Sci­en­tific modelling is valu­able – but remember the lim­i­ta­tions

The Guardian - - News Coronaviru­s - Ian Sam­ple

The lessons to be learned from the coro­n­avirus pan­demic are so nu­mer­ous they will keep schol­ars busy for decades to come. Chief among them is the value of modelling and the fact that an un­crit­i­cal re­liance on their find­ings can lead you badly astray.

A re­cent model from Ox­ford Univer­sity assessed how well dif­fer­ent out­break sce­nar­ios fit­ted the rise in Covid-19 deaths in the UK and Italy. The most ex­treme UK sce­nario as­sumed only a frac­tion of peo­ple were at risk of se­ri­ous ill­ness and es­ti­mated that, as of last week, 68% of the pop­u­la­tion had been ex­posed to the virus. The study, which has not been pub­lished or peer re­viewed, un­leashed a flurry of head­lines declar­ing that coro­n­avirus may have in­fected half the peo­ple in Bri­tain. That’s 34 mil­lion peo­ple.

But as infectious dis­ease mod­ellers and pub­lic health ex­perts, in­clud­ing the Ox­ford team them­selves, have pointed out, the model used as­sump­tions be­cause there is no hard data. No one knows what frac­tion of the pub­lic is at risk of se­ri­ous ill­ness. The study merely demon­strates how wildly dif­fer­ent sce­nar­ios can pro­duce the same tragic pat­tern of deaths – and em­pha­sises that we ur­gently need sero­log­i­cal test­ing for an­ti­bod­ies against the virus, to dis­cover which world we are in.

Paul Klen­er­man, one of the Ox­ford re­searchers, called the 68% fig­ure “the most ex­treme” re­sult and ex­plained that “there is an­other ex­treme which is that only a tiny pro­por­tion have been ex­posed”. He added that the true fig­ure – which is un­known – was “likely some­where in be­tween”. In other words, the num­ber of peo­ple in­fected in Bri­tain is ei­ther very large, very small, or mid­dling. This may sound un­help­ful, but it is pre­cisely the point. “We need much more data about who has been ex­posed to in­form pol­icy,” Klen­er­man said.

The modelling from Im­pe­rial Col­lege that un­der­pinned the govern­ment’s be­lief that the na­tion could ride out the epi­demic by let­ting the in­fec­tion sweep through, cre­at­ing “herd im­mu­nity” on the way, was more trou­bling. The model, based on 13-year-old code for a long-feared in­fluenza pan­demic, as­sumed the demand for in­ten­sive care units would be the same for both in­fec­tions. Data from China soon showed this was dan­ger­ously wrong, but the model was only up­dated when more data poured out of Italy, where ICUs were swiftly over­whelmed and deaths shot up.

It wasn’t the only short­com­ing of the Im­pe­rial model. It did not con­sider the im­pact of wide­spread, rapid test­ing; or contact trac­ing and iso­la­tion, which can be used in the early stages of an epi­demic, or in lock­down con­di­tions, to keep in­fec­tions down to such an ex­tent that when re­stric­tions are lifted the virus should not re­bound.

It is not a ques­tion of whether mod­els are flawed, but in what ways are they flawed. That does not make them use­less: mod­els can be enor­mously valu­able if their short­com­ings are ap­pre­ci­ated. But, as with other sources of in­for­ma­tion, they should never be used alone.

Newspapers in English

Newspapers from UK

© PressReader. All rights reserved.