COVID-19: The vaccine's success means we have to look at the data differently

·4-min read

Economists have a phrase for it: a heuristic.

It's a kind of rule of thumb, and we humans tend to develop mental heuristics to help guide us through everyday life.

If you burn your finger on your frying pan, the painful lesson is: don't do it again! These kinds of Pavlovian responses are quite easy to learn but quite hard to shake.

And throughout COVID-19 we've developed something of a national heuristic when it comes to this disease, which runs as follows: if cases are on the way up, that means hospitalisations will follow, and so too will deaths.

In the first and second waves of the disease, this heuristic proved pretty useful, as we could get a sense from the case data about how pressed the NHS would be in the following weeks, and in turn how terrible the mortality situation would get.

However, this heuristic no longer seems to apply to the situation we're in at the moment. Because so many people are vaccinated, the relationship between cases and those worse outcomes has shifted.

The problem is that we're only learning this tentatively as we go on, and, as I say, heuristics are quite hard to shift (once you've burnt your finger on a pan that was hot the last few times you touched it, you might be reluctant to touch it again).

It comes back to the good and bad news vying with each other in the COVID-19 data narrative.

The bad news is that cases are rising, and rising pretty fast. True: the growth rate is not quite as fast as it was in previous waves, but nonetheless, it's climbing at a fair snip, up by nearly 5% in the past fortnight or so. Extrapolate that growth rate forward a few weeks and it works out at daily case growth of 40,000 a day by 19 July.

Now, it's worth saying that's a very simple extrapolation of recent growth into the future, and it's quite plausible that that growth tails off considerably - especially with the vaccine programme still continuing at pace.

But even so, it raises an awkward question, because we all know what 19 July is, don't we? 'Freedom Day'. Even as the UK is due to remove the last of its lockdown restrictions, cases could be very high indeed. And the nationwide mental heuristic (cases = hospitalisations = deaths) means this could be a tricky message to communicate.

But that's where the good news comes in; because hospitalisation growth is not increasing at the same rate as cases. Extrapolate hospital admissions in the UK, currently at just over 200, a few weeks into the future, and you get a number of 560 by 19 July.

Here's another way of putting it: based on recent trends, cases of COVID-19 on 19 July could be at around two thirds of the levels they peaked at in the winter. But, on the same trends, hospitalisations could be barely more than a tenth of the winter peak (they were running at over 4,000 a day in early January).

The problem, of course, is that we're used to assuming that high cases will inevitably lead to terrible outcomes for the health system. Yet it does look, for the time being at least, as if the link between case growth and deaths has been weakened. Deaths are still very, very low - far lower than they've ever been during a period of case growth as high as it is right now.

Clearly, death is not the only unfortunate consequence of catching COVID-19. There are other complications, including, most notably, long COVID. The disease is not a pleasant one in the slightest.

However, the fact that deaths and hospitalisations are so low is very reassuring indeed, suggesting the vaccines are working effectively.

That brings us to perhaps the most important datapoint of the current era: the case fatality rate.

Throughout most of COVID-19, the CFR, which is the percentage of people with COVID-19 who go on to die of it, has hovered close to 2%. It was 2% for those who got the Alpha/Kent variant over the winter.

But according to Public Health England, the latest CFR for the Delta variant is just 0.3%. This is not, it's worth emphasising, a reflection on the lethality or otherwise of the disease itself (as far as we know, it is somewhat more dangerous for unvaccinated people).

It is a sign that the vaccines are working. Which in turn is another illustration of the fact that the link between cases and deaths is weakening dramatically.

But heuristics are hard to shake.

There has been some consternation this week about the fact that while cases in most other European countries are falling, they are rising sharply in the UK.

And there's no disputing this data. But as that relationship between cases and deaths weakens, we should keep those numbers in perspective.

Hospitalisations remain low. Deaths remain low.

Things could change in the coming weeks. One thing COVID-19 has certainly taught us is to expect anything. But for the time being, the good news is outweighing the bad.

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