Where claims are being made about the efficacy of COVID vaccines, I wonder in how many of the trials were the volunteers deliberately infected with COVID following the vaccination?
If none, then the claims being made are groundless.
No challenge trials with the Oxford/Astra Zeneca one apparently.
It's my understanding that the volunteers were divided into two groups, those receiving the vaccine and those who were given a placebo. They were all then turned out into the big wide world, and were exposed to the virus or not, as chance would have it and just like any member of the public. All the volunteers were checked for infection, presumably at frequent intervals, and the rates of infection between the two groups compared. If lots of the placebo-receiving group became infected, but hardly any of the vaccinated group were, they calculate the effectiveness of the vaccine.
Provided the numbers in both halves of the trial are reasonably large, up in the tens of thousands, which AIUI they were, it seems reasonable to me.
I gather that one of the issues with these trials is that when infection numbers reduced during the summer, there was less chance of a volunteer being challenged by the virus.
Chris
The counter to that is if those volunteering for the trials were socially responsible people, then they'd be obediently self-isolating and therefore were unlikely to contract COVID so nullifying the claims.
Then that would show in the control group?
You are so clever gareth.
I bet they didn't think of that one!
I'd like to think that in a proper trial issues like this would be addressed. After all, it's not in the drug company's long term interest if they produce a rubbish vaccine and it fails. We saw this happen in the US when a vaccine was rushed into service: it had to be withdrawn. As I expect you know, most drugs developed by so-called Big Pharma actually don't make it to market.
All of which relies on a proven and reliable test ...
I've not heard good things about the testing so far. It seems a little too hit an miss to base anything serious on ?
I think there is one but the ethics of deliberatly infecting someone with a potentially life changing or ending pathogen who may or may not have recieved a vaccination that may or may not be effective make such trials rather difficult.
Yep, trails seem to involve 20,000 or so and the distribution of the first 100 or so cases of infection are used to get the preliminary results.
Why do they need to self isolate?
Sorry, I subsequently realised that what I said about social responsibility would also apply to the placebo group, as nobody would know whether they had the vaccine or the placebo.
I'm not suggesting the results would be wrong, simply that, with a reduced level of infection in the community, then the opportunities for the vaccine to work would be much fewer, which would then lower the statistical significance of the results.
Chris
Yes, well that is sort of the idea of having the placebo group!
I am not aware of any challenge trials for any of the vaccines, yet.
Depends how big the sample is.
I'd hope they have all that worked out long ago. Testing a medicine has been going on for a long time.
What is more, the infection rate amongst the placebo triallists was much lower than the national average. It's hardly surprising that the sort of people prepared to take part in the trial were also the sort of people who would take sensible precautions against catching the disease.
That is exactly why they had to go to places like Brazil, where the infection rates remained high, to carry out the trials.
I do believe this has been done, its called stress testing. The problem is though that most of these were young people, since it might not be ethical to take a vulnerable person and infect them if they were on the placebo. Its a vexed question indeed. I think they rely on the numbers game, since so many have had the vaccine you can pretty much see how protective it is as there would always be a certain percentage of a large cohort who would get it, or be exposed to it. Flue vaccine is less than 75 percent effective but works due to the numbers who don't get it this is why there needs to be a good take up, its also why the childhood ailments are back, since when there was the vaccine scare a lot of parents did not get their children vaccinated and that gave the viruses time and space to spread.
Brian
Or alternatively, you have failed to grasp the concept of a double blind randomised trial.
It was one of the reasons the trials took longer than expected and had to be expanded to additional countries to maintain a large enough possibility of exposure.
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