Rare Vaccine Side Effects - Why it's so hard to InvestigateThem

[Jm954]

From Nature 1st April 2021

In mid-March, several European countries paused distribution of the COVID-19 vaccine made by the University of Oxford, UK, and the pharmaceutical firm AstraZeneca, following reports that some people had developed blood-clotting disorders after receiving the jab.

The decisions were based on a group of around 20 million vaccinated people in the United Kingdom and European Union, 25 of whom experienced serious blood clots associated with lowered platelet counts, resulting in 9 deaths. However, a review of the cases by the European Medicines Agency (EMA) could not say definitively whether the reported cases were linked to the AstraZeneca vaccine, and concluded that the benefits of the vaccine outweigh any risk. The countries have since resumed vaccinations, although Germany has stopped giving the vaccine to those under 60 after its own safety-monitoring systems reported 31 severe blood clots in a group of 2.7 million vaccinated people.

These events illustrate how fiendishly challenging it is to prove that a medical problem following immunization — known as an adverse event — was caused by the vaccine itself. Public-health officials must strike a “delicate balance” when communicating the risk of rare side effects alongside the dangers of severe COVID-19, says vaccinologist Kathryn Edwards at Vanderbilt University School of Medicine in Nashville, Tennessee. Physicians worry about fuelling anti-vaccine movements that are already increasing vaccine hesitancy in some communities. At the same time, it is important not to dismiss the potential for rare but severe side effects until researchers can establish causality, a process that can take years.

To investigate the link, researchers conduct studies to determine the rate of adverse events in vaccinated populations compared with the probability that they occur by chance in people who haven’t received the vaccine. They also need to determine the mechanism that could have caused the reaction.

Even the largest clinical trials are not designed to detect extremely rare side effects, which might occur in fewer than one case per 10,000 vaccinations. Because hundreds of millions of people are now being vaccinated against COVID-19, it makes sense that even very rare events — such as severe allergic reactions or blood clots — will start to appear in safety reports, Bastian says. The challenge now is to work out which of these events are actually linked to the vaccine.

Currently in the UK the advice is to get the covid vaccine as the benefits far outweigh the potential risks but, as always, it is best to discuss your own individual risk with your doctor.

More here: nature.com/articles/d41586-...

Jackie

[Psmithuk]

Thank you, Jackie. I understand the difficulties overall, but wonder about the low platelets associated with the blood clots. Do you/they think they were caused by the vaccine, as we might then be more at risk. I imagine this is unanswerable, but thought I’d pose it anyway!

Cx

[Jm954 Administrator in reply to Psmithuk]

Low platelets are usually associated with bleeds not clots and it's another of those situations where the cause and effect is unknowable, at least at the moment.Jackie

[Psmithuk in reply to Jm954]

Thank you, Jackie, I know it’s a bit early to expect any answers! It’s just another niggling thought to add to the others.Chrisx

[Peggy4]

I see on the news that it’s not to be given to under 30’s or certain blood conditions. Does that include us?

[Newdawn Administrator in reply to Peggy4]

This is the current Govt. advice Peggy. It seems to centre around people with thrombocytopenia (low platelet counts) though also others doctors may consider medically at risk (not specified why), are advised to have a different vaccine;

gov.uk/government/news/mhra...

This is taken from the Govt guidelines;

‘As a precaution, administration of COVID-19 Vaccine AstraZeneca in people of any age who are at higher risk of blood clots because of their medical condition should be considered only if benefits from the protection from COVID-19 infection outweighs potential risks.

Anyone who experienced cerebral or other major blood clots occurring with low levels of platelets after their first vaccine dose of COVID-19 Vaccine AstraZeneca should not have their second dose. Anyone who did not have these side effects should come forward for their second dose when invited.

Pregnancy predisposes to thrombosis, therefore women should discuss with their healthcare professional whether the benefits of having the vaccine outweigh the risks for them.

The MHRA recently confirmed that the evidence to date does not suggest that the COVID-19 Vaccine AstraZeneca causes venous thromboembolism without a low platelet count.’

Newdawn

[Peggy4 in reply to Newdawn]

Ah I see. Thanks Newdawn

[Kwenda in reply to Peggy4]

The problem appears to come after the FIRST dose, and then about 4 days afterwards.There have been NO diagnosis of blood clots after second doses according to the expert interviewed on the Today program.

So as long as the first dose was without signs of any clots the second dose should be safe.

Dick

AZ first dose, second dose booked for next week.

[Jm954 Administrator in reply to Peggy4]

Newdawn has explained it well but the reason is also the risk/benefit balance of clots v benefit from vaccine/risk of serious illness or dying. The risk of a clot in the under 30s is finely balanced against the risk of being sick from covid as both are extremely low. In the older age groups the balance is firmly in favour of the vaccination because there is a much greater risk of being seriously sick or dying from covid.

I hope I've explained it well enough.

Jackie

[Peggy4 in reply to Jm954]

Thank you. I had the Pfizer months ago but some of my children fall into this age bracket.Peggy

[Jm954 Administrator in reply to Peggy4]

They will get the Pfizer one Peggy now that it's definite guidance.