New Delhi:

Mathematical models of the progression of COVID-19 show it would be “possible” for Delhi to have 5.5 lakh cases by the end of July, several scientists have said while stating that community transmission of the disease may have started a while ago.


Warning of more trouble ahead, Delhi Deputy Chief Minister Manish Sisodia on Tuesday said the number of COVID-19 cases could surge to 5.5 lakh by July 31. This is dramatically higher from the city''s tally of 31,309 cases on Wednesday. India’s COVID-19 count is 2,76,583.


“The model that I used for India found that there could be around 8-10 lakh cases in India by mid or end of July. So it won’t be surprising to get to those figures (5.5 lakh) in Delhi,” said Samit Bhattacharya, mathematics professor and researcher at the School of Natural Sciences at Shiv Nadar University.


“Delhi getting around 5.5 lakh cases by end July might be possible as the number of cases is growing,” Bhattacharya told PTI.  


According to virologist Upasana Ray, only epidemiologists and statisticians can comment on exact numbers and predictions.


"I believe that if the government is telling something, there must be some basis to it,” Ray, senior scientist at CSIR-IICB, Kolkata, added.  


Reaching the alarmingly high figure of 5.5 lakh is possible using mathematical modelling, agreed Lovi Raj Gupta, executive dean of Science and Technology, Lovely Professional University (LPU) in Punjab.


"The validity and the accuracy would depend on the selection of the model based on the variation of data. As this is time-series data, trends and seasonality play vital role,"  Gupta told PTI.


Time series analysis is a statistical technique dealing with data in a series of particular time periods or intervals.


"You look at what is happening previously and average it out and on the basis of that you can create the differencing pattern of the future. It can be very well done using time series variation,” Gupta said.


Mathematical modelling can be used to understand how a virus spreads within a population, according to a research article published in the journal BMC Public Health.


The essence of mathematical modelling lies in writing down a set of mathematical equations that mimic reality. These are then solved for certain values of the parameters within the equations.


The solutions of the mathematical model can be refined when information already known about the virus spread is used — for example, available data on reported number of infections, the reported number of hospitalisations or the confirmed number of deaths due to the infection.


Talking to reporters after a meeting of the Delhi Disaster Management Authority, Sisodia also quoted officials from the Centre as saying there is no community transmission of COVID-19 in Delhi.


Delhi Health Minister Satyendar Jain added in a separate conversation with the media that the source of infection is "not known" in nearly half the fresh cases being reported.


Bhattacharya said community transmission “definitely” started a long time back in Delhi.


“It doesn’t mean the whole of Delhi will have infections uniformly for community transmission to happen. Nearly 30,000 infections in Delhi have already happened and according to the Delhi population it is definitely community transmission,” he said.


“As far as my understanding of disease transmission, in local transmission there is a small spike in the number of infections. After that it gradually increases, and definitely at that point starts the community transmission.” Bhattacharya added.


Ray explained that community transmission is said to happen or is a stage of disease transmission which by definition lacks exact source of transmission for many reported cases, that is the source of infection might not be traced back.


“We have seen a very long and stringent lockdown in our country. Yet, the number of cases have been seen to be rising. In many cases we can''t trace back the source.


"If the rise in COVID 19 cases can''t be linked to community transmission, then the next question should be…..what is the reason for such an increase? Is the virus more virulent? We don''t know that either. Are we bringing in infection from elsewhere? How can that be? It was a lockdown.”


While all these assumptions are true, it will not be wrong to say that just an increase in infection numbers won''t point to community transmission, Ray added. 


COVID-19 pandemic may be over in India around mid-September, say health ministry officials

When will the coronavirus pandemic end in India? There is no definite answer yet, but senior officials of the Health Ministry predict that the pandemic in India may go in mid-September this year.


According to Dr Anil Kumar, Deputy Director General (Public Health), Directorate General of Health Services of the Ministry of Health and Family welfare, the pandemic in India will be over in mid-September.

In his article published in Epidemiology International Journal, Kumar, along with co-author and Deputy Assistant Director General (Leprosy) of Directorate General of Health Services, Health Ministry, Rupali Roy, have predicted that the pandemic would extinguish in India in mid-September.
Their prediction is based on Bailey`s model where Relative Removal Rate (BMRRR) is considered for reaching a conclusion.


Speaking to IANS, Dr Kumar said, "There is a well-known model called Bailey`s Model. It is based on Relative Removal Rate which means how many cases are entering the pool and how many are going out of the pool. When the number of infected is equal to the number of removed patients, the coefficient will reach 100% threshold, then this pandemic will be over."


In this model, the removal rate is calculated which is the percentage of removed persons in the infected population. Further, a regression analysis has been done to show the linear relationship between the total infection rate and the total recovery rate."This model is applicable on any infectious disease. Whatever you do, you will be reaching 100 percent one day. The relative removal rate means all those who have got infection will be either cured or dead. when we did the study on May 19, it was 42% but now it is around 50 per cent and in the middle of september, it will be 100 percent," said Kumar.


According to this mathematical calculation, taking the rate to higher and higher level is reflection of moving forward in the right direction and success of control measures being taken. The linear regression analysis has been used in this study and it is showing that the linear line is reaching 100 in the middle of September 2020.


"So it may be interpreted that at that point of time, the number of the infected will be equal to the number of removed patients, and that`s why the coefficient will reach 100% threshold," said the study.