By Dr. Ross Walker
May 2021

The major medical news story over the past few weeks has been the potential risk of clotting associated with the Astrazeneca vaccine for COVID-19.

To date, around 25 million people around the world have been vaccinated with the Astrazeneca vaccine. The total number of vaccines for COVID-19 globally being 734 million with 159 million people fully vaccinated. The majority of these being in the United States using either the Pfizer or Moderna vaccines in most cases.

Over the past couple of months there have been a number of reports of blood clotting events within two weeks of vaccination with the Astrazeneca vaccine. These very unfortunate cases still need to be put in to perspective.

It appears that the clotting risk from the Astrazeneca vaccine is one in 200,000 and the death risk is one in 800,000. Every year, in Australia alone, 30,000 people develop blood clots unrelated to any form of vaccination. Of these, around 6% will die, especially if the clots are not detected early.

If a person sits on a plane from Sydney to Heathrow and develops the economy syndrome (i.e. deep venous thrombosis or DVT) they want to sue Qantas, but in fact they should be suing their relatives for giving them the clotting abnormality that predisposed them to this event. There are eight relatively common clotting abnormalities that predispose to DVT and pulmonary embolus, none of which are related to the potential vaccine induced clotting issue.

The two types of clotting abnormalities possibly associated with vaccination include, potential vaccine induced thrombocytopenia and cerebral venous sinus thrombosis.

A 44-year-old male in Melbourne developed probable vaccine induced thrombocytopenia recently around a week after receiving the vaccine. He was then treated in a Melbourne hospital. Thrombocytopenia is a condition that involves the platelets which are these sticky cells in the bloodstream that combine with clotting factors to form clots. If you cut yourself and start bleeding, it is necessary to form a clot to stop the bleeding. This is where the clotting factors and platelets perform their duties appropriately.

In potential vaccine induced thrombocytopenia, the platelet levels markedly drop below normal, which is where you would expect bleeding not clotting, but the platelets become incredibly sticky and inappropriately form clots that may then lead to clotting in different sites throughout the body and a severe syndrome which in a proportion of cases may even lead to death if not detected and treated early.

In cerebral venous sinus thrombosis, these form abnormal clots occurring in the veins that drain blood from the brain and are more common in pregnant women or those on the oral contraceptive pill; still an extremely rare condition.

The general risk of deep venous thrombosis or DVT in pregnant women is 10 times higher than normal and in those taking the oral contraceptive pill the risk is three times higher than normal. I would suggest, however, that women who develop these conditions in pregnancy or associated with the oral contraceptive pill have one of the more common clotting disorders such as Factor V Leiden, anti-cardiolipin antibodies or some other very uncommon disorder that makes your blood stickier than a person without these abnormalities. There is no relation to increasing clotting risk in these more common conditions & being vaccinated.

There are three vitally important points to make here:

1. Most importantly is the risk of contracting COVID-19 compared to the risk of side effects from the vaccination. In Australia alone, we have just over 900 deaths in around 30,000 COVID cases and when you look at the overall Australian population this is one death per 30,000 people. In the United States there has been half a million deaths from COVID-19 which equates to one death per 600 people.
2. The risk of dying from either of the above rare clotting conditions related to vaccination is one in 800,000.
3. The general risk of blood clotting per year in Australia equates to around 30,000 people with an associated 6% death risk, with no relation to vaccination, but purely because of the variety of genetic or auto-immune blood clotting abnormalities. These are relatively common but often poorly recognised problems and without treatment can lead to death or significant disability. But, with early diagnosis & management, we have highly effective therapies.

Thus, looking at the numbers, there is much less clotting risk in vaccinated people compared with those in the general public. It is my opinion that the government is being very cautious in suggesting that people under the age of 50 should not be vaccinated with the Astrazeneca vaccine but rather have the Pfizer vaccine. These rare blood clotting disorders associated with vaccination appear to be more common in people below the age of 50.

The bottom line is that whether it is the Pfizer vaccine or the Astrazeneca vaccine, these vaccines are incredibly safe and no one around the world who has been vaccinated with any vaccine that has been approved for use has developed severe COVID or died from a COVID infection.

The strong message here is that we all need to be vaccinated as soon as possible when we qualify. The frustration in this country is the slow rollout but the good news is that there are almost no cases of COVID-19 in our country so we can afford to wait. I will certainly be having my vaccination (almost certainly with the Astrazeneca vaccine) as soon as it is available. I would suggest you do the same.