Mumbai: Covid-19 fatalities may peak by the first week of May, say scientists

ByPriyanka Sahoo, Mumbai
Apr 15, 2021 01:01 AM IST

The second wave of Covid-19 cases in Mumbai may be at its peak now and fatalities are likely to peak by the first week of May, according to modelling and data analysis by two separate groups of scientists

The second wave of Covid-19 cases in Mumbai may be at its peak now and fatalities are likely to peak by the first week of May, according to modelling and data analysis by two separate groups of scientists.

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HT Image

While projection of peak in the number of daily cases is difficult, simulation models can project a likely peak in the number of fatalities in the future. A simulation model, developed last year by scientists from the Tata Institute of Fundamental Research (TIFR), Mumbai, and the Indian Institute of Science, Bengaluru, estimates that Covid-19-related fatalities will peak in Mumbai by the first week of May. Similar projections have been made by Murad Banaji, senior lecturer in Mathematics, department of Design Engineering and Maths at the Middlesex University, London, who has been studying the epidemic in Mumbai.

The TIFR model mimics a city with a population of 13 billion. It takes into consideration different population demographics, densities, household sizes and interaction of people with each other. Initial parameters were chosen such that the death rates matched the actual observations in April last year. The simulations that arose from the parameters chosen were done for various scenarios such as compliance to rules, treatment and vaccination.

Projections by the TIFR model made last October almost matched up to the actual observations on ground till January and then after adjusting for laxness in population behaviour around the new year, till around March this year.

“Our model suggests that the peak fatalities in Mumbai may occur by May first week. Since cases generally lead the fatalities by around three weeks, this suggests that the cases should be peaking around now,” said coordinator of the simulation project at TIFR Sandeep Juneja, who is the dean of the institute’s school of technology and computer science.

Banaji said that there were hopeful signs that cases are peaking at the moment. “Predicting a peak in the number of cases is difficult– with or without modelling—because we never know how effective mitigation will prove to be. But there are hopeful signs that cases are peaking at the moment. The weekly average of new cases and test positivity have both fallen in the last few days. Hopefully, this is a trend that will continue. It is correct that deaths are lagging behind cases by around two to three weeks. So, presuming that cases are peaking now, we should see daily deaths falling by early May, or even a little earlier,” said Banaji.

Dr Rahul Pandit, a member of the state-appointed task force to mitigate Covid-19, said, “It can be said that cases in Mumbai are peaking right now. However, in Mumbai, last year we saw that the numbers remained high for some time and we are expecting a similar trend this year. So, cases will continue to remain high for the next couple of weeks before starting to drop.”

Analysis by both groups also suggests that more infectious variants of Covid-19 are at play now. “The surge that we saw in the cases around mid-March or so was unexpected, suggesting that more infectious variants may be at play. This is likely to result in much higher fatalities than our model was projecting. However, we do expect the peak in fatalities to be reached by early May. This fact appears robust to various reasonable scenarios that we modelled,” said Juneja.

Banaji said that there was a growing and immediate need for genome sequencing to understand the pattern of the spread of the virus. “It is hard to explain the speed and size of the surge without more transmissible variants and/or “immune escape” variants. These are variants against which a high level of prior infection in the city does not provide strong protection. Regular genome sequencing is urgently needed to help make sense of these patterns in Mumbai and more widely,” said Banaji.

Dr Lancelot Pinto, a city-based pulmonary specialist, said that the current variants of the virus appear to be more transmissible. “On the ground, in our experience, it does appear that the variant at play now is more infectious. We are also seeing a rise in the close contact transmission rate,” said Pinto.

The close contact transmission rate is a measure of how many people a patient can contaminate upon close contact. “While last year we would see one person in a family of five testing positive, now we are seeing four to five times what we did last year,” said Pinto.

In a silver lining, the TIFR analysis also shows that despite the high chance of existence of new variants, the shifted case fatality rate is lower than it was in September when Mumbai saw its last peak.

Case fatality rate or CFR is a measure of severity of the disease that helps policymakers and experts plan treatment strategies. The shifted case fatality rate (SCFR) is an improved measure of the CFR. CFR is the ratio of the fatalities observed to the reported cases observed. Therefore, a 2% CFR can mean a 2% chance that a person, whose infection has been detected, will not survive the infection.

There is, however, an important caveat: “Even if the CFR is low, say 1%, it is still very concerning because the number of cases are very high. So compared to last year, a 1% CFR can mean almost 500 people dying a day, if there are 50,000 positive cases,” Pandit pointed out.

Typically, a reported case, if it results in a fatality, does so about two to three weeks later. When cases are rising, the CFR does not account for the fatalities that occur in future and underestimates the fatality rate. To correct this, the SCFR is the ratio of observed fatalities to the cases that occurred around 18-20 days earlier.

Currently, the SCFR of Mumbai and Pune is between 0.8 to 1%, lower than 2.5% in Mumbai last year. “A high CFR implies that more people are dying per reported case, but it may also mean that there is insufficient testing so many infections are not tested and are missed out. SCFR is lower now compared to September last year. This is very likely because a person with symptoms is more likely to get tested now compared to September. It may also be lower because we are better in treating people with Covid-19 now,” said Juneja.

However, Pinto said that even if the SCFR was low, rising cases would put undue pressure on the existing healthcare infrastructure of the city.

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