QUICK THREAD ON VACCINES & DELTA: Friday's @PHE_uk report said that viral load in infected vaccinated people was similar to that of uninfected people.

As has been pointed out by others, this does *not* mean all is lost and vaccines don't work.

10 tweet thread explaining why!
1. when you get a PCR test, they measure how many "cycles" you need before getting a positive signal. The more cycles you need, the weaker the original signal.

Lower numbers for "cycle threshold" (CT value) are thought to indicate higher viral load at the time test was taken.
2. In Friday's report, PHE report that CT values were similar between vaccinated and unvaccinated cases for both Alpha and Delta.

They conclude that once infected there "is limited difference in viral load" bewteen vax & unvax.

So how bad news is this?
3. Firstly, remember that NHS Test & Trace gets PCR cases from mostly *newly* symptomatic people. So this means that in the *early* days of symptomatic infection, a vaxxed person could be as infectious as an unvaxxed person.

BUT
4. Other studies have shown that vaccinated people get over infection more quickly - unsurprising since vaccination basically gives your body a massive head start in fighting Covid.

So vaxxed likely infectious for *less long* than unvaxxed.

medrxiv.org/content/10.110…
5. If this holds, then if you *randomly* sample people at any stage of their infection, you should see that *overall* CT values are lower for vaxxed people than unvaxxed (because green CT values are lower than red ones for most of the PCR detectable time).
6. This is exactly what the REACT study showed which does random testing and so isn't finding people mainly in the first few days of their symptomatic infection. (also includes asymptomatic people... and vaxxed more likely to be asymptomatic?)

7. Then of course, you are also much less likely to get syptomatic infection in the first place if you are fully vaccinated - 80% *less* likely according to PHE.

(and much less likely to need hospital if you do get infected).

So what does this mean?
8. It definitely means that vaccinated people who test positive should be isolating during their first week of infection *at least*. Personally I think vaccinated contacts should still isolate for a week - but *at least* test themselves every day for a week.
9. But it also definitely means that vaccination is better than being unvaccinated at preventing infection and then clearing infection if you do still get infected.

So get vaccinated, don't despair but get tested if you get symptoms and isolate if you're positive. /END
PS H/T to @kallmemeg for her tweet thread on this which I've just adapted a bit!
sorry - typo! that should say red CT values lower (and so viral load higher) than green CT values.

Note that the Y axis in figure above is opposite direction than the one in earlier PHE graph.

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More from @chrischirp

8 Aug
QUICK THREAD on English Covid situation (6 tweets).

1. Overall cases have stopped going down and have been flat over the last week.
2. Most regions are flat, but NE continuing to decline a lot from its large peak and some regions Yorks, E Midlands, SW) are going up slightly.

Similar patterns nationally & regionally in positivity rate.
3. Cases are now very concentrated in young adults. Cases in under 15s have dropped a lot since end of term - partly fewer cases and partly less testing.

Cases dropping older adults too but more slowly than in children.
Read 6 tweets
30 Jul
QUICK THREAD on Vaccines:

Vaccinations have slowed down, esp 1st doses. About 6 million adults left without a first dose & 9 million on just one dose.

Will take about 6-8 weeks to give those 9m a second dose. And we need to work on making it easy for 6m to get their 1st.
Overall we still have 30% ish of population unprotected by vaccination. Note that about 20% of pop are children not eligible for vaccines (yet!).

Wales furthest ahead with its vax programme, followed by Scotland.
67% of 18-24 yr olds in England have had their first dose which is promising.

But more worryingly quite a lot of 40-49 yr olds still need their 2nd jab.

In younger adults, women more likely to take up vax than men.
Read 5 tweets
30 Jul
THREAD: latest covid situation in UK (mainly England) and what I think is going on...

TLDR: I *do* think there has been a recent drop in transmission, due to combo of different things. Might not be quite as big as seems and might not last.

(22 tweets)
2. UK cases have dropped quite a bit since 19 July, but gone up a bit again over last couple of days. 29K cases today keeps it higher than it was earlier in week but lower than last week.
3. Different patterns for each nation. But Scotland has been dropping consistently since early July in cases & positivity rate. Positivity rates still quite high though.

England dropping since 19 July & also seeing declines in positivity rate. It's not just fewer tests.
Read 23 tweets
24 Jul
LONG THREAD: so I said yesterday I felt that the schools study in daily testing instead of isolation of pupils had been misreported. I don't think study tells you very much except that neither isolation or testing are working very well in schools.

Here is why...
What does study do? It takes 201 schools and assigns 99 to be "controls" - ie continue as normal, asking contacts of children with new confirmed covid to isolate for 10 days. The other 102 schools get assigned to "daily contact testing" (DCT) for contacts instead of isolation.
The hypothesis was that children in the DCT (testing) schools would miss fewer schools days than those in the control (isolation) schools without impacting 'too much' on transmission of covid.
Read 26 tweets
23 Jul
LONG COVID THREAD:

The people running the BBC Horizon "Great British Intelligence Test" challenge on over 80,000 people took the opportunity to see if they could detect any differences by whether people had had covid or not...
2. They did this because of increasing concern over reoprted cognitive impacts of long covid - but more evidence is badly needed. Image
3. What they found was significant cognitive deficit for people who'd had covid compared to people that hadn't, after controlling for things like age, education, sex, first language etc.

The degree of deficit was worse the more severe the initial covid infection had been. Image
Read 13 tweets
22 Jul
15 Tweet THREAD on current cases & trajectory:

Cases this week have been bit lower than many expected (inc me!). Have we peaked?

Here are my thoughts for what they're worth...

TLDR: lots of possible things combining. I don't think this is the peak.
2. we know PCR testing capacity is stretched. Test & Trace reporting longer test turnaround times and results taking longer to make it to the dashboard.

Looking at results by date of test to 5 days ago (17 July), things still increasing everywhere but Scotland.
3. Looks as if the combined dampening effect of Scotland being knocked out of Euros, school term ending and final opening delayed has helped bring cases down. Which is very good news.

Term ended in Wales on 16th July and today in England. That will bring cases down from now.
Read 15 tweets

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