ABC for COVID spread reconstruction

A recent Nature paper by Jessica Davis et al. (with an assessment by Simon Cauchemez and X from INSERM) reassessed the appearance of COVID in European and American States. Accounting for the massive under-reporting in the early days since there was no testing. The approach is based on a complex dynamic model whose parameters are estimated by an ABC algorithm (the reference being the PLoS article that initiated the ABC Wikipedia page). Results are quite interesting in that the distribution of the entry dates covers a calendar as early as December 2019 in most cases. And a proportion of missed cases as high as 99%.

“As evidence, E, we considered the cumulative number of SARS-CoV-2 cases internationally imported from China up to January 21, 2020″

The model behind remain a classical SLIR model but with a discrete and stochastic dynamical and a geographical compartmentalization based on a Voronoi tessellation centred at airports, commuting intensity and population density. Interventions by local and State authorities are also accounted for. The ABC version is a standard rejection algorithm with distance based on the evidence as quoted above. Which is a form of cdf distance (as in our Wasserstein ABC paper). For the posterior distribution of the IFR,  a second ABC algorithm uses the relative distance between observed and generated deaths (per country). The paper further investigates different introduction sources (countries) before local transmission was established. For instance, China is shown to be the dominant source for the first EU countries impacted by the pandemics such as Italy, UK, Germany, France and Spain. Using a “counterfactual scenario where the surveillance systems of the US states and European countries are imagined to operate at levels able to identify 50% of all imported and locally generated infections”, the authors conclude that

“broadening testing specifications could have considerably slowed the pandemic progression, buying considerable time to prepare mitigation responses.”

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.

%d bloggers like this: