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One-jab efficacy questions

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D_W

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There was no evidence that Covid 19 was about to cause a global pandemic either until it happened.
How about the spread in China that was covered up? That was pretty clear evidence. Just as all of the data so far is clear that the vaccines control all of the variants.

Washington state has tracked 1.2 million people so far, and found only 100 positive pcr tests among those vaccinated, and only 10 hospitalized. Out of 1.2 million. I'm sure all of the variants are present there. The virus isn't fast mutating.

It's as if reality is just too positive for people.

Vaccine rate here is over 90% while the news was obsessed with claiming only half of the population would take the vaccine because !trump!. What they did to claim that was count the half of the respondents who said yes as a yes and count the people who said they would consider it if it worked without harm as no. That was about 30-40% of respondents. Of course more than that yet have taken the vaccine, which was predictable. People got hysterical over some supposition that would never happen.

If there ever is a new variant that isn't controlled, we'll know within days. Until then, to ignore actual data is foolish.
 

TominDales

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Thanks for your really helpful reply, TominDales.

That US study was after two doses, right? Johnson was talking about the effect of the first dose, and it was his stats relating to that that got me wondering - most of us who are eligible are in the one-dose state at the moment and many will be for some time to come as we unlock, schools are already back, and it's looking pretty busy out there at the moment (Easter hols, good weather etc.), and the Kent variant's much more easily transmitted than the original form we had (which by all accounts spread easily itself). Certainly, the broader context looks much better in terms of vaccinations and treatments.
OK this is a hard question to answer with any precision as there are 3 variables, Transmissibility (as measured by R0), Vaccine efficacy %, and vaccine coverage %, all of which have uncertainty. Back in October 2020 it was thought that the vaccine efficacy needed to by 60% with 100% coverage and r0 of 2.5 to3.5 to prevent an epidemic. Efficacy needed to be 70% if coverage is only 75%, to prevent an epidemic and 80% efficacy to suppress the epidemic.

The R0 is very difficult to measure, for 1918 flu it was estimated at 1.4 to 2.8 with an average of 1.8, for measles its given an average of 12-18 but the range is 4-200. So its hard to pin down R0. For Covid its in the rand 2.5 to 5.7. Wuhan variant average of 2.8. if Kent is 50% higher then it would be in the 4.2 range but with an uncertainty.
The good news is that the vaccines seem to have >60% efficacy for the new variants, which means they are capable of supressing the epidemic is full rolled out.

From this it can be seen why the UK is prioritising 1st vaccine roll out as getting coverage up with a vaccine that has efficacy of 70% for 1st dose is the best way to supress the epidemic and prevent deaths. the second dose is primarily about extending immujnity to 12 to 18 months, however eventually the 2nd dose will help in eliminating the epidemic.

The consensus of opinion is that herd immunity is now unlikely for Covid19 and that we will have ongoing bouts, similar to measles etc so ultimately we will have to get to a situation where everyone is vaccinated and childhood vaccination are the norm. This means that until that happens, schools will have to continue regular testing of students to keep the virus supressed.

As I've commented earlier, the mix of measures today, including, rapid testing and isolation of infected individuals, vaccine roll out, and sensible social distancing should enable us to open up the economy and live with the new variants. We will have to do this until we achieve ca 85% of the population vaccinated.
Sorry not be be clearer - my view is we have the tools to get on top of the epidemic, but it will take several months to get there.
 

Chris152

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Thanks again TominDales, very clear. I really don't want to take more of your time but, in case your patience isn't already at the limit, I rephrased the second question with Ozi this way, ignoring the broader context:
Given that one dose reduces likelihood of infection by about 60% and that the Kent variant is 50-70% more readily transmitted, in the same narrow scenario (say, sitting across the table from a contagious person) are my chances of contracting the disease now (4 weeks after first dose sat opposite a Kent variant carrier) about the same as they were a year ago with the old variant and no jab?
So I'm not thinking (to use Ozi's term) at the population level, but at an individual level of risk.
 

TominDales

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Thanks again TominDales, very clear. I really don't want to take more of your time but, in case your patience isn't already at the limit, I rephrased the second question with Ozi this way, ignoring the broader context:
Given that one dose reduces likelihood of infection by about 60% and that the Kent variant is 50-70% more readily transmitted, in the same narrow scenario (say, sitting across the table from a contagious person) are my chances of contracting the disease now (4 weeks after first dose sat opposite a Kent variant carrier) about the same as they were a year ago with the old variant and no jab?
So I'm not thinking (to use Ozi's term) at the population level, but at an individual level of risk.
Simple questions but actually hard to answer at all precisely but as a rough guide, I'd say it was 100% probability of catching it last year vs 24% for Kent Variant this year, but this year your chance of dying has been reduced to nearly zero.

Simply put assume you spent a meal next to a person last year indoors who had Covid, you would be close to 100% likely to get it and depending on your age your age the case fatality rate CFR as of August 2020 was about 4% for men but 56% for men over 80. Age has a huge bearing on severity and CFR. Bear in mind that CFR is very hard to measure with any degree of accuracy.

If you sat next to a similar person this year (with the Kent variant) on having had 1st does of vaccine at 60% efficacy, then you would have a 40% chance of catching Kent variant. But there is likely to be a 40% chance that person was vaccinated so your chance of getting covid is reduced further to about 24%. Furthermore your chances of dying drop to near zero.

That early scenario is a bit biased as we assumed 100% transmission which cant be increased, so lets take another case, a bit more of a race between the two Covid variants. Suppose you sat some way away from the person and you are in a younger age group so that your chance of getting covid was reduced to 50%. we can assume that last year you were 50% likely to catch it, whereas the Kent version would be 70% more transmissible, so your likely chance of infection pre-vaccine goes up by 50*70% ie up by 35%, giving you an 85% chance of getting before vaccination, but after vaccination that 85% reduces to 51% (85%x60%) and down to 30% if when taking into account that your neighbour may have been vaccinated (40% probability depending on age). Your probability of dieing is still near to zero. Also once vaccine roll out has hit 80% of the population, your chance of getting new variant covid would fall to near zero.

Statisticians tend to give answers in terms of groups of people. this link has a set of apps - mainly us based that give you your chance of getting COVID. there case case is if you dine out with a group of 10 people in Boston USA chances of 1 person getting Covid is 30%. What’s your risk of catching COVID? These tools help you to find out

If you sat next to them outdoors, your chances reduce 18 fold, ie down to 5% last year and about 1.5% this year. Hope this helps.
 

TRITON

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Let us know how it goes, mine was totally painless injection and just a slightly sore arm. Hope yours is the same.
Yes, thats same too. Sore arm for the last 48h, which is now pretty much akin to a stiff shoulder.
But by sore i dont mean agonizing, more like someone punched you there and you dont notice unless you move it.

Another step forward and i'm happier its been done. Now hopefully things might start to improve, but i fear this could be like the flu jab and a yearly thing.
Still better that the virus itself, as with the flu which always hits me quite hard.
 

profchris

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If you sat next to a similar person this year (with the Kent variant) on having had 1st does of vaccine at 60% efficacy, then you would have a 40% chance of catching Kent variant. But there is likely to be a 40% chance that person was vaccinated so your chance of getting covid is reduced further to about 24%. Furthermore your chances of dying drop to near zero.
Can I ask for clarification, as you clearly know more about this subject than most, including me.

My understanding (which could be wrong) is that 60% efficacy means that 60% of those vaccinated have enough antibodies to prevent infection serious enough to cause illness, while 40% do not.

If I got that right, then for an individual whose antibody levels we don't know, your example is correct. However, if we know their antibody levels, then either they won't (if they are in the 60%) or will (if in the 40%) catch the Kent variant. [Caveat, I know this is simplistic if only because catching the virus seems to depend on how much viral load you receive from the infected person, but I recognise you are simplifying for those with no strong statistical training]

I think my point is that statistics don't tell us exactly at an individual level, though they do at a population level. If so, a better way of understanding it would be "If a group of 10 of us, all vaccinated, sit next to the infected person, probably four of us would become infected but we can't say which four."

Encouragingly, my own reading suggests that the tentative conclusions which are being drawn from the data is that a single dose of any of the vaccines reduces the risk of infection requiring hospitalisation to nearly 0%, and the risk of infection causing serious illness below that level to less than 20%. And this is the risk if you are exposed to a sufficiently high viral load to cause infection, which depends on who you meet, where you meet them, how long you spend together, etc.
 

TominDales

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Can I ask for clarification, as you clearly know more about this subject than most, including me.

My understanding (which could be wrong) is that 60% efficacy means that 60% of those vaccinated have enough antibodies to prevent infection serious enough to cause illness, while 40% do not.
You are quite correct, statistically my answer does not hold water as we don't know the transmittable of the mystery neighbour (they could be highly infectious or infectious at all which is why I chose to give some specific scenarios for this 'hypothetical virus race' concerning a the person sitting next to Chris123 to give a feel to the answer to his questions.
Simply put, Chris is asking are we better off now than a year ago, given the Kent variant. His question is a good one as its trying to put in personal terms what the comparative risk is. I think those two scenarios allow for us to make that simple comparison. Its not a mathematically robust answer but I think its give as a rough picture.

To do the risk analysis properly lots of factors have to be taken into account and that point it gets pretty tricky, but I think Chris is after a rule of thumb are we in a better situation or not and my view is yes and if you take any situation that is compatible with last year the effect of the vaccine is highly significant.
The link is to a Nature article has some good statistical models that allow for a better analysis if you want to go into it properly.
I know a bit about the vaccines as at my work, is the UKs flagship programme on the new variant vaccines, but I don't pretend to know much more than the rest of this forum as the statistics gets very specialised.
 

