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Why a Lockdown Helps Only When Judiciously Combined With Other Strategies

Why a Lockdown Helps Only When Judiciously Combined With Other Strategies

As of April 22, more than 2.6 million people around the world had been infected by the new coronavirus. India thus far has reported a total of 21,370 positive cases with 681 deaths, neither of which is a big figure for a country of 1.38 billion. However, the current trend in India – in light of the experience of other countries – raises some concerns.

The trend of infected cases in any country is a function of the number of people it has tested, and they must both be compared on a daily basis. In India, as we test more people every day, we also discover more cases (figure 1). And we have been finding that the virus’s spread hasn’t yet reached its peak.

That is precisely what happened in other countries during the initial phase of the spread: more testing revealed more infected people. It’s only when the number of new cases discovered each day declines even as the testing rate increases do we know that we have crossed the peak – as it happened in South Korea and New Zealand after 44 and 38 days, respectively (figure 1). India has not yet reached its peak.

Now, the testing rate – which is the number of tests a country is conducting to find one infected person (not to be confused with positivity rate) – for India is much lower than it is for South Korea and New Zealand (~23 versus ~46).

Table 1:

It’s important that public health officials aggressively track down the contacts of people who have tested positive for COVID-19, and quarantine them. Doing so can effectively reduce the number of new infections. Here’s how.

Say there are four groups of people: susceptible, infected but asymptomatic, infected and symptomatic, and recovered. (The ‘susceptible’ is the entire population minus those who have already been infected). Let’s assume that symptomatic people are immediately quarantined or hospitalised (depending on the severity of their symptoms). So only asymptomatic individuals are left able to infect the susceptible group.

Next, say a fraction of these asymptomatic individuals become symptomatic over time, while the remaining recover without any medical assistance and so slip under the contact-tracing radar. Most symptomatic individuals will recover after some time while a small fraction will die.

This process continues for many steps until individuals who have recovered can neither get re-infected nor infect others 1. As more people get infected, the number of susceptible people drops and the virus eventually dies out. The population in this phase is said to have acquired herd immunity.

Now, the actual number of people who have been infected is likely to be much higher than the number of infected people who have been identified (figure 2a). So it’s not a good idea for India to become complacent given the few cases it has detected thus far. Second, in the ‘no intervention’ scenario we just ran through, a large fraction of the population becomes infected before the curve flattens, which means more people die in a given population. This is the danger of promoting herd immunity.

Unlike India, Sweden took the herd immunity route to beat the virus and registered more than 1,900 deaths (implying a case fatality rate of 12%) by April 22. On the other hand South Korea, which has five-times as many people as Sweden but with a relatively similar age distribution, took the aggressive contact-tracing and testing route, and recorded only 238 deaths.

In the first scenario, we assumed the public health system didn’t intervene in any way and let the ‘simulation’ play out. Now let’s assume the same starting conditions and include one intervention: through contact tracing, public health officials identify a certain fraction of asymptomatic individuals every day and quarantine them as well. (Some of our simplistic assumptions might not hold in the real-world but modifying them won’t alter the basic nature of the outcomes either.)

In this scenario, even quarantining only a small percentage of asymptomatic individuals would appreciably slow the virus’s spread (figure 2b) and flatten the curve a lot more relative to the ‘no intervention’ scenario.

The number of active cases – i.e. all cases minus those who have recovered and those who have died – is an important number used to understand the stress on our healthcare facilities. In the ‘quarantine’ scenario, the curve climbs more slowly and is also flatter (figure 2c). So given India’s limited supply of testing kits and trained personnel, the government should prefer judicious testing through contact tracing over random testing, which has a much lower chance of finding infected persons.

If the government adopts physical distancing measures at the same time – even better. However, with a testing rate of around 23, India’s pace of tests is much lower than in countries that have been able to pull down the number of active cases, like Australia, South Korea, Germany and New Zealand.

Exiting the lockdown

Prime Minister Narendra Modi implemented a nationwide lockdown for 21 days on March 24, and extended it to 35 days on April 14 (so it is expected to conclude on May 3). This is a unique move but not in a good way. Lockdowns are useful to isolate infection hotspots and contain the virus there, thus minimising economic losses and maximising benefits for the larger population. However, India’s nationwide lockdown maximised economic loss, and simply debilitated the country’s large population of daily-wage earners and migrant labourers.

Areas that have been locked down don’t necessarily have a low prevalence of infections or fatalities. Wuhan, after being locked down for two and a half months, still hosted more than 60% of China’s total infected persons and 83% of total deaths (as of April 16). For every million people in Wuhan, over 4,500 got infected and 349 people died; if it had been a separate country, the city would have ranked an appalling third and fourth, respectively, among countries with at least 1,000 cases. Even regional containment depended heavily on research, contact-tracing, revamping care and mobilising medical personnel.

Lockdowns are also good to temporarily slow the overall prevalence of infection so hospitals don’t get clogged with too many patients and so the government can train more people for contact-tracing, prepare testing kits and improve infrastructure to accommodate patients. The availability of these resources will in turn place a new cap on the number of infected people who can be identified, isolated and treated.

This slew of measures isn’t only to improve Indians’ chances of surviving the new virus but also so our response doesn’t compromise our ability to treat patients who are suffering from other diseases. In 2017, India had 0.5 hospital beds per 1,000 people, of which some 20-30% might really be vacant. The support of India’s already stunted primary healthcare system will be crucial to expand contact-tracing, so primary healthcare centres should be allotted more resources so that India can exit the lockdown in an efficient manner.

India needs to learn an important lesson from other countries – that a lockdown helps only when judiciously combined with other strategies. Public health officials also need to listen to public-health reasoning, and above all to the people who have lost their livelihoods.

Sourindra Mohan Ghosh is a research consultant and Imrana Qadeer is a distinguished professor – both at the Council for Social Development.


  1. We have very little evidence to the contrary although we’re not 100% sure either.

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