Survival Index: A robust metric to estimate the health measures to fight COVID-19

Santanu Datta and Sreenath Rajagopal

April 08, 2020

Unlike the Dickensian metaphor, it is the worst of times, and the best of times is now a distant memory. The onslaught of COVID-19 has taken over the world, and most countries are stretched in its medical response. The degree of global spread and a given states/countries measures against the epidemic necessitates an essential to look at the epidemiological data carefully. The number of people who have been: infected, tested and people who have recovered or succumbed to the disease. Currently, the general trend has been to gauge the number of people infected as a metric for pursuing measures such as lockdown, mass testing, the sufficiency of hospitals beds and ventilators. Unfortunately, one of the key features that mask this metric is the testing numbers itself. Firstly, countries like South Korea and Norway have tested a maximum number of people (as a percentage of population) whereas, a populous country such as India could be one of the lowest. Thus, any statistical analysis or interpretation, which takes a daily or cumulative infected number, is fraught with erroneous conclusions. Secondly, COVID-19 has mainly been in ‘human congregated’ areas, especially, cities and anyone who is sick would undergo testing at the local hospital where a positive result would lead to his/her hospitalization.  A more enlightening alternative is calculating Survival Index (SI). It is the ratio of people recovered by the number of people who have died on a given day. This measurement is relatively independent of the population tested and is useful when a disease has become an epidemic. A higher SI indicates adequate hospital measure or a viral strain causing low mortality and a lower SI shows inadequate hospital measure and/or disease-inducing high mortality. Since many isolates of the virus are sequenced, one can gainfully test this hypothesis by taking two or more countries infected by the same virus strain and determine the Survival Index to ascertain the efficacy of the medical infrastructure.

We have evaluated the Survival Index of the G20 countries in a simple time-series plot in Fig 1. Data from the Kaggle database (Updated every day) was retrieved up to April 3, 20201 and used to determine the Survival Index. This was carried out for the G20 nations from 19th March 2020 to 2nd April 2020 (15 days). However, Canada had insufficient data and was not considered for this exercise.

It is seen that South Korea, which has successfully handled the pandemic, is on the top of the list followed by China and Japan.  However, the negligible standard deviation (SD) of SI (Table 1) on such complex human health variable as SI makes the data from China somewhat dubious. The SI value from other G20 countries has a consistent pattern, where the standard deviation is proportionately larger. The countries that are doing well with this index, even with large number of cases, are Germany and Australia. The high SI values probably positively indicate the health care facilities in these countries.

In contrast, powerhouses of the world, namely, USA and UK are inadequate in their national ‘measures’. Their SI values are close to 1, which indicates high mortality and/or suboptimal medical infrastructure. Nevertheless, the SI value of USA is increasing steadily and is currently at 1.6. Whether significantly low SI value in the economically stable countries is due to a more virulent strain or health infrastructure malfunction is uncertain at this point. Interestingly, the data from India has two distinguishing features. The relatively low incidence of COVID 19 has been associated with low volume testing. However, the higher SI value compared to US and UK might indicate that parameters such as 1: mean Indian temperature, 2: the BCG vaccination background2 and 3:  the identification of a mutant COVID in India that has micro RNA binding sites3 may all synergistically contribute to the higher cure rates and hence high SI value. 

We hope that the survival index (SI) as a simple metric can aid policymakers operating in a global and national platform to fight the ensuing pandemic efficiently.

Table 1: Survival Index of G20 nations (For Latest Table CLICK HERE)

Figure 1: Time-series plot of Survival Index (SI) (For Latest Figure CLICK HERE)

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  1. COVID-19 Complete Dataset (Updated every 24hrs). 2020.
  2. Vrieze J. Can a century-old TB vaccine steel the immune system against the new coronavirus?. Science 2020. DOI:10.1126/science.abb8297.
  3. Sardar R, Satish D, Birla S, Gupta D. Comparative analyses of SAR-CoV2 genomes from different geographical locations and other coronavirus family genomes reveals unique features potentially consequential to host-virus interaction and pathogenesis. 2020. DOI:10.1101/2020.03.21.001586.