Digging deep into the numbers behind the vaccines

Doctor with gloved hand holding syringe of vaccine

Theodore Roosevelt is generally credited with coining the famous phrase about effort and reward: “Nothing in the world is worth having or worth doing unless it means effort, pain [and] difficulty…”.

Given the seemingly never-ending effort, pain and difficulty surrounding the roll out of the Oxford AstraZeneca coronavirus vaccine, those involved could do worse than fall back on Roosevelt’s dictum.  Ever since the AstraZeneca vaccine was first announced to the world it has been dogged by bad luck, poor PR and political blunders.  Within days of the announcement of positive test results the vaccine’s overall efficacy came under attack, before being vindicated by further trials. Then European heads of state publicly questioned its ability to treat older people, before rowing back on the position too.  The latest set-back to hit the vaccine, and its roll out, concerns a relatively small number of individuals reporting blot clots after receiving the vaccine.

The data around ‘thrombotic events’ has neatly divided opinion.  On one side you have the UK, the European Medical Agency (EMA) and the World Health Organisation (WHO) who have all looked at the available data and said the vaccine remains safe to use.  On the side other are a number of largely European countries including Germany, Netherlands and Italy who have looked at exactly the same data and concluded the roll out of the vaccine should be suspended, at least temporarily.

This is confusing. That medical experts and / or political decision makers can look at the same set of data and come to diametrically opposing viewpoints is unhelpful to say the least.  Understanding why some of these decisions have been made may be impossible.  What we can do however is better understand the data and what it tells us about the vaccine.

The data was set out in the last few days in a statement by AstraZeneca as part of their ongoing job of monitoring the safety of its vaccine. The statement explains that the number of blood clots reported to date are minor, in fact lower than might have been expected in the general population.  The statement reads: “So far across the  EU and UK, there have been 15 events of DVT and 22 events of pulmonary embolism reported among those given the vaccine, based on the number of cases the Company has received as of 8 March. This is much lower than would be expected to occur naturally in a general population of this size…”.

Dig deeper into where some of this data comes from and you get to the Yellow Card system used in the UK to monitor all reports of adverse conditions that arise following medical treatments, such as vaccines.  Any and all reported conditions are logged in the system from something as benign as soreness around the injection wound to more serious matters such as blood clots.  What is important to stress, and this is made clear on the Government site, is that all conditions are logged whether or not the person making the report considers they may be linked to the medical treatment received.  This means that naturally occurring conditions get included in the data alongside those that are genuinely linked to the treatment.  No differentiation is made.  

What all the reporting around the data makes very clear however is that no causal link can be ascribed between the numbers of ADRs themselves and the side effects of any medicines.  This is data in its most raw form.  The purpose of the system is to flag up areas that for ongoing investigation and enquiries.  This is all part of the ongoing monitoring of medicines and medical instruments. Quite properly, this is exactly what the WHO and EMA are doing with all the various coronavirus vaccinations including the AstraZeneca version, while reiterating their guidance that it remains safe to take.

For more information on the work international authorities are doing in respect of the vaccination programmes you can go direct to their websites, the WHO here and EMA here.