‘We should see much lower numbers by end of the month’

What is the latest observation for Mumbai?

I think the peak in Covid-19 numbers was reached around the 20,900-mark on January 7-8. The number of people testing positive has been coming down since then. Usually, Monday and Tuesdays are lower-biased numbers for Mumbai as, sometimes, weekend testing is low and it takes time for the numbers to be collated from the hospitals. For the same reason, Wednesday numbers are upper-biased.

In Mumbai particularly, a person infected in a slum is much less likely to get tested compared to a person infected in a high-rise. After a while, the virus does run out of people to infect and we are seeing that in Mumbai, where the reported cases are coming down as expected. We should see much lower numbers by the end of the month.

What is different about the infections this time as compared to the second wave?

What is different this time is that the growth of the virus is more synchronised. With Delta variant, it started with Maharashtra and took off in Mumbai but then it took some time to reach other metros and rural areas. But this time around, you are dealing with a variant that is more infectious than Delta and is able to better break through the immunity provided by prior infections and vaccines.

Thus, our health care infrastructure needs to be more robust as infections are rising across the country in more or less the same time. It may not show in the data, as very few get tested. In Mumbai, we estimate that 3-4 times more people will get infected by Omicron compared to Delta.

Although, since more people have already been infected and vaccinated, and Omicron is milder, an average infected person, as per our estimate, has about 20 per cent chance of being hospitalised compared to the second wave, and about 10 per cent chance of dying compared to the earlier Delta wave.

Is another peak in the number of cases in Mumbai expected?

I do not expect another peak to happen in Mumbai anytime soon. There were indeed certain restrictions put in the city starting December 30 and one can see from the Google mobility report that it did have an impact as the movement was reduced. What that means is when we open up again, we may see a slight increase in the cases but I don’t expect the rise to at all match up to the peak numbers we saw on January 7 and 8 with Omicron at least.

Is it also possible to predict the number of cases along with the time of peak?

The number of cases is always hard to predict because they are a function of testing strategy, mix of people getting infected (slums, non-slums, high-rises etc). But in the model that I along with research associate Daksh Mittal worked on, we could predict when the number of people infected will peak.
Our model is quite intricate and we individually model all the 13 million people in the city. We feed it with the conditions that existed in late November in the city— more than 80 per cent already infected, single and double vaccinated citizens as per data— then we inject the number of Omicron infections that existed in the city in early December.

We also have information from South Africa and the UK available to us viz what percentage of the population will be amenable to re-infection, what kind of transmission rate to expect. With all these information in the model we can get a rough idea of when the number of infections will peak.

Since a fraction of infections will result in reported cases in a few days, we get a fair idea of when the peak will occur. We can also estimate resultant hospitalisations and fatalities.

Since the mathematical model’s effectiveness is dependent on the data that is fed into it, how good is the quality of data available from the Mumbai Civic body?

I think the city administration did a wonderful job of preparing a Covid-19 dashboard and they should be congratulated for it. We would have liked to know amongst the reported cases, the number of re-infections, the number of doubly vaccinated citizens, and the timing of their vaccination. This information is recorded and if it were made available, that will help make the model more accurate.