AstraZeneca currently thought to cut transmission by 50%

[salmonskinjerky]

I can't link to the article because its part of a Guardian liveblog, so I'll paste it here;

Vaccines do not completely stop transmission, JCVI member says
Covid-19 vaccines do not completely prevent transmission, Prof Anthony Harnden, deputy chair of the Joint Committee on Vaccination and Immunisation (JCVI) has said.

He told BBC Breakfast on Sunday that while they appear to reduce transmission by about 50%, vaccinated people can still get the virus and spread it to others.

He added:

There’s some good evidence now from Public Health England and from the Oxford/AstraZeneca trials that the vaccines do prevent transmission.But they don’t completely prevent transmission. The figures are still being calculated but it’s in the order of 50%.

So, there will be some reduction in transmission, no doubt at all, but it’s still possible, even though you’ve been vaccinated, to get infected, have no symptoms and transmit it to others. That’s why it’s important that all those who get vaccinated still stick to the rules.

So, there will be some reduction in transmission, no doubt at all, but it’s still possible, even though you’ve been vaccinated, to get infected, have no symptoms and transmit it to others. That’s why it’s important that all those who get vaccinated still stick to the rules.

Is this bit a continuation of Harden's analysis from the live blog or is it your own, op?

I've seen it said on here that the vaccine reduces transmission to a "vanishingly small possibility". The vaccine seems to protect the person who receives it really well, which is great, but clearly a lot of people have an unrealistic idea about the level of protection they offer to others.

@FourTeaFallOut

Its a continuation of the liveblog

Both paragraphs are Harnden’s

Brilliant, thanks.

It would be interesting to know some of the parameters around the 50% figure. After 1 or 2 jabs and how long after the jabs? Is this the upper limit in protection from forward transmission or some limbo point that follows any time following the first jab?

I don't expect you to know op but I'm just interested to see, particularly after the snippet in the Guardian yesterday about 1 in 25 in hospital with covid jab have had a vaccination only to read further and find that the vast majority of these patients will have contracted it mere days before or after the jab. It's like blaming dough for not being bread before you've baked it.

In any case, I think 50% is pretty good. If the jab reduces infection by say 70% and then those who remain capable of incubating the virus are now half as likely to transmit it - then that's brilliant - so long as I have understood that correctly.

What about if the person you are seeing is vaccinated too?
I have had both doses of AZ as have my parents. Surely it should be fairly safe to see them now?

@Alfaix

What about if the person you are seeing is vaccinated too? I have had both doses of AZ as have my parents. Surely it should be fairly safe to see them now?

I would've thought so, if sufficient time has passed since you all had your second dose

So the idea of ‘vaccine passports’ as a means to prove that you’re not a risk to others is a bit silly then.

@Alfaix
You would think so.
If I'd had both doses and my parents were still alive I would be seeing them.

@FourTeaFallOut

Brilliant, thanks.

It would be interesting to know some of the parameters around the 50% figure. After 1 or 2 jabs and how long after the jabs? Is this the upper limit in protection from forward transmission or some limbo point that follows any time following the first jab?

I'm assuming they would've mentioned if the figure was based on one dose only. Maybe more detailed information will follow, I'd imagine there will be questions about this at the next briefing

It doesn't matter if you have all been vaccinated, you still have to follow the guidelines. This has been made clear since the beginning that masks and sd'ing will still be required.

@bumbleymummy

So the idea of ‘vaccine passports’ as a means to prove that you’re not a risk to others is a bit silly then.

I was thinking the same.

Even 50% reduction is still quite concerning though. If the original CV has R of about 3 without restrictions and some of the mutant strains have R up to 5, then am I right in thinking that the R rate will be 1.5 - 2.5 for vaccinated people (without restrictions)? So still well above 1

Even 50% reduction is still quite concerning though. If the original CV has R of about 3 without restrictions and some of the mutant strains have R up to 5, then am I right in thinking that the R rate will be 1.5 - 2.5 for vaccinated people (without restrictions)? So still well above 1

No because you are ignoring that the contraction of the virus is reduced by 70% with the jab before you get to the remaining 30% who now only transmit the virus at half the rate they would have done without the virus.

Without the vaccination! (Not virus)

Am I being thick?
So after 2 jabs you have, say 90% protection against getting it.
So it's the 10% that have jabs and still get it that can pass it on. Of those 10%, half might pass it on?
So its cutting transmission to 5% from vaccinated people?
Or is that wrong?

@SpiderinaWingMirror

Am I being thick? So after 2 jabs you have, say 90% protection against getting it. So it's the 10% that have jabs and still get it that can pass it on. Of those 10%, half might pass it on? So its cutting transmission to 5% from vaccinated people? Or is that wrong?

I'm fairly sure that the 90ish% protection was from symptomatic disease rather than infection? The trials didn't look for asymptotic cases. Correct me if I'm wrong.

*asymptomatic

Sadly not Spider. The 90% (or whatever) protection refers to your protection from getting seriously ill whether or not you get it, relative to the risk you would have had of you hadn’t been vaccinated.

What this c.50% figure means is that a sizeable minority of that 90% will still be getting and transmitting the virus, they’ll just be better able to defend themselves.

Do you know, this kind of wooliness really annoys me. Surely if Prof Anthony Harnden can say with some certainty that the vaccines reduce transmission by 50% then he must have a pretty damned good idea how they came to that conclusion and what figures they are using. We have such piss poor news sources, surely someone asked this question before they got excited about running with 50% accompanied by grave tones? ... Bloody ridiculous half-arsed journalism again.

Wearing a seat belt does not guarantee you won't be killed in a car crash. It makes it less likely. Ditto for having a car with airbags, sticking to the speed limit, driving to the weather conditions and paying attention. Do them all for the best risk reduction. Clearly on many occasions you can drop some or even all of those, and still not have an accident. Or have an accident in which you don't die. But it still makes sense to do all of those things as much of the time as possible.

Being vaccinated does not guarantee you won't die from Covid. It makes it less likely. Ditto for being careful with social distancing, wearing a mask, keeping premises ventilated and washing your hands. Do them all for the best risk reduction. Clearly on some occasions you can drop some or even all of those, and still not catch Covid. Or catch Covid and not die. But it still makes sense to do all of those things as much of the time as possible.

Of course, if you are in an accident, it's not only you who might die, it's other people as well. So you should do all those car safety things to protect other people as well as yourself.

Of course, if you catch Covid, it's not only you who might die, it's other people (who you pass it on to) as well. So you should do all those Covid safety things to protect other people as well as yourself.

Car safety measures become more important when there's a lot of traffic on the road. You might be able to relax some of them on empty roads.

Covid safety measures become more important when there's a lot of Covid in the community. You might be able to relax some of them when Covid levels are low.

I had dose 2 3 weeks ago but my parents only had dose 2 on Friday. I actually vaccinated them for dose 2 which was nice.
We’ll leave it a couple of weeks then.

I actually think that “it’s about 50%” is probably a decent summary of the data available. There’s been several different studies using different methods but they’re all a bit flawed and involve extrapolation from incomplete data. They all suggest that the vaccines give a significant reduction in transmission but that it’s less than the reduction in illness and death, but the error bars are really large.

Do we think that this will stop people trotting out “actually the vaccines only stop you having symptoms, they don’t stop you passing it on” on every sodding vaccine thread? Do we hell.

No it's bullshit. Is it 50% transmission among the entire vaccinated cohort or 50% transmission of those who get coronavirus despite a vaccine? For instance, is that clear yet?