June 21, 2021

COVID-19 Containment Strategies in Mumbai



The Brihanmumbai Municipal Corporation (BMC) started releasing a detailed daily PDF containing information on a variety of indicators such as mortality, containment zones, bed capacity, vaccinations, etc. from June 2020. Such data is extremely useful not only for formulating short-term policies but also for assisting longer-term academic research. A long-standing issue with using the data, however, has been that the authorities replace the PDF each day with fresh information and remove the prior day's document. This practice has limited any kind of temporal analysis till now. 


At IDFC Institute, we have been able to gather all such PDFs from June 2020 until the present. We are in the process of converting all relevant indicators to a machine-readable output and will put them out as a public-facing database in due course. In the meantime, we will put out a brief analysis of them along with the related datasets.


In our first two posts, we discussed COVID-19 mortality data for Mumbai (read here) and tests data (read here). We have now mapped and analysed the trend in COVID-19 cases and containment zones, at ward level, and looked at the following indicators

  1. Cumulative new cases

  2. Number of Slum/ Chawl Containment Zones

  3. Number of Sealed Buildings

  4. Number of Sealed Floors


Learnings from the data


BMC collects most of its data on a daily basis which has led to updation and adjustment of such data over time. As a result, there are a number of discrepancies in the dataset. For instance, cumulative positive cases should increase incrementally on a daily basis. However, on some days a lower cumulative value was observed compared to the previous day. Since, the number of fresh cases recorded on any given day cannot be negative, such a discrepancy is likely to be a result of adjustments to the data. Hence, we have aggregated change in new cases to a weekly level to minimise such data gaps. 




Containment strategies are a form of urban governance, analysing their use across different regions within the city can highlight disparities in governance mechanisms but help proactively address gaps in service delivery. Combining this with ward wise positive cases can have direct implication on the deployment of vaccinations across the city and other proactive mechanisms for disaster preparedness.


In this blog we use the dataset to investigate a shift in positive cases and containment strategies between the first and second wave in Mumbai.  We have made initial observations on how strategies were deployed on a ward level and analysed potential reasons for the changes. This is with the intent of initiating conversations on the subject and developing new research questions. 


City-wide containment zones


Since the beginning of the pandemic, the BMC has implemented two distinct containment strategies to limit virus transmission. The first is the slum and chawl containment zone strategy, where the containment zone was defined in March 2020 as an area of 3km radius from the epicenter (the household with the positive case). As cases increased in the city, the size of such containment zones was reduced to a 100 meter radius in May 2020. Today it only includes the immediate households surrounding the infected household in a slum or chawl. 


The other strategy is to enforce micro containment zones. This involved the sealing of an entire building if there were five or more cases. It was put into effect for low-rise and high-rise buildings across the city. If a building had more than five cases, it was classified as  a containment zone. Cities such as Bengaluru and Lucknow, in contrast, have used a sealed floors strategy since the early weeks of the pandemic. Mumbai also adopted this strategy, towards the end of 2020. This ‘super micro containment zone strategy’ only places restrictions on immediate neighbours living on the same floor. 


In each case, the restrictions within a containment zone are similar to the ones placed on citizens during the nationwide lockdown: no interactions allowed between households and sealed entry and exit points. 


The data shows that the number of slum and chawl containment zones and sealed buildings in Mumbai declined sharply at the start of 2021. During the second wave, Mumbai’s daily COVID-19 cases peaked at 11,200 on 3 April 2021. This was almost four times the highest daily cases of 2,484 cases reported last year, in October. Despite this spike, the number of containment zones and sealed buildings were down by 88% and 93% respectively during the peak of the second wave, compared to the first in early October 2020. This suggests that the dependence on the containment strategies significantly decreased between the first and the second wave.


There could be various reasons behind such a trend: 


  1. The strategy shifted to sealing floors rather than buildings 

  2. Recent reports suggest that there was less virus circulation in slums compared to high-rises and formal apartment complexes. According to an article by Mint, about 90% of the cases in Mumbai in April 2021 were observed in high rises. 

  3. Ground level efforts to improve health access and infrastructure, either by civil society or the government, have helped improve service delivery and prevention mechanisms.  This has reduced the dependence on containment strategies. 


