The link between coronavirus cases and hospitalisations is weakening thanks to vaccination—but coronavirus cases are growing exponentially in the UK. I wanted to find out how these two opposing forces might interact, so I added some (tentative) projections to yesterday’s graph. (If you missed it, it’s probably good to start by taking a look at it to explain how this type of graph works.)
The result seems to be: exponential growth crushes the linear-ish weakening of the link between cases and hospitalisations.
What I did:
- Updated the graph with the latest data (as available from the UK Government coronavirus dashboard on the evening of June 30th 2021.)
- Fitted an exponential to case data (the orange line extends back a bit so you can see it’s reasonable).
- Fitted a straight line to the gradual decrease in cases turning into hospitalisations. (You can see the fit here if you’re interested.) I think this is probably optimistic: the vaccination rate has slowed a bit in recent weeks, and we’ve already vaccinated the most vulnerable and therefore most hospitalisable. The fit also predicts literally zero hospitalisations per case by about September, which obviously doesn’t make sense: not everyone will get vaccinated, and the vaccines aren’t perfect.
- Used that decreasing linear fit to transform cases to hospitalisations. Since there’s an assumed 10-day delay, we can already ‘see into the future’ using testing data. After that, I used the extrapolated case numbers with the extrapolated case-to-hospital ratio.
This is by no means a perfect model, but I don’t think any part of it is obviously wildly wrong.
And I think it means we should do something, rather than just letting covid cases carry on doubling every couple of weeks. We’ve seen from previous waves that every day you delay action, the virus gets exponentially ahead. The sooner we act, the shorter and less painful the action will need to be.
Additionally, this time we have vaccines—and we know that double doses of them provide excellent protection against Delta. We can immunise an awful lot more people in just a few more months, and radically decrease covid’s options. And, perhaps more importantly, a huge epidemic in a highly vaccinated population like the UK’s is a a dangerous experiment which risks breeding a properly vaccine-resistant variant, taking us, and potentially the whole world back to square one.
Of course, this may be wrong. It’s a dumb model I threw together in R. I am not an epidemiologist. But are we willing to bet the NHS, the economy, the summer, and maybe even the world’s fight against covid on this simple projection being a wild overestimate?