Denmark, Austria, Iceland and Norway have stopped using the COVID 19 AstraZeneca vaccine because of some cases of thrombosis in vaccine receivers. On the other hand, the European Medicines Agency (EMA) has stated that there is no connection between the cases of blood clots, and the vaccine has been approved based on population and other scientific studies.

Based on the molecular pathogenesis of the COVID 19 virus, expression of viral Nucleoprotein is responsible for stimulation of “lectin pathway” and “pro-inflammatory cytokines reactions”. https://www.immunology.ox.ac.uk/covid-19/covid-19-immunology-literature-reviews/highly-pathogenic-coronavirus-n-protein-aggravates-lung-injury-by-masp-2-mediated-complement-over-activation

These two pathways are mostly responsible for the stimulation of interleukin 6 and the formation of micro thrombus in COVID 19 patients. https://www.frontiersin.org/articles/10.3389/fimmu.2020.01606/full

The AstraZeneca vaccine is based on expression of the Spike protein of the COVID 19 virus in Chimpanzee Adenovirus vector. In this viral vector vaccine, the viral Nucleoprotein that is responsible for thrombosis formation in COVID 19 cases doesn’t exist, and no pro-inflammatory reactions due to nucleoprotein have been observed due to AstraZeneca vaccination. The vaccine vector which is Chimpanzee Adenovirus doesn’t amplify in human cells and doesn’t have nucleoprotein similar to the COVID 19.

Considering these two scientific facts plus more epidemiological studies, the European Medicines Agency (EMA) made a scientific statement that no correlation exists between the AstraZeneca vaccine and the blood clots.

Vaccine safety is important. This issue is now being carefully examined by the European Medical Agency’s safety committee. https://www.ema.europa.eu/en/news/covid-19-vaccine-astrazeneca-prac-preliminary-view-suggests-no-specific-issue-batch-used-austria

Our Australian regulator and vaccine safety experts are keeping a close eye on the outcomes of the rapid review. At this stage it appears that the blood clots may have occurred in these people anyway and that the vaccine did not cause them, but investigations will continue. Regulators look at things like biological plausibility, evidence from the trials, what is happening in other countries, and background rates to see if there is an unexpected rise in blood clot events.

So far, the EMA note that 'As of 9 March 2021, 22 cases of thromboembolic events had been reported among the 3 million people vaccinated with COVID-19 Vaccine AstraZeneca in the European Economic Area.' The EMA state that this is not higher than in the general population. 

Countries around the world have set up systems to monitor for what are known as 'adverse events following immunisation'. WHO defines this as, 'Any untoward medical event that follows immunization and that does not necessarily have a causal relationship with the usage of the vaccine.'

Once an adverse event is detected, regulators and vaccine safety experts will investigate whether the event is thought to be caused by the vaccine or not. This is a normal part of any vaccine program. It demonstrates a system is open, transparent and responsive. Governments want to ensure they are giving people safe vaccines. 

Some countries will be extremely cautious and pause the vaccine program while they investigate. Others will still investigate but keep the vaccine program going. This may reflect how much the decision makers in a country tolerate temporary uncertainty about vaccine safety and balance that against the vaccine’s undoubted benefits of protection from COVID-19.

These are the dilemmas that leaders face when vaccine safety events occur. When vaccines are suspended due to such events, it can take a while for public confidence to return, even if the problem is later found to be unrelated. So these are never easy decisions.

The countries that have suspended the use of the AstraZeneca vaccine have acted with extreme caution by suspending vaccination, until such time as the risk can be assessed.

Blood clots are extremely common. For example, the CDC in the US reports 60-100,000 deaths per year from lung blood clots. These are more common again in the elderly and those with chronic disease who are the people who are the target of the early vaccination programs.

We also need to keep any risk in perspective. So far more than 2.5M people have died of COVID 19 and 8,000 to 10,000 people are dying each day around the world. More than 320 million people worldwide have already been vaccinated. More than 11 m people in the UK alone have been vaccinated with the AstraZeneca vaccine.

The scientifically conducted clinical trials of the vaccines prior to their approval did not identify any increased risks associated with the vaccine. The scientific community has not had the time to test these new vaccines over prolonged periods and in large populations but on the present knowledge there is no evidence of significant increased risk.

The seriousness of the disease we are trying to control means that we need to move quickly to roll out the vaccines to save lives and to restore social and economic activity. If the disease were to get out of control in Australia as it did in much of Europe and the USA, then we can expect between 30,000 and 40,000 people to die in Australia.