Analysis of the weekly new cases


We’ve analyzed the trends of new cases in six wards of Mumbai. These six wards were picked as they reported the lowest or highest incidence per 100,000 population. These wards are located in the North Eastern Suburbs (Mulund), North Western Suburbs (Borivali), Western Suburbs (Andheri East and West) and Southern Mumbai (Colaba and Grant Road). Andheri East, Andheri West and Borivali had the highest number of cases during both the first and the second waves in Mumbai. Borivali saw the biggest increase in new cases during the first wave, on 3 Oct 2020. During the second wave, the cases in Borivali tripled. But it was Andheri West that saw the biggest jump in cases during the second wave which was almost five times as much as the first wave on 4 Apr 2021. 


In the other three wards, Colaba, Grant Road and Mulund, the absolute number of cases were lower in the first wave. While the cases approximately tripled in Grant Road and Mulund during the second wave, they were still lower than the other wards. 


Out of these six wards, the incidence (positive cases per 100,000 population) was much higher in the wards that otherwise registered a low number of cases. The number of persons affected in Colaba, Grant Road and Mulund had approximately tripled compared to the first wave. During both the peaks of COVID-19 waves, Grant road showed the highest incidence, although the absolute number of cases was lower than the other wards across the city. On 4 Apr 2021,  909 people per 100,000 were infected in Grant Road compared to 266 people per 100,000 during the first wave.  


Borivali, Andheri East and West saw the biggest jump in cases in the first and the second wave but recorded the least number of people affected per 100,000 population. 


Comparison of Containment Strategies Across Wards


To understand how the strategies were deployed at  a ward level, we compared wards from different regions within Mumbai. We looked at wards with similar population densities and regions but with diametric slum populations.


Andheri East is a ward with Majority slum population, it  has more containment zones than Andheri West throughout 2020. The ward also had a higher number of sealed buildings in July and August 2020. However, this seemed to switch in the second wave with Andheri West having five times the number of sealed buildings than Andheri East. The containment strategies in Andheri east were more in use. 


A similar pattern can be seen in the south Mumbai wards of Dadar and Byculla. Throughout 2020, Dadar had significantly more sealed buildings than Byculla on most occasions. By early April 2021, however, Byculla had 10 times as many sealed buildings as Dadar. Again, a ward with a majority non-slum population showed a greater usage of containment strategies during the second wave. 


Finally, we analysed a set of wards with the lowest population densities in the peripheries of the city. Mulund is a rapidly modernizing ward with a growing presence of high rise buildings and large gated colonies. Despite that, the ward had more than 30 active slum and chawl containment zones on each day between July and November 2020. Considering its low slum population, this could indicate that the ward had a greater presence of chawls. Second, Mulund had significantly more sealed buildings than Bhandup between September and October 2020 however March 2021 onwards Bhandup had more sealed buildings while Mulund had none. This could imply that the sealed floors strategy was actively used in a ward like Mulund, negating the need for a sealed building strategy. 



Policy Implications & Way Forward


To build on this preliminary analysis, researchers can explore how the containment strategies have been implemented across wards and how they compare with the number of cases in the wards. A deep dive can help identify regions within the city where the strategies have either been overutilized or underutilized. It will also highlight factors such as better access to health infrastructure in specific wards as reasons for reducing the use of containment strategies. 


Secondly, understanding the degree to which slums were affected by the first and second wave of COVID-19 is also possible by combining such data with other data such as the  upcoming seroprevalence surveys. This will help bring out contrasts in slums that are faring better than others and this will be crucial to standardize best practices. Currently the Dharavi model which was coined before the first wave, is the benchmark for crisis management in slums. While this model is expanding to other slum communities, the ground level practices need to be standardized in order to see the same kind of success. 


Lastly, understanding positive cases and containment strategies on a ward level can influence the distribution and management of vaccination drives in the city. If slum communities are showing a lower prevalence of the antibodies and lower case counts it would mean that they are less immune to the virus in the coming wave. This would mean that vaccination camps in such settlements need to be set up on priority in the coming weeks

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