[spuz]

Yes variants occur all the time but they don't tend to become dominant. This variant went from 30% of all infections in November to 60% three weeks later. In order for a given variant to supplant all the others and become dominant it must have some characteristics that make it more transmissible. That is why they are particularly worried about this variant.

[raphaelj]

Could it still be that this variant is as infectious as others, but just happens to be the dominant one in the regions where the virus circulates the most, for reasons that have nothing to do with the genetics of the virus?

London and the South East are some of the densest populated areas in the UK, and one could expect exponential growth of infections there while other less populated areas could manage to keep their Rt around or bellow zero. If this strain was more prevalent in these regions, you would also see it taking a larger share of the infections nationwide.

However, the precautionary principle has been the keystone of good handling in the pandemic, so they are right to apply precautionary measures before it's too late. We will learn more about this strain in the next few weeks.

[jsnell]

Look at the prevalence graph in the article, you can see that the new variant has been gradually taking over the turf from the other ones. This cannot be explained by just the founder effect unlike most other cases, since the prevalence was high to start with. It cannot be explained away by a single super-spreader event, since a single event will just cause a single step-change. This has been a continuous process.

It could be random chance or a selective advantage, but then it comes down to just a modeling exercise. How likely is it that this could happen by chance? And it appears quite unlikely: instead the best way to explain the data is a significantly increased transmission.

[lbeltrame]

Is this also taking out potential confounders out of the equation? I believe the currently available data (as opposed to the SAGE minutes, which has the conclusions) is not sufficient to rule that out.

[jsnell]

What confounders would you suggest? Elsewhere in the thread you've been suggesting it's a founder effect. It should be plainly obvious why it's not that, nor something you could attribute to a single super-spreader event.

[lbeltrame]

Reading the latest document out, I can't rule out sampling bias, and the methodology used to gather data is also vulnerable to bias (get samples which are PCR-negative for the S gene, but positive to other genes, which is, by their own admission, a poor proxy).

The confidence intervals shown by PHE on potential increased transmissibility are also very wide (not the ones from the NERVTAG minutes, but the new analyses by PHE).

It needs larger sampling (already doing so, I'm sure) and some biological evidence.

[jsnell]

How would sampling error lead to the relative prevalence growing from 0% to 60% in a smooth exponential curve over 1-2 months?

My understanding on data gathering is that there have been two data sources: sequencing a 10% sample of the positive results, and using the fortuitous point about the three-target PCR tests showing one of the targets as negative for all such tests. Having two data sources is useful since the results from the sequencing are delayed by weeks.

But up to the point where they have both sets of data, the relative prevalence lines up very neatly. In particular, it cannot be that these results are coming from some other variant with the same 69-70 deletion.

(I don't think it's fair to suggest they implied it was a poor proxy in general. They said it was a poorer proxy the further back in time you go.)

Re: confidence intervals, the data they have from the relative prevalence of the new variant has pretty tight confidence intervals (95% CI: 1.34-1.59 R). That makes sense, because the modeling for that is really simple.

The confidence interval for trying to correlate prevalence of the variant vs growth rates is indeed quite wide. But it makes sense, because that's noisy data.

Yes, more data and more evidence will always be great. How many weeks are you willing to wait for it, before putting in new measures? How will that delay affect the epidemic curve if the findings so far are correct?

[spuz]

I don't know enough about epidemiology but I would imagine they have done modelling to determine the likely transmissibility or R number of this new variant to be 70% higher. The probability that this new variant has come to dominate by pure chance must be small.

You are right that London is a densely populated area prone to easy spread for the virus but the same must be true for all variants. This variant started its existence as a single strand of viral DNA and has managed to spread far enough to become the dominant strand against competition from many other well established variants.

[occamrazor]

This variant was not dominant in London some weeks ago, and now is.

[newacct583]

> Could it still be that this variant is as infectious as others, but just happens to be the dominant one in the regions where the virus circulates the most, for reasons that have nothing to do with the genetics of the virus?

Yes, but one assumes that confounding factors like that are fairly easy to isolate. At some point, especially as the growth continues, statistics pretty much rules out other explanations. General consensus is that this is almost certainly more infectious. But sure, there's always more science to do.

[jnxx]

> Could it still be that this variant is as infectious as others, but just happens to be the dominant one in the regions where the virus circulates the most, for reasons that have nothing to do with the genetics of the virus?

That can happen when general incidence is very low, in a small region, or for a short time. But this is not any more the case here, and having this happening by chance is very unlikely.