Chris152

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a single dose of any of the vaccines reduces the risk of infection requiring hospitalisation to nearly 0%, and the risk of infection causing serious illness below that level to less than 20%.
I'm still struggling to understand this, in spite of Tom's helpful answer - maths was never my strong point, to say the least.
But in relation to what you wrote, Whitty was on tv just now with a diagram showing a reduction in hospitalisations after one jab of 80% (to 20%) (see pic).
The stats seem to be the same as Johnson described a few weeks ago, in which he also described an 80% reduction in hospitalisations and an 85% reduction in deaths. So I'm still stuck with the idea that if you as an individual are unlucky enough to contract the disease, there's only a 20% reduction in the likelihood of ending up in hospital and only a 15% reduction in the likelihood of death?
I'm caught between my own dodgy maths and reassurances from people who say I shouldn't be!

ps I'm pursuing this for two reasons: first is personal, I have two kids in school and I can't help but think as cases rise, there's every chance they could bring it home; second, as we unlock, what can we expect next and to what extent do we as individuals need to be careful.


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Terry - Somerset

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Surely the chances of infection are a function of two issues:
  • the probability of a vaccinated individual being able to transmit the virus. The extent to which the vaccine inhibits transmission is still somewhat unknown (or unpublished!).
  • the effectiveness of the vaccine in preventing infection, serious illness and death
So a more realistic assessment of personal risk in (say) a restaurant may be as follows:
  • risk that an adjacent individual is currently infectious - approx 1 in 350. This is a very simplistic average with could vary materially.
  • risk they are infectious assuming one jab - approx 40%
  • risk that we are sufficiently close for sufficiently long for me to be infected - (say) 25%
  • risk of me catching covid given I have been vaccinated - 40%
  • risk of hospitalisation (say) ~5% (65+ years old)
  • risk of death (say) ~5%
Deliberately simplistic I know - my personal risk were restaurants open today (sadly they are not) would be: 0.3% x 40% x 25% x 40% x 5% x 5% = 1 in 3.3m chance of death. More chance of death driving to/from the restaurant!!
 

TominDales

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@TominDales my partner falls right into the affected category for blood clots, uses the contraceptive pill and has a family history of strokes, biggest killer in her family and several survived but long term disabled.
I'm sorry to hear that. It is a worrying time for you both. This is probably something she should speak to her GP about. They may be able to get her onto a list for the Pfizer or another alternative vaccine. I suspect there will be rules on who can get what as they wont want a free for all, but as time goes by and the risks get better known then the role out may get nuanced. A good GP will understand, but they may not have much discretion at the moment - the NHS is trying to keep the AZ programme running. Its a situation, as Covid can cause increase risk of stroke in some patients and the contraceptive pill also has contra indications of which stroke is one with some type of contraceptive. Given how few cases of blood clots have emerged it may take a while to understand what is behind it. In the meantime there maybe precautions that you and the wider family can take to reduce risk of infection until the situation is clarified.
My partner had a nasty dose of pleurisy last year just before covid and our family including the kids took extra precautions until she was fully recovered. It made her feel a lot safer even if it didn't help her medical condition she was grateful for it.. Best wishes Ton
 

TominDales

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I'm still struggling to understand this, in spite of Tom's helpful answer - maths was never my strong point, to say the least.
But in relation to what you wrote, Whitty was on tv just now with a diagram showing a reduction in hospitalisations after one jab of 80% (to 20%) (see pic).
The stats seem to be the same as Johnson described a few weeks ago, in which he also described an 80% reduction in hospitalisations and an 85% reduction in deaths. So I'm still stuck with the idea that if you as an individual are unlucky enough to contract the disease, there's only a 20% reduction in the likelihood of ending up in hospital and only a 15% reduction in the likelihood of death?
I'm caught between my own dodgy maths and reassurances from people who say I shouldn't be!

ps I'm pursuing this for two reasons: first is personal, I have two kids in school and I can't help but think as cases rise, there's every chance they could bring it home; second, as we unlock, what can we expect next and to what extent do we as individuals need to be careful.


View attachment 107582
Its confusing, my interpretation of these figures is;
If you are aged 80+ then the chance of hospitalization has fallen to 20% of what it was ie 80% reduction. and deaths have fallen by 85% from what they were. Given the the Case fatality rate (CFR) for 80+ bracket was 56% last summer ( I think its much lower now due to better treatment) then I suppose the CFM for 80+ years olds is now about 7.5% (15% of 50%) and for the average male its dropped from 4% to 0.6%. its very low people below the age of 40 in any case. These figures seem conservative as I'm read elsewhere that fatalities are virtually zero after 4 weeks, as recent deaths seem to be in people who caught covid within two weeks of the vaccine. There have been studies of care homes that are encouraging. I'll see if I can find them - just need to get a bit more gardening done tonight or I'll get shouted at ....
 

