How many have had #COVID19 in Delhi? What % of infections have been detected? What is the fatality rate?

A (longish) #thread on Delhi's epidemic, with some analysis of its three serosurveys + other data. Details in a technical document linked at the end. (1/11)
First, Delhi's current surge (which may be winding down) is real - not just about better detection. But the actual surge in infections has been considerably smaller than in June - detection has increased a lot, making it seem larger. (Similar story to Mumbai - more later.) 2/
Prevalence estimate: by mid-August between 37% and 49% of Delhi people had had COVID. By mid-September: between 43% and 60%. The wide range reflects many uncertainties. When the October serosurvey results are out, we'll know more. ( https://www.bloombergquint.com/coronavirus-outbreak/covid-19-delhi-governments-next-round-of-sero-survey-begins) 3/
Delhi's three serosurveys gave antibody levels of:
- 23% (July)
- 29% (August)
- 25% (September)

Interpretating the surveys is hard because of:
- poor transparency: no technical documentation
- changes in methodology & test-kit between surveys
- no sampling correction
4/
Detection of infections: to date, between 2.5% and 3.5% of Delhi's total COVID-19 infections have been detected. But at the moment it's higher: my estimate is about 8% of infections are currently being detected. (95% CI: 4-16%). Why is infection detection rising?... 7/
Fatality rate: Delhi's naive infection fatality rate (ignoring undercounting) is low:
- overall ~0.06% (95% CI: 0.05-0.07%).
- currently ~0.085% (95% CI: 0.04%-0.18%).
There is some indication that it has been rising - fourth serosurvey data will make this clearer. 9/
The approach (Monte Carlo) is to put plausible distributions on some of the many unknown quantities and run lots of experiments (10,000) to get distributions on prevalence, IFR, detection of infections, etc. (11/11)

Much more detail here: http://maths.mdx.ac.uk/research/modelling-the-covid-19-pandemic/delhiwaningantibodies/
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