As of today in excess of 350 million vaccine doses have been given around the world. For those who have received the vaccine, there have been no deaths or hospitalisations due to COVID.

This is an extraordinary result and credit to the outstanding scientists who are doing this work. As with any medication, there can be a hunch that there is a side effect. These hunches are important to follow up and the way drugs are regulated, especially in Australia with our TGA, they are.

There has been a hunch that of the people who received the AZ vaccine, a few subsequently developed blood clots either as a DVT [deep vein thrombosis] or in their lungs. At this stage, there is no evidence at all that these are associated with being vaccinated. To stop a vaccination based on a hunch will lead to an increase in COVID deaths.

So far, data from the phase 3 clinical trials and real-world rollouts suggest blood clots and other “thromboembolic” events occur no more frequently in people vaccinated with the AstraZeneca shot than they do in the general population. Thromboembolic events include blood clots, pulmonary embolisms and deep vein thrombosis.

As vaccine safety experts, we agree it’s very important to investigate these safety concerns thoroughly.

But we would urge extreme caution in pausing rollouts while investigations are underway, because once a vaccine rollout is paused, it can sometimes dent vaccine confidence so much that it struggles to recover, as seen in Japan with the Human Papillomavirus vaccine.

In my opinion, this response is an overreaction and while this is perhaps how these countries prefer to respond we should make sure we don’t overreact in our country and that we continue to make evidence-based decisions based on the available data at hand.

This vaccine has proven very safe and effective in large clinical trials. In fact in clinical trials now exceeding 60 000 participants some of these events were observed in low numbers but there were actually fewer in the vaccinated group than in those that had not received the vaccine

Available data from the use of this vaccine in the EU and UK now includes more than 17 million people vaccinated and has revealed only 15 events of DVT [deep vein thrombosis] and 22 events of PE [pulmonary embolism]. This is much lower than would be expected in a population of this size and is similar to other COVID-19 vaccines.

What we know is that significant medical events such as these do occur and will keep occurring. Given we are now rolling out a vaccine globally in a short timeframe, by sheer chance some of these events will now occur in people who have been relatively recently vaccinated, however this relationship is coincidental, not causal. If this were not simply a coincidence we would have expected to see this occur in the clinical trials given their size and we would also expect the rates of these events to have increased in parallel with the roll-out of the vaccine, neither of these has occurred.

On the other hand, we do know that thrombotic events such as those reported here are recognised to have a higher incidence in patients with covid, both severe disease particularly in ICU and non-severe patients for example those hospitalised with neurovascular disease.

It has been reassuring to see large organisations such as the WHO and MHRA also continue to recommend this vaccine given predominantly that in their summation, the number of events reported after having the vaccine is not greater than the number that would have occurred naturally in the vaccinated population. Our own regulator, the TGA, has released a statement outlining that they too believe the link with the receipt of the vaccine and these events has not been confirmed yet they are continuing to closely monitor, as they do with all such events. It would clearly not be in anyone’s interest to recommend a vaccine in which they were not genuinely completely confident in its safety whether that be the manufacturer or relevant regulators.

The transparent and timely reporting of these events is extremely useful as it ensures that any potential adverse events can be accurately captured and their relatedness to receipt of the vaccine ascertained so that if there was a safety concern, it could be acted upon swiftly. In this case, we have enough data to demonstrate that these events have not occurred in a higher number of vaccinated individuals and it is therefore nothing more than a coincidence, hence we should continue to use this vaccine.

Australia has an excellent system through the TGA and National Centre for Immunisation Research and Surveillance (NCIRS) for the active surveillance of rare events that may occur after vaccination - the issue of blood clots appearing to occur after use of the AstraZeneca covid vaccine is being taken very seriously and is being carefully investigated. The data collected so far suggests that blood clots are not occurring any more often than would be expected by coincidence. The incidence and exact nature of the observed blood clots is under particular review in the UK where many millions have been vaccinated with the Oxford vaccine without a signal of concern emerging.