Daily wage labourers stand in a queue for free food at a construction site where activity has been halted due to the nationwide lockdown to slow the spreading of the coronavirus, in New Delhi, April 10, 2020. Photo: Reuters/Adnan Abidi.
Intuitively, it feels true that the earlier we impose a lockdown, the more effectively we can contain the coronavirus pandemic. However there is a strong possibility that a lockdown applied too early may yield only subpar results. To understand how, it’s important to know what a lockdown can and cannot do.
It is not the purpose of lockdowns to stop the epidemic by eliminating the virus. Viral epidemics stop only when the population acquires herd immunity: that is, when a sufficient percentage of the population becomes immune to the virus, and the virus can’t spread anymore. Herd immunity can be acquired either through vaccination or by becoming infected by the virus.
Since we have no vaccine, the epidemic will stop only when a sufficient number of us get infected (and subsequently recover). What percentage of the population needs to become infected in order to stop the epidemic depends on the virus’s infectivity. It’s generally of the order of 50-80%.
These days, many people get angry by the mere mention of the term ‘herd immunity’ because they see it as a lazy strategy that lets people contract the disease to build up the immunity in the population. But herd immunity is not a strategy: it’s simply a scientific fact that our strategies need to work around. A lockdown is one such workaround strategy. Lockdowns are not meant to bring down the proportion of immune individuals required to slow the epidemic. Instead, they can help keep too many people from being infected to the point of requiring hospitalisation at the same time, thus overwhelming our hospitals.
We need to be clear about the lockdown’s objectives. Imposing a lockdown in the hope that it will somehow eliminate the epidemic is futile. Many of us have been led to believe that if we effectively implement a lockdown, we will reduce the number of people infected. It’s true that the lockdown can limit the number of infected people at a particular point in time — but ultimately, the total number of people who will be infected is the same with and without lockdown. The lockdown is a way to ensure this total is spread over a longer period.
In short, a well-designed lockdown can flatten the curve. And the more we flatten the curve, the longer the virus takes to infect all the people it can infect. So under a lockdown, the epidemic will go on for longer but at lower intensity, instead of happening over a short period of time in a burst.
The fact that a large number of people will ultimately be infected by the virus is not as terrible as it sounds. Most of us who get infected may not even realise that we are infected, and the symptoms that most people get are not more troublesome than those due to the ordinary flu. Only a small percentage of the population will get seriously sick and die (although in absolute terms this fraction translates to a large number in the Indian population). Even in Italy, the death toll of 19,468 on April 11 was less than .03% of the country’s total population.
Flattening the curve allows maximum possible hospital care to be given to those who get seriously sick. By curtailing the movement and interactions of and among people, lockdowns temporarily slow the infection’s dispersal through the population. When the lockdown is lifted, the infections will start again, though at a slower rate than before. In effect, the requisite herd immunity is acquired in two smaller chunks instead of in one steep spike.
Lockdown schedule has to be supported by data
Now, the curve can be flattened only if we schedule the lockdown properly with realistic data specific to India. Simply applying it as soon as possible does not guarantee positive outcomes, much less when driven by the conviction that lockdowns can stop epidemics in their tracks. In fact, some epidemiological models indicate that if a lockdown is applied too early, it may not be able to flatten the curve at all, and may postpone the peak into the future.
Specifically, a lockdown can be considered to be too early if it kicks in long before the epidemic’s peak. The more populated a country, the longer it will take to reach its peak. Now, it’s important to remember that ultimately, it is not the health system but the human body that fights the virus. So an early lockdown effectively means a less-than-healthy population will be facing the epidemic when the virus resurges at the end of the lockdown; our bodies will have been weakened both physically and mentally due to the concomitant economic and social downturn.
Scientific analysis of reliable data is essential to understand how the epidemic is playing out within the country. Without reliable data, it is impossible to determine what the epidemic trajectory for India is like and where we are on the trajectory at any given point.
Indeed, there is a strong chance India is experiencing a milder epidemic than are countries in the West. This is not wishful thinking: a lot of countries around us, like Pakistan, Singapore, Thailand, Malaysia and the Philippines, seemingly have flat growth curves, at least at present; most of Africa does not seem to have even entered the epidemic stage. Scientists are trying to understand why in different ways but the absence of an explanation shouldn’t consign this possibility to the dumps. This said, India has tested very little, so what data we have available does not suffice to satisfy ourselves that we are indeed having a mild epidemic.
Computer simulations show that imposing a short lockdown closer to the peak could be more effective than an early lockdown of any duration. Locking down early implies that we divide the total number of possible infections into a tiny first chunk and a much larger second chunk.
We must quickly collect reliable data. It is not enough to find out how many people are getting sick and how many are dying. We need to know, for example, what percentage of our population has infections with no symptoms or symptoms so mild that they don’t get reported. This can only be done by randomly testing the population with antibody-based testing kits, and using those test results to then estimate how close we as a country are to achieving herd immunity.
We must also consider whether we can achieve better results by strictly isolating the vulnerable population and practising physical-distancing instead of halting all economic activity. We must choose our strategies based on scientific knowledge and reliable data specific to India. Hopefully we will acquire the data we need soon, and from that perhaps glean the possibilities of even milder responses instead of persisting with a blanket lockdown with staggering economic and human costs.
Roschen Sasikumar is a retired scientist from CSIR-NIIST, Trivandrum.