While the world has been witnessing rapid transmission of COVID19, cases in India have only started to increases towards the end of March. This is largely due to inward flow of people flying back from Asia, Europe and North America.
Large numbers of people have quietly made their way into the metro cities and smaller towns from overseas following a spike in cases just before the lockdown. Following the lockdown announced in India just over a week ago, the migrant labour also started to rush back to villages in packed trains and buses, while many walking back hundreds of kilometers.
At this stage, no one has a clear estimate of the transmission rate happening within India. A lot has been written about it but no real attempt has been made at forward projections of transmission of infections, resulting hospitalisations and mortality within the population.
My objective in building a simple mathematical model based on existing facts is to understand the transmission of the virus in the population, the number of people who would end up in hospitals and those we would unfortunately lose in the battle against Corona virus.
I have made some very basic calculations from the rate of change in transmission of the infection globally and in India. The second data set, I have used is the number of deaths both globally and in India. The primary data has been sourced from World Health Organisation.
My methodology involved assessing the March data of patients and mortality. Analysing it over a 5 day period and calculating the growth rate which I then average to get the base rate for projecting the transmission in India over the next two months.
My findings are shown in the figures below and explained.
Figure 1- Global Transmission of COVID'19 Infection during March '20
There has been an exponential growth of patients globally suffering from COVID19 during the month increasing from 87,137 infected on the 1st of March to 6,93,224 infected on the 30th March. The corresponding increase in mortality in this period was from 2,977 deaths on the 1st of March to 33,106 deaths on 30th of March.
Performing calculation over a 5 day period in the month of March, this yielded an average infection transmission rate of 43.4% and an average mortality rate of 4% in patients suffering from COVID19. These rates would differ if examined in greater granularity by world region, demographics and conditions.
It is remarkable to note that the transmission rate grew consistently over the period of March while slightly slowing down in the last 5 days. The rate of mortality grew from a low of 3.4% to 4.8% in the last 5 days of March. There would be much to debate on the causal factors for these numbers. The pandemic epicentre was China early March and has gradually moved Westward later in the month.
Figure 2 - COVID19 Transmission in India during March '20
Various agencies have derived rates differently. Indian express took a factor of 1.7 while most other modellers are using various numbers between 2 and 3. In the viral stage of transmission this rate will be much higher that what most modellers are using. Therefore the estimate remains conservative.
The mortality rate in India last month is by far negligible as compared with other highly impacted COVID19 countries. It was zero death on the 1st of March and has grown to 29 deaths by the end of the month. This corresponds to an average mortality rate of 2.1% calculated over 5 day periods for March. That effectively means 21 deaths per 1000 cases of transmission. The mortality rate in India is nearly half of the rest of the world. This is very likely to increase as we start to progress through stage 3 of the pandemic in India.
It is notable to mention that our transmission rate is higher than the global average for the same period while our mortality rate is lower. This may imply that more people will be infected than those who will succumb to COVID19 it as compared with rest of the world.
Figure 3 - COVID19 Projected Transmission during the period of March '20
The transmission projection begins with a base figure of infections as they stand on the 1st of April that is 1250 cases. A transmission rate of 2.3 has been used for cumulative progression over a 5 day period. The projection was calculated up to the 30th of May. This is anticipated to be the most intense growth of COVID19 infections in India. A peak of 3,92,54,565 infectious cases has been projected if there is no break in the cycle of transmission. A conservative transmission rate has been estimated compared with other modellers given the high density of population and demographic spread.
The unbroken infection chain if not adequately checked will explode towards the end of April resulting in a huge number of people infected in the community. Explosive and exponential growth of infections will occur should strict social distancing norms not be followed.
Figure 4 - COVID19 Projection for hospitalisation and critical care in India
The projection for hospitalisation and critical care requirement for COVID19 patients is based on the derived rate of transmission of infections as shown in the previous chart. Two other assumptions based on international practises in modelling have been included. The first assumption is that 15% of the transmission cases will require hospitalisation. The other factor is 5% of the total cases will require critical care at hospitals.
The figure 4 above shows an exponential growth through rapid community transmission. An unbroken transmission chain would result in cumulative hospitalisation of 58,88,185 patients infected with COVID19 by the end of May 2020. The sub-set of the admitted patients requiring critical care would rise to 19,62,728 by the end of May 2020.
Both these are staggeringly large numbers and our healthcare system is ill prepared to deal with the overwhelming requirement. The unbroken chain of transmission of the virus would result in tremendous stress on the health care infrastructure. The stress is expected to increase between the first and the second week of May. The system would be overwhelmed thereafter and will require extra resources to cope with the growth of critical patients, thereby implying new critical care field hospitals should be designed and commissioned. The preparation for which should begin in earnest now.
Figure 5 - COVID 19 Projected Mortality in India
The projection of mortality from COVID19 has been based on the derived mortality rate from March and base number of 32 deaths on the 1st of April. A mortality rate of 0.021 has been applied. An exponential growth of morality in COVID19 patient cases is expected to correspond to the increase in hospitalisation of infected patients. An unbroken rate of transmission of the virus would sharply increase the mortality between the first and second week of May.
There are a whole host of causal factors that may change this rate of transmission and improve the rate of recovery. The most vulnerable will be the elderly, children, pregnant women, adults suffering from malnutrition and patients with other non-communicable diseases. Preventive measure such social distancing, hygiene, sanitation, testing and containment of patients, availability of personal protective equipment, disciplined clinical management, and limiting relapse in patients. The long term defence is of course a vaccine which may not be available for another 18-24 months.
We can only hope to avoid this scale of tragedy in India by breaking the chain of infection. This requires a very serious commitment by the entire society. We must entirely avoid any kind of congregation where multiple social interactions can take place. We must take due care in maintaining high level of hygiene and sanitation in our immediate environment.
In the absence of a strong healthcare system, our only hope of averting a catastrophe is by limiting the transmission to under 3% of our national population of 1.3 billion (130 crore). The transmission chain is expected peak in May 2020. The peak may come sooner should we conduct ourselves in a discipline manner. The containment of COVID19 is expected to start from June. Until then all of us must play our part in protecting everyone else. The combination of providence and human effort may save us from tremendous collective pain.
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