When BMC's first sero survey was conducted in July, it revealed that 57% of those surveyed from slums and 16% of those living in buildings were exposed to the 2019-nCoV. The corresponding numbers in the second survey in August were 45% and 18%, although they may have been less due to the decline in the antibodies tested.
Researchers at Tata Institute of Fundamental Research (TIFR), BMC's sero survey partner, incorporated the findings of these surveys into their mathematical model to plot Covid-19 trends in Mumbai. "Based on our model, Mumbai, at present, has a high positivity rate of 80% in slums and around 50% in residential areas," said Dr Sandeep Juneja, dean of school of technology and computer science, TIFR. Here, he provides a scientific basis for further unlocking in Mumbai:
Q: The authorities will decide in January on whether all passengers can travel by trains. Is it safe to completely reopen Mumbai's lifeline?
A: The state administration has done a great job of gradually opening up trains in Mumbai. One hears of some overcrowding in trains, but, fortunately, this has not resulted in a major increase in the Covid-19 numbers. The high positivity in the city, combined with declining cases, hospitalisations and fatalities, suggest this process of gradual opening should continue, but with more boldness. Mumbai has substantial hospital beds, ICUs and ventilators to handle cases that may occur due to further opening. The city has suffered enormously from travel restrictions, and it's important to open up further if it can be done safely.
Q: Travellers from other cities have complained about the restrictions imposed on travel to Mumbai. How long should we continue with these restrictions?
A: While extensive testing of travellers into the city is important to control the disease, this needs to be balanced with the hardship it causes to travellers and to the economy. In the last two weeks, only a couple of hundred domestic travellers to Mumbai through trains and airplanes tested positive.
As per our model, 8,000-10,000 people get infected in Mumbai each day around mid-December (this number is higher than the daily reported cases as only a fraction of those infected get tested). Thus, the strategy of extensive testing is not particularly effective and needs to be adjusted to cause less hardship.
Similarly, careful data analysis is needed to check if less stringent measures could work for international travellers to India.
Q: Should schools and colleges reopen in January?
A: Our model suggests opening schools and colleges in January or later would lead to a small, but not insignificant, increase in the number of infections in the city: around 500 to 1,500 people daily for a few months before the infection stabilises.
Contrast this with the peak of the infection in May, when estimated 60,000 residents were infected daily. Considering the majority of the population in high-density areas (around slums) is already infected, and the population there is typically younger than the rest of the city, the risk from opening schools in those areas is less, and they may be safer to open.
Much of the other, less dense parts of the city could continue with online education for a few more months until the elderly are vaccinated.
However, classes for senior students could be started and should largely be held outdoors to reduce transmission risk.
Some recent research suggests children tend to transmit less than adults. This aspect has not been incorporated in our model, and may suggest that schools are safer than suggested by our model output.
Q: What about the risk of a second wave from the year-end holidays?
A: If the population interactions during Christmas and New Year celebrations are of the same order as for Dussehra and Diwali, then the resulting increase in infections is likely to be lower this time around.
Q: When the Covid vaccines do arrive, they will have to be disbursed in a phased manner. Who should be in the priority list?
A: The government's plan of first vaccinating the healthcare workers, police, transportation and other workers, those above 50 years of age and younger population with comorbidities is a sound one.
My suggestion is that within this list further prioritise those above 60 years of age. They have the highest mortality and are less likely to have been infected in the past. So per vaccine, lives saved would be the highest. Our analysis suggests around 10% of Mumbai's population is above 60. If they are vaccinated with a perfect vaccine with 100% effectiveness, let's say on February 1, the city will witness 55% to 65% reduction in fatalities over the next six months compared to the no-vaccination scenario.