Rorschach

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I'm sorry to hear that. It is a worrying time for you both. This is probably something she should speak to her GP about. They may be able to get her onto a list for the Pfizer or another alternative vaccine. I suspect there will be rules on who can get what as they wont want a free for all, but as time goes by and the risks get better known then the role out may get nuanced. A good GP will understand, but they may not have much discretion at the moment - the NHS is trying to keep the AZ programme running. Its a situation, as Covid can cause increase risk of stroke in some patients and the contraceptive pill also has contra indications of which stroke is one with some type of contraceptive. Given how few cases of blood clots have emerged it may take a while to understand what is behind it. In the meantime there maybe precautions that you and the wider family can take to reduce risk of infection until the situation is clarified.
My partner had a nasty dose of pleurisy last year just before covid and our family including the kids took extra precautions until she was fully recovered. It made her feel a lot safer even if it didn't help her medical condition she was grateful for it.. Best wishes Ton
There is no option to choose your jab and to be honest we don't know the data on the other jabs yet either as they have not seen widespread use in younger people.

Honestly though, we aren't worried, we will be back to normal activities as soon as possible, we have a holiday planned for literally the day the hotels open. We don't live in fear, we enjoy life, it's far too short to worry about what could happen if you go outside.
 

Woody2Shoes

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I take it you're not thinking of yourself as one of these 2 or 3 billion ;)

Is it ?.
Some cities are densely packed, but much of the planet is uninhabited. in fact great swathes of land have nobody living there.
Here is a link to the Wikipedia page for the Earth. Earth - Wikipedia
According to this source, land occupies just over 29% of the Earth’s surface, or 148,940,000 square kilometres. There are 1,000,000 square meters in a square kilometre, so there are 148,940,000,000,000 square meters of land on the surface of the Earth. That’s approximately 150,000 billion square meters of land.

According to this source, World Population Clock: 7.5 Billion People (2017)
there are approximately 7.5 billion people currently living on earth.

If you divide 150,000 billion square meters by 7.5 billion people, you get about 20,000 square meters per person. You can think of that as a square about 140 meters on a side. That’s enough for a very nice house and a big garden.
I think that your simplistic arithmetic fails to take account of the fact that large areas of the land are effectively uninhabitable - to a greater or lesser degree - and climate change will increase the uninhabitable-ness of many places (which will either disappear underwater or simply be too hot) :oops:
 

Woody2Shoes

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This variant nonsense is the media's last gasp at getting a scare out of people. I say that because there is no evidence that a variant that actually evades vaccines will develop any time soon.
Absence of evidence is not evidence of absence. The whole point is, nobody knows what mutations will happen (other than that we know they will) and what the effect of those mutations might be - Covid came as a surprise to governments all round the world, after all. We also know that vaccines exert an 'evolutionary pressure' on viruses. Yes, we're all better prepared than we were a year ago, but variants can/could still cause us all a lot of trouble (I don't need 'evidence' to believe that!).
 

Woody2Shoes

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So here we go again, as we get the numbers down and begin to get life more normal here in the UK with a high percentage of vacinations what does the government decide to do, lower the drawbridge and allow international travel with some hair brain traffic light system even with the virus staring them in the face. It could work if there was 100% compliance and measures in place to prevent onward travel but there won't be. So nothing to stop people going to a green country and then having their holiday in a red country and returning via the green country or going to a green country and coming into contact with others who have come in from a neighbouring red country so why lower the drawbridge just when things within are settling down and we have a fair measure of control.
Just spoken to an aquaintance who flew into London from New York last week - but "had to come via Madrid", presumably to take best advantage of all the various rules that differrent countries are dreaming up.
 

TRITON

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I think that your simplistic arithmetic fails to take account of the fact that large areas of the land are effectively uninhabitable - to a greater or lesser degree - and climate change will increase the uninhabitable-ness of many places (which will either disappear underwater or simply be too hot) :oops:
I didnt say it was perfect. And that said some people from hotter climates find the UK too cold and vice versa.
" simplistic arithmetic"
Its not my 'simplistic' arithmetic, go criticize wiki, its there I got the info from.

Besides the entire thing was tongue in cheek, obviously some areas arent ideal because it would obviously include Death Valley and other deserts, or 1/2 way up mount Everest. I think you're being a tad overly critical like there bud.
 

Blackswanwood

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Just spoken to an aquaintance who flew into London from New York last week - but "had to come via Madrid", presumably to take best advantage of all the various rules that differrent countries are dreaming up.
Aren’t the rules the same for arriving in the UK from Spain and the US?
 

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