A woman wearing a protective face mask buys fruit in a market, amidst the spread of the coronavirus disease (Covid-19) in Mumbai,. (Reuters Photo)
A woman wearing a protective face mask buys fruit in a market, amidst the spread of the coronavirus disease (Covid-19) in Mumbai,. (Reuters Photo)

Crucial lessons to be learnt from Covid-19 outbreak

The spread of Covid-19 holds crucial clues about virus behaviour and how it can be controlled. This is important at a time when the first signs of the second wave are apparent in some states
UPDATED ON MAR 01, 2021 12:46 PM IST

In a year since the start of the Covid-19 outbreak in India, more than 11 million people have been infected and more than 160,000 have lost their lives. And while India has managed to control its first wave (and so far, only major wave) of infections, how the pandemic unfolded through the year has left behind troves of data on the virus spread in both statistical as well as epidemiological terms.

Through the past year, government-assigned as well as independent data scientists across the country embarked on a massive tracking exercise that studied the spread of the virus in the country. Not only has this data given a clear in-depth view of how the virus covered the entire country in a matter of months, but it also showed how the first wave of the outbreak eventually receded.

Within that data also lie crucial lessons to be learnt (especially given how cases are again inching up in the past few weeks). It can reveal what signs emerge at the start of a Covid wave so governments and people can brace for a fresh spike.

How the pandemic unfolded

While the first batch of cases was reported in India on March 2, the first month or so of the spread of the disease in the country mostly consisted of infections being reported in people who travelled abroad, or their families, friends, colleagues and neighbours. The cases were mostly confined to metros that saw a large influx of international travellers, with Delhi, Mumbai and Chennai becoming the early areas of concentration of infections.

Since much of the first month of the outbreak, March 2020 -- there were a couple of isolated cases in Kerala in January, but the Covid outbreak in India really began in March -- had no restrictions on movement of people, infections slowly stopped being confined to isolated clusters within cities (like buildings or localities), and a slow but steady trickle of cases started emerging across several states. The national lockdown kicked in only on March 25.

Fuelled by cases from the three metros mentioned above, Maharashtra, Delhi and Tamil Nadu started emerging as India’s first hot-spot states by the start of April. In the first week for April, nearly half of all cases across India were coming from just these three regions – Maharashtra was responsible for 19% of all new infections, Tamil Nadu 15%, and Delhi 12%.

These three regions remained the biggest contributors to the national tally through the next two months – May and June. No other state came close to reporting the kind of infection numbers these three were exhibiting at the time. It wasn’t until late July that the outbreak started swelling uncontrollably in other regions of the country. The first state other than the “Big Three” was Andhra Pradesh. This again followed a trajectory much like the ones before it – one or two hot spot regions emerge first, which later lead to a steady stream of infections to other regions. Karnataka (with Bengaluru becoming a hot spot) followed quickly on its heels.

It wasn’t until early August that cases swelled in “other” regions. An important point worth noting is that the “other” category in the chart refers to a grouping of 30 states or Union Territories, which really puts into perspective just how big the numbers were from the states that saw the outbreak first— Maharashtra, Tamil Nadu, Delhi, and later Andhra Pradesh and Karnataka.

The regions affected first carried India’s tally in the initial months of the outbreak; “other” states started swelling after August, when the country saw cases that were truly spread across the nation—breaking away from the hot spot-centered spread.

This phenomenon is not limited to just India, and is very crucial to understanding how this virus spreads across the world. The trend of a handful of hot spot regions emerging first, then a heavy and steady stream of cases from medium-population regions, was identical in nearly every major country that has seen outbreaks.

A look at the rise and fall of India's first coronavirus disease (Covid-19) wave
A look at the rise and fall of India's first coronavirus disease (Covid-19) wave

In the US, New York City (and later NY state) along with California were the first hotbeds of the virus, before it ripped through the Midwest and South. The same trend was visible in Brazil, where the virus first clustered around São Paulo and Rio de Janeiro before it ravaged the rural parts of the country. In the UK, London and was the first outbreak centre before cases emerged throughout the country.

On the other end, when cases started receding, this phenomenon worked entirely in reverse. The drop in cases was generally fuelled by hot spot regions first, and then the “other” regions brought their outbreak in control. When the Indian wave peaked mid-September, seven regions – Maharashtra, Tamil Nadu, Delhi, Andhra Pradesh, Karnataka, Uttar Pradesh and Kerala – were responsible for 64% of all infections in the country, while the 30 “other” state/UTs were only responsible for 36%. The fall in overall numbers started with the former group seeing a massive drop in infections. On the week India’s wave peaked (September 16, 2020) Maharashtra’s share in the country’s infection was 24%. In the next two months, the state’s contribution to new infections across the country dropped to 9%. Similarly, Tamil Nadu’s share went from 20% in early August to 5% by the end of November. On the other end, the “other” states were responsible for 36% of India’s infections on September 16, and their share rose to 47% by November-end.

Learning from the trend

The reason this “hot spot first, then wider spread” trend is crucial is because it can serve as a harbinger for second waves, or warn of wider trends of resurgence. While a lot of has been written about the recent increase in cases in a handful of states (led by Maharashtra) what is alarming is that the trend is following nearly the same pattern as before.

Cases swelled in Maharashtra first, which was followed by Punjab, Madhya Pradesh and Madhya Pradesh, while Kerala remained a hot spot from the first wave. Now cases are again rising in cities like Delhi -- around 250 a day over the past three days from as low as 130 on the three corresponding days a week ago.

At a time when travel restrictions across the country are at the lowest levels since the start of the outbreak, it would not be surprising if the first wave’s “hot spot first, then wider spread” trend starts to resurface. Currently, the country is at the first phase of this trend with a handful of hot spots regions emerging. Unless some drastic measures are taken to control the spread of the virus in these regions immediately, the second phase of this trend that would see a massive increase in cases across the country soon.

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