmental models in epidemiology postulate a very large (continuum) population. In such models, eradication cannot typically be achieved in finite time, only asymptomatically. Even if prevalence decreases over time, it never reaches zero. 12/16
This is related to the famous “atto-fox” problem in population dynamics (meaning 10^(-18)th of a fox); see e.g. http://arima.inria.fr/020/pdf/vol.20.pp.95-125.pdf 13/16
There are two ways out of this: (i) one is to do a short-cut and assume that when prevalence fall below some exogenous threshold then the disease is declared eradicated. I’m not too keen on this approach as it’s somewhat ad hoc. 14/16
(ii) second approach is to introduce stochasticity into the dynamics. Then eradication can be achieved probabilistically. This is probably the right way to go, but most seem reluctant to give up the elegant deterministic dynamics of models without aggregate uncertainty. 15/16
To conclude, I think more work is warranted. Just saying it’s hard to achieve eradication’s and expensive is not addressing the question of how to value this option. Eradication, if it were achieved, would bring enormous benefits to society, as our current lockdowns show. 16/16
