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I think a lot of the discourse around new rapid tests has become slightly toxic.
They have clear advantages & limitations, and I think I have covered this clearly enough in previous threads.
They have clear advantages & limitations, and I think I have covered this clearly enough in previous threads.
To make clear -
Pros = rapid result so very fast initiation of contact tracing.
Can facilitate decentralised and more frequent testing at scale.
Less likely to detect residual positives
Cons = much lower sensitivity than PCR.
Will miss *a lot* of infectious cases. This is v bad
Pros = rapid result so very fast initiation of contact tracing.
Can facilitate decentralised and more frequent testing at scale.
Less likely to detect residual positives
Cons = much lower sensitivity than PCR.
Will miss *a lot* of infectious cases. This is v bad
To make absolutely clear, in real-world we know they miss *a lot* (about half) of infections that PCR would identify.
& for the record, they *should not* (in my view) be rolled-out for 'test-to-enable' in vulnerable settings such as care homes before we have quality pilot data.
& for the record, they *should not* (in my view) be rolled-out for 'test-to-enable' in vulnerable settings such as care homes before we have quality pilot data.
And, of course, the government *needs* to do a better job at communicating the risks of false negatives.
And it is questionable whether we should be rolling out such a significant and complex intervention if they are not capable of properly communicating the risks involved.
And it is questionable whether we should be rolling out such a significant and complex intervention if they are not capable of properly communicating the risks involved.
And, as happened this week, sending these tests out on mass to care homes with no real standard operating procedure, protocols, or coherent programme (some came without even instructions), is simply unforgivable.
But blindly putting up figures comparing their sensitivity to PCR and saying they detect x% of cases does somewhat remove a lot of the nuance and complexity of their potential uses.
For instance, we know current test and trace is far too slow.
For instance, we know current test and trace is far too slow.
We also know that viral load *generally,* and it is very general and I don't want this to be taken out of context, has a broad correlation with infectiousness.
(There will of course be cases which lower detected viral loads, possibly Ct25, 27, 30 or more, which are infectious.)
(There will of course be cases which lower detected viral loads, possibly Ct25, 27, 30 or more, which are infectious.)
But, we also know that transmission is heterogenous, meaning that most transmission (about 80%) comes from a small proportion of individuals (about 20%). This is likely down to a combination of behaviour and biological dynamics.
The most infectious cases (typically) have the highest viral loads, and are likely to be detected by LFTs
This means that rapid tests, if deployed correctly, could help detect some of the most infectious cases earlier than is possible with rRT-PCR = good for contact tracing.
This means that rapid tests, if deployed correctly, could help detect some of the most infectious cases earlier than is possible with rRT-PCR = good for contact tracing.
We also know that, for example in vulnerable settings, the harms of limited visits and isolation during the pandemic have been devastating. This is also a societal need that needs addressing.
There really are no easy, or good, options here.
There really are no easy, or good, options here.
As I have said for a long time, we do need more data from quality pilot studies before rolling this out on a large scale, particularly if using to facilitate increased contact in vulnerable settings.
And it is pretty damn complex and resource intensive.
And it is pretty damn complex and resource intensive.
And to further complicate things, we probably now need to factor in that the vaccine is on its way to the vulnerable, so is it worth investing in these tests and possibly seeding infections if the population is vaccinated soon?
But, the point is, let's all acknowledge all *advantages* AND *limitations.*
A balanced & reasoned debate is what is needed here. These tests may well have a place, acknowledging the entirely legitimate concerns over false negs & the massive resources required to deploy them.
A balanced & reasoned debate is what is needed here. These tests may well have a place, acknowledging the entirely legitimate concerns over false negs & the massive resources required to deploy them.
