All Wales infection rates had been falling steadily for a while and despite the Christmas blip the trend seems to be establishing itself again but if you watched the press conference on Wednesday there was distinct nervousness whenever North Wales was being talked about so why might this be so.
First off what do we know
In December when South Wales rates fell the North continued to rise
The new variant has risen from 20% to between 60 and 90% of new cases in the N but was lower in the South
The new variant has an R value of between 0.4 and 0.6 higher than the original.
So in essence we have not one but two pandemics running in parallel. The first stain is the one that is dominant in the South but as Welsh Government evidence shows the new strain is starting to get a hold in the area. The second in the North had fewer infections to start with so more susceptible individuals. In this area the new variant appears to have arrived before schools closed and established a foothold. Now we have introduced stringent measures that have reduced R levels by about 0.3-0.4 since Mid December.
So in very simple terms this would place R for the old variant about 0.75 and new at about 1.1. Lets look at this on a graph. First up a scenario where there are 900 cases of the old and 1 of the new. Here we see a rapid falling off of infection rates as the old variant (yellow) can't reproduce combined with a slow growth of the new (orange) before eventually it becomes dominant and then starts to grown the total number of infections again.
Now we can restart with a 20 new and 100 old this is roughly where N Wales was in terms of proportions in Early December.
Now the story is very different instead of taking about 18 cycles to begin to grow the total rates of virus are on an upward trend in half the time. But OK you might say there are lots of different factors at play here it doesn't necessarily mean anything but now look at the data from Wales by Health Board area in December.
I've used this graph before and the mixing on Christmas Day muddies the water a bit but with Schools closed on the 11th most of the lockdown benefits kicked in at that point. Now allow the lag of in home infection to kick though and look at the curves between the 15th and 28th. In the South there is steady decline in the North (orange) there is a steady growth.
And this is why the professionals are nervous.
They know that rates in the North have continued to rise. This is entirely consistent with R for the new strain being marginally above one. So if its above 1 in the North is it also likely to be above 1 in the South all be it from a lower base of actual infection.
Which leads to the key question. Is the southern fall completely genuine and will continue or is the downward trend masking a replacement of infection by the new strain which is expanding unseen in a generally falling overall total?
Recent ONS studies are suggesting that the variant is growing in the South. How much is a key question. We also don't know how fast the spread will be. Can we assume that those infected in Nov/Dec will help reduce R by breaking pathways? Will the public respond and self lockdown further?
The early indications in Jan were not promising Christmas was a national super spreader event given how many new infections occurred in tests between the 29th and 31st so the base line has been moved up. Tougher measures in supermarkets will no hopefully move things forward.
But all eyes are on Wales at the moment the new variant is here in significant volumes and we have been in effect locked down for over a month. If rates in North Wales don't start to fall soon scientists will have to reach the evidence based conclusion that the current measures are not enough in the face of the Kent variant.
The only question then is where is the rest of Wales on that replacement and growth graph?
Now more than ever we need to think carefully about every single interaction we make.
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