10th April 2021, Dr Chee L Khoo
It’s as if the government hasn’t made the roll out messy enough. With the bombshell of the clot issue clouding the whole AstraZeneca covid-19 vaccine, all of you will be utterly confused. The public statements issued by the government or the medical experts, in my opinion, doesn’t actually help. The conflicting posturing by different arms of the government just serves to add to the confusion. I am sure many of you are not sure whether to even go ahead with the vaccine at all. The new developments haven’t really changed the recommendations that much. I have kept most of you up to date with developments over the last few months ahead of this mess. As usual, let us cut through the chase by looking at it objectively.
Clots and AZ vaccine – is there a connection?
The medical evidence is naturally still in the early days. It all started when Austrian medical authorities reported two cases of a very rare clotting disorder, heparin induced thrombosis (HIT). Heparin is an injectable drug we used to thin the blood (anti-coagulant). It is routinely used around the time of surgery to prevent clot formation during and after an operation.
In very rare occasions, in some people, instead of thinning the blood, heparin causes more clot formation. In these people, heparin activates the platelets, which are cells used in clot formation. More clots are formed by heparin instead of less. The activated platelets are destroyed leading to reduction in their numbers (thrombocytopenia). This paradoxically, make these patients more likely to bleed as well as more likely to form clots.
When HIT occurs, unless it is recognised early, it is common to increase heparin because there are more clots we need to dissolve. This obviously make the clotting worse. This occurred in the original two Austrian patients which lead to extension of more clots and yet more internal bleeding. Unfortunately, one of them died while the other is still in ICU.
As of 30th March, there have been reports of at least 31 cases from other European countries out of 5 million doses of AZ vaccine administered.
The clots are not your usual DVTs (clots in the calf) or pulmonary embolism (clots that goes to the lung) but are very rare clots in the veins of the brain (cerebral venous sinus thrombosis), abdominal vein (mesenteric) clots etc. Clots in these areas are extremely rare and typically occur in patients with clotting or platelet disorders.
Now, these patients with these rare clots after AZ vaccine occur within 5-20 days of the vaccine suggesting something similar to the HIT syndrome related to heparin injection but they have not had heparin prior to the vaccine.
So, why is this happening? We don’t know. It may be to do with the vaccine material, the adenovirus that carries the AZ vaccine or totally coincidental. There is evidence that the platelets are being activated by something but we don’t know by what. It’s still work-in-progress as we monitor the vaccine closely.
We also don’t know who are at more risk than others. Almost all the people who developed these unusual clots are under 30 years old and 8 out of 10 were women. As we uncover more clots here and overseas, we may be have more information which can guide us as to who is more at risk than others. We will also have more information about how to more effectively treat these clots and reduce the mortality rate relating to the clots.
What is the overall risk?
To date, there have been 31 cases reported out of 5 million doses. This equates to 1 case per 250, 000 vaccines administered. Unfortunately, mortality is 25% of those that developed vaccine related HIT. We don’t know whether early recognition of the syndrome and using other blood thinners instead of heparin would reduce the mortality rate. Other agents have been successfully used in HIT to reduce the activation of the platelets to end the vicious cycle of blood clotting and blood thinning.
Putting everything into perspective
The risk of dying if you get Cvoid-19 infection is about 3 out of 100. It is higher for older people and people with co-exisiting medical conditions including diabetes and hypertension. The risk of developing HIT with the AZ vaccine is 1 in 250,000 vaccines administer with the risk of dying being 1 in 1 million vaccine administered.
Whether you should have the vaccine or not then is a balance between your risk of getting severe disease if you contract Covid-19 infection and your risk of getting the rare side effects of clotting. It is still generally advisable for those in Phase 1A and Phase 1A to have the AZ vaccine.
Phase 1A
These are people at the frontline and the risk of contracting the disease is higher than the general population in Australia.
Over 50 years old
The risk of getting severe disease (including death) if you get Covid-19 infection is higher. The risk of getting clots is lower than 1:250,000. We recommend that you have the vaccine as the benefits easily outweigh the risks.
Under 50 years old
The risk of getting the clots is higher if you are under 50 years old but the risk is still very low at 1 in 250,000 vaccines administered. The risk of getting Covid-19 infection depends on your individual circumstances. Some of you may choose to go ahead with vaccine while others may prefer to wait. Overall, if you choose to have the vaccine, the risk of getting clots remains very low at 1 in 250,000 vaccines administered.
Phase 1B
Over 50 years old
The risk of getting severe disease (including death) if you get Covid-19 infection is higher. The risk of getting clots is lower than 1:250,000. We recommend that you have the vaccine as the benefits easily outweigh the risks.
Under 50 years old
To qualify for Phase 1B, you would have a significant medical condition that will put you at significant risk of developing severe disease is high. Compared with the rare risk of developing clots with the AZ vaccine, you should have the vaccine as the benefit easily outweigh the risk.
Dr Khoo’s recommendations
If you are over 50 years old, I do recommend that you go ahead and have the AZ covid-19 vaccine when we have them available.
If you are over 50 years old and have a significant medial illness (including diabetes, hypertension, on chemotherapy, recent cancers), you definitely should have the AZ covid-19 vaccine when we have them available.
If you are under 50 years old and you are in Phase 1A, you should have the covid-19 injection when we have them available.
If you are under 50 years old and you are in Phase 1B, you too should have the Covid-19 injection when we have them available.
If you are under 50 years old and you are not in Phase 1A nor Phase 1B, then your vaccination is not due till mid to end of May 2021. Let’s come to that when we come to that.