If Indians can do just one thing to help the country reduce the overall number of novel coronavirus cases by up to 62 per cent, that one thing would be: SOCIAL DISTANCING.

The World Health Organisation has repeatedly stressed upon the importance of social distancing and experts after experts have appealed to people to strictly adopt it in their lives. In the medical fraternity, there are no two views that this - social distancing - is our best chance to reduce the spread of novel coronavirus, which has wreaked havoc the world over.

In the latest, a study by experts at the Indian Council of Medical Research (ICMR) has estimated that India may be able to reduce its Covid-19 cases by 62 per cent if social distancing and quarantines are strictly observed. The key to preventing the viral infection from spreading is imposing restrictions on the movement of people and keeping them from coming in contact with those who have contracted the disease or are showing its symptoms.

"Strictly implemented social distancing measures such as home quarantine of symptomatics (those showing symptoms) and suspected cases will reduce the overall expected number of Covid-19 cases by 62 per cent (in India), thus flattening the curve and providing more opportunities for interventions," the ICMR study says.

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The study was conducted weeks before Covid-19 turned into a global pandemic and has devised mathematical models to give an estimate of the difference early intervention can make in preventing the disease from spreading in India.

The study has predicted the trends of Covid-19 transmission for four Indian cities - Delhi, Mumbai, Bengaluru and Kolkata. These cities were chosen because they have a higher number of international arrivals than others.

So far, research on novel coronavirus has revealed that the reproducing number (Ro) -- the average number of people who are likely to be infected by an infected person -- for Covid-19 ranges between 1.5 and 4.9.

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Based on this, for their predictions, researchers in ICMR's study created two scenarios: optimistic scenario (when Ro is 1.5) and pessimistic scenario (when Ro is 4.9). These can be understood as the least risky and most risky scenarios.

Now, to understand the importance of social distancing measures to contain Covid-19 outbreak once the infection has already been detected in India, the researchers have given two predictions. First is the scenario when no intervention is taken and the second when intervention is taken.

'Optimistic' and 'Pessimistic' Scenarios

In the optimistic scenario (i.e. when Ro is 1.5) if an intervention is made, say if 50 per cent of those who are showing symptoms are put in quarantine (voluntarily or through screening and testing), within and average of three days of developing symptoms, the number of cases can reduce by 62 per cent, the study found.

This would help minimise the burden on public health services.

"As a consequence, the intervention has the effect of 'flattening' the epidemic curve, distributing cases over a longer duration than in the absence of intervention. The intervention could reduce the cumulative incidence by 62 per cent," the study notes.

The graph below shows that the impact that can be achieved if 50 per cent of symptomatic cases are quarantined within three days of exhibiting signs of the disease.

Source: Indian Journal of Medical Research

The study found that in the optimistic scenario, quarantining 50 per cent of symptomatic cases within three days of developing symptoms would reduce the cumulative incidence by 62 per cent.

However, under the pessimistic scenario, the projected impact in terms of reducing cases would be just 2 per cent.

The other projection that the ICMR study has made is how strict social distancing can delay the spread of Covid-19 in India, reduce the burden on public health infrastructure and so, provide more time to deal with the emergency.

The graph below shows that if timely interventions (strict social distancing) are made in the optimistic scenario, a city like Delhi could get between 400-600 days to prepare before the number of cases hit its peak. This additional time would give the healthcare system time to better respond to the cases.

Source: Indian Journal of Medical Research

But if no interventions are made in the optimistic scenario, the healthcare system would have just 200 days to respond to the outbreak and the number of cases would be very high.

Meanwhile, in the pessimistic scenario, healthcare system would have about 50 days to prepare itself.

Limitations:

While the mathematical modelling used in the study provides predictions for the spread of Covid-19 in India and the impact strict social distancing can have, it has certain limitations too.

The 62 per cent reduction in cases can be achieved in the optimistic situation when the reproducing number is 1.5. As this number increases, the percentage decrease in cases is likely to fall, as shown in the study itself (in case of pessimistic cases).

The mean duration of asymptomatic and symptomatic stages is very much uncertain. Some infections may be sub-clinical and never develop symptoms.

The study says there are some important uncertainties like natural history parameters, for example, the average duration of infection; the incubation period and the case fatality rate.

"Though we have tried to address some of these uncertainties through examining different scenarios for transmission, yet we caution that our model findings may also be sensitive to these other parameters. As more data become available about this new virus, subsequent modelling work can be refined accordingly," it said.

As for the selection of four cities, the study says the selection was made for simplicity and that the hypothetical scenarios were created only in four metropolitan areas that have the highest population density.

"These areas cover only about seven per cent of the total population of India. We ignored the rural population surrounded by these areas and their connectivity. Future work to address this gap will benefit from more systematic information on the rates of population flow between these different settings, data that were not available for our current study," it said.

Besides this, the prediction made in the study do not account the impact (if any) that seasons and changing temperature may have on Covid-19 because not much information is available about it.

"Although there appear to be differences in the immune responses of children compared to adults, for simplicity, this model has not accounted the disease prevalence with age structure," it added.

(The study was carried out by eight researchers from the Indian Council of Medical Research and Imperial College, London.)

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