Tuesday, July 27

There is no evidence that the Oxford vaccine causes blood clots. So why are people worried? | Vaccines and immunizations


Sstories about people blood clots shortly after taking the Oxford / AstraZeneca vaccine they have become a source of anxiety among European leaders. After a report of one death and three hospitalizations in Norway, which found serious blood clots in adults who had received the vaccine, Ireland temporarily suspended the jab. Some anxiety about a new vaccine is understandable and any suspected reaction should be investigated. But In today’s circumstances, we must think both slow and fast, and resist making causal links between events where neither can. exists.

As Ireland’s Deputy Chief Medical Officer Ronan Glynn has stressed, there is no evidence that this vaccine causes blood clots. It is a common human tendency to attribute a causal effect between different events, even when one is not present: we wash the car and the next day a bird is relieved all over the hood. Typical. Or, more seriously, someone is diagnosed with autism after receiving the MMR vaccine, so people assume a causal connection, even when there isn’t. And now, people develop blood clots after receiving a vaccine, raising concerns about whether the vaccine is what caused the blood clots.

Call it luck, chance or destiny; it is difficult to incorporate this into our thinking. So when the European Medicines Agency says there have been 30 “thromboembolic events” after around 5 million vaccinations, the crucial question is: how many would be expected anyway, in the normal course of things?

We can try a quick calculation on the back of the envelope. Deep vein thrombosis (DVT) occurs around one person for every 1000 every year, and probably more in the elderly population that is vaccinated. Working on the basis of these figures, out of every 5 million people who get vaccinated, we would expect significantly more than 5,000 DVTs a year, or at least 100 every week. Therefore, it is not surprising that there have been 30 reports.

It would be so much easier if we had a group of people exactly like those who are being vaccinated but who were not prodded. This would tell us how many serious events we could expect to happen to people that were the result of sheer bad luck. Fortunately, we have that group. In trials leading to the vaccines being approved in the UK, volunteers were randomly assigned to receive either the live vaccine or a dummy injection. Then they all reported on the damage they experienced, but more importantly, no one knew whether they had received the actual substance or an inert injection. By comparing the number of reports from the two groups, we can see how many “reactions” were actually due to the active ingredients and how many were related to the vaccination process or would have occurred anyway.

38% of those who received the real vaccine reported some kind of adverse events, but surprisingly 28% of those who received the dummy vaccine. also reported a side effect. This shows that the vaccination process itself causes about two-thirds of all reported harm. Of more than 24,000 participants, less than 1% reported a serious adverse event, and of these 168 people, slightly more had received the dummy vaccine than the active one. Therefore, there was no evidence of an increased risk from taking the AstraZeneca vaccine. the Pfizer trials had similar results, with milder or moderate adverse events in the vaccine group, but an almost identical number of serious events.

Trials are short and comparatively small, and they tend to include healthy people, so we must collect real-world data as vaccines are implemented. In the UK, adverse reactions are reported using the ‘yellow card’ system, which dates back to the days when doctors filled out yellow cards to report side effects. Until February 28, around 54,000 yellow cards They have been reported for the Oxford / AstraZeneca vaccine, out of around 10 million vaccinations administered (the Pfizer vaccine has a slightly lower rate). So for both vaccines, the overall reporting rate is around three to six reports per 1000 injections. That means a much higher number of side effects are reported in trials than through the yellow card system (of course, a factor in this underreporting may be the yellow card website, which seems designed for medical professionals rather than of patients experiencing side effects). ).

The vast majority of side effects reported through the yellow card system and in randomized trials. These are reports of direct reactions to the needle stick, such as arm pain, or flu-like subsequent symptoms, such as headache, tiredness, fever, etc., that disappear within a few days. The most serious problem is anaphylactic reactions, and advice You should not inject anyone with a previous history of allergic reactions to a previous dose of the vaccine or its ingredients.

So far, these vaccines have been shown to be remarkably safe. In fact, it is perhaps surprising that we haven’t heard more stories of adverse effects. There could well be some extremely rare event that is triggered by Covid-19 vaccines, but there are no signs of this yet. We can only hope that this message reaches those who still doubt due to the misinformation that has spread about the alleged harm of vaccines, and the useless comments made by some European politicians.

Will we ever be able to resist the urge to find causal relationships between different events? One way to do this would be to promote the scientific method and make sure everyone understands this basic principle. Testing a hypothesis helps us see which hunches or assumptions are correct and which are not. In this way, randomized trials have shown the effectiveness of some Covid treatments and have saved a large number of lives, while showing us that some exaggerated claims about Covid-19 treatments, such as hydroxychloroquine Y convalescent plasma, they were wrong.

But I don’t think we can fully rationalize from the basic and often creative urge to find patterns, even where they don’t exist. Perhaps we can expect some basic humility before claiming that we know why something has happened.


www.theguardian.com

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