R-Value and it's Covid Travails

SARS-Cov-2 aka Covid-19, the virus behind the current pandemic continues to be a nightmare for everybody - especially for statisticians. 

It was bad enough to have the Chinese obfuscating the truth about the original 'Wuhan virus' last year, but now we have a range of mutants (and double-mutants) that seem to be spreading in ways that are difficult to predict. This is is making the work of those who prepare statistical models much more difficult, and this in turn is affecting the quality of decisions being taken by policymakers.

Take for instance, the reproductive-value or R-Value for Covid-19. R is the number of people that one infected person will pass on a virus. 

The lowest possible R-Value is R-naught or R0. Also referred to as the Basic Reproduction Number, it is the R-value of a population that is assumed to have zero immunity against a new infection. R0 is the division of the number of new infections by the number of existing infections, or the average number of new infections over an infectious period (R0= new infections/existing infections).

Measles has an R number of 15 in populations without immunity. It means that, on average, every 10 people with Measles will infect 15 other people. For Covid-19, the latest R-value estimate for India, is around 1.30. This number is showing wide variations across states with Uttar Pradesh recording the highest infection value at 1.62, followed by Andhra Pradesh at 1.61.

The problem with the R-Value is that it gives us a picture of the past - by the time you calculate it, the number is already outdated. This is because it is based on data recorded on hospitalisations and death figures to get a sense of how many people have the virus – but the problem with this is that, since the virus’s incubation period is so long, it only gives an accurate picture of a few weeks ago.

Add to this the complications coming from recent mutations of the virus in different parts of the world, each with its own incubation period - the "UK" B.1.1.7; the "South Africa" B.1.351; "Brazil" P1, "India" variants B.1.36 (Bangalore) / B.1.1.7 (Punjab) and B.1.617 which contains two specific mutations - E484Q and L452R which is capable of 'immune escape', and infecting those who have already been vaccinated. 

Add to all this other newer emerging variants of concern (VoCs) and we have all ingredients for a statisticians' perfect nightmare. 

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LINKS & REFERENCES

* https://www.bbc.com/news/health-52473523

* https://theprint.in/health/indias-covid-r-value-increases-to-1-30-this-week-the-highest-since-april-2020/633783/

* https://www.weforum.org/agenda/2020/05/covid-19-what-is-the-r-number/

* https://www.statista.com/statistics/1101713/india-covid-19-cases-by-type/

* R0 Explained - https://indianexpress.com/article/explained/coronavirus-r0-reproduction-number-explained-6354339/

Watching Trees Grow

The world may have come to a standstill because of the Covid-19 virus but life goes on.

On 23 March 2020, a day after the "Janata Curfew" and a day before the nationwide "Total Lockdown" enforced by the government, I had gone to buy vegetables from the local Mother Dairy F&V Outlet. It was a bright beautiful day but the parks we already beginning to look eerily empty - there were no children playing on the swings, the usually raucous volleyball court was empty and so was the open-air gym.

Yet there was something beautiful about the silence, the rustle of fallen leaves underfoot, and the sharp calls of the ashy prinia's hiding in the bushes. As I cut across the park and walked towards the booth, I noticed something unusual.

An elderly couple stood under a pilkhan tree (Ficus virens)giving directions to a little boy perched in the barren branches. He was plucking and tossing down the bright pink shoots which were being diligently piled under the tree.

What was this for? 

The old man, a villager from Bihar, was not very forthcoming but his wife cheerily said that you could sauté these shoots turn them into a delicious dish.  Cooking shoots of the pilkan tree just like the bamboo shoots? I had never heard of such a thing before! 

Ten days later, when I went to replenish our stock of veggies the street looks so different. The pilkhan trees that had been bright green on one side of the road had all turned pink from the thousands of new shoots, while the one that one tree which had been the early bird in once sense had now turned completely green with a fresh set of leaves.

Clearly the little boy has plenty of new trees to climb and at least one family needs to buy fewer vegetables from the vendors during this lockdown.

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NOTES -

* It seem pilkhan leaves have long been a popular ingredient for the Thai curry phak lueat - https://en.wikipedia.org/wiki/Thai_curry