[id2000 (OP)]

A couple of weeks ago a friend in previously good health had a stroke caused by a blood clot in the brain. It occurred a couple of weeks after receiving the Oxford vaccine. Another friend suggested a connection but the rest of us felt sure it was a coincidence. However, it has caused me to take a particular interest in the recent reports coming out of Norway about blood clots in the brain following vaccination.

It is reassuring that AstraZeneca claim they have not seen abnormal levels of clotting amongst vaccine recipients but I am wondering how the so called 'yellow card' system for reporting possible adverse events works. Would a clinician automatically make a yellow card report for a stroke or clotting event that occurs shortly after vaccination or would they make their own judgement whether it was likely to be coincidence? It seems to me that if clinicians do not report all such events then evidence of any problem is going to be hidden by under reporting.

[alancalverd]

The yellow card system seems to be well supportedbut as with any postmarket surveillance of a generally sound pharmaceutical, you are looking for the recurrence of undefined and possibly unrelated needles in a very large haystack.

Part of the problem is the word "after". I developed arthritis after receiving the Salk polio vaccine. But most of my cohort have some degree of arthritis and 60 years is a long time "after", so it would be difficult to justify an allegation of causality.  You can expect adverse reactions that occur within a week of any treatment to be quickly notified and investigated, but a month later the link becomes rather tenuous in the patient's mind and even a thorough diagnosis at postmortem is unlikely to trigger an investigation of the patient's recent history unless there is a significant local outbreak of something really unusual - full credit to Dr Li Wenliang for identifying COVID, given that he was an ophtlamologist, not a respiratory physician!

The problem also has a converse. If you vaccinate the oldest 30% of the population, you can expect a fair number to die within say a year of treatment, mostly of fairly common conditions.  Differentiating between random clusters (and there will always be clusters in a random distribution)  and actual correlated effects is difficult enough, and if someone identifies and publishes a cluster that appears to be correlated  with treatment, it is almost certain that others will be alerted to the possibility and begin filing yellow card reports on incidents that would have passed without comment previously, or would have been ignored in the death certificate in the presence of some other causative factor, so the natural occurrence rate is almost certainly underreported

[evan_au]

Would a clinician automatically make a yellow card report for a stroke or clotting event that occurs shortly after vaccination

The problem is that a clinician would definitely not make a yellow card report for a stroke or clotting event that occurs before vaccination.
- So this system can alert you to potential problems, but can't tell you that it is a problem.

It seems to me that if clinicians do not report all such events then evidence of any problem is going to be hidden by under reporting.

I heard some statistics that:
- About 8% of people will suffer a life-threatening clot in their lifetime, without a vaccine.
        - This is a very high background rate, so it is inevitable that some people will have a life-threatening clot within a week of receiving the vaccine.
        - It takes a country with a well-integrated computerized national medical system to even be able to ask "Was the number of clots in the week after COVID vaccination greater, less or equal to the number in the week before vaccination?"
        - Norway has such a computer system, and at present, they are saying 'equal' (within the statistical limits of a finite sample population)

Even if all of the clots reported are due to the vaccine (very unlikely), that apparently works out at about 3 deaths per million people vaccinated in the UK.
- At the moment, in UK, the death rate from COVID-19 works out an order of magnitude higher, at around 43 deaths per million people, every week.
- Since the vaccine reduces the chance of COVID-19 death by over 90% (when fully vaccinated), you can actually reduce the death rate by vaccinating everyone.
- I will get vaccinated as soon as I am eligible for it

It may be a different story in a country like Australia, where the virus is under control, and the death rate from COVID-19 is 1 every few weeks. Taking the very high figure, vaccinating everyone over the next 6 months could cause the deaths of around 8 people.
- Meanwhile, the death rates from heart disease and cancer will continue at a high rate, totally masking the vaccination deaths.

There are researchers investigating whether the vaccine can affect people who have antibodies against platelets.
- COVID-19 infection definitely causes problems with clots in some people.

Listen from 8:55 for 2 minutes: https://www.abc.net.au/radio/programs/coronacast/heres-what-we-know-about-the-blood-clots-reports/13254096