Frost Magazine asked our resident medical doyen Dr Kathleen Thompson to explain clearly and simply that though restrictions are starting to relax because the Covid rates have fallen, that is not the end of the story, and we STILL need to be careful, and mindful for ourselves and our communities. So over to Kathleen:
Many of us rather fancy ourselves as amateur Epidemiologists nowadays. After all, we know about R rates, virus variants, flattening the curve – just tell us the data and we’ll decide ourselves what to do – how hard can it be?
Actually although Epidemiology appears deceptively simple – it isn’t, there are many hidden complexities and potential pitfalls. This is why expert Epidemiologists always interpret data with supreme caution and sometimes make recommendations which armchair practitioners don’t really understand.
So as Covid rates have fallen, and restrictions start to relax, I want to explain Exponential Growth. A bit of maths I’m afraid, but I’ll try to keep it interesting.
When we think of increases, we tend to think of straight-line growth (first graph) – it’s what we learned in school and what we do see in everyday life.
However growth in nature is usually achieved by doubling, which if unchecked, creates a graph like the second one.
Bacteria (single cells which cause infection) are a good example. One bacteria splits into two; then each of these split again, making four, then there are eight and so on. Importantly it takes the same time for eight bacteria to double to sixteen as it does for one bacterial to split into two. For quite a while, it looks like there isn’t much happening in the second graph, but then very quickly the rate of increase takes off. If you look at the numbers on the vertical axes of the two graphs, it takes the same time for 1 to grow exponentially to over 524,000, as it takes for 1 to grow to just 20 with straight-line growth.
It’s not just bacteria that grow by doubling – cancer cells do too. People think cancer is fast-growing. Actually it doesn’t grow particularly fast, but cancer cells don’t stop growing. Normally, our bodies control our cells – once we reach adulthood, our bone cells are instructed to take a rest so that we don’t become giants. However if we break a bone, these bone cells are activated again, to produce just enough bone to repair the damage. Cancer cells ignore our body’s instructions and just keep growing, not fast, but continuously doubling. So, whereas a 0.5cm tumour won’t grow that quickly, by the time it reaches 5cm, it will then grow to 10cm in the time it took to grow from 0.5 to 1cm. This is why catching it early can make such a difference.
With Covid, it’s more about how many people are getting infected, and without interventions like social distancing, vaccination etcetera, this infection rate will also tend to double exponentially – so 100,000 infected people rise to 200,000 people as quickly as one infected individual rose to two.
Exponential Growth partly explains why, yes, it’s safe to cautiously expand our social interactions as per the Roadmap, but so long as Covid exists in the community, it’s by no means all over, and a sensible approach is essential if we are not to slip back. So please take care and stay safe.
By Dr K Thompson, award-winning author of From Both Ends of the Stethoscope: Getting through breast cancer – by a doctor who knows
http://www.amazon.co.uk/dp/B01A7DM42Q http://www.amazon.com/dp/B01A7DM42Q
Note: These articles express personal views. No warranty is made as to the accuracy or completeness of information given and you should always consult a doctor if you need medical advice.