Health Tips

Perhaps by now you’ve already known this: authorities in certain countries speculated that AstraZeneca's or Johson & Johnson’s COVID-19 vaccines are linked to a few rare but serious blood clotting cases. In this article, we bring you a simple explanation of the entire story so far, with the hope that the article brings better clarity to people who are hesitant to receive COVID-19 vaccine due to concerns of blood clot. 

Take note that at the time of writing this article, scientists worldwide are still investigating the blood clot cases associated with the two COVID-19 vaccines, information in this article might be outdated in the future.

What happened with the two vaccines?

It all started when the European regulators have reported more than 220 cases of unusual blood clots and low levels of platelets in patients who received the COVID-19 vaccine, called Vaxzevria, which was developed in the United Kingdom by AstraZeneca in Cambridge and the University of Oxford. Similar incidence was also reported in Australia.

Image via Fuzis, CC BY-SA 4.0 , via Wikimedia Commons

Meanwhile in the United States, six cases of a rare type of blood clot developing in people who received the Johnson & Johnson vaccine were reported in late March and early April to the US authorities. These happened amidst millions of doses administered to US citizens. Interestingly, all six people were women aged 18–48 years who experienced onset of symptoms between 6–13 (a median of nine) days. Sadly, one woman died. Medical authorities from various countries quickly jumped into investigation, which followed by temporary pause of these two vaccines usage. 

To be fair, when we said that these two vaccines are linked to rare but serious blood clotting cases, we don’t mean that the vaccines cause the blood clot; it’s just that these two vaccine and certain blood clot cases seemed to have some unclear connection, but it doesn’t imply causation. At this stage, scientists simply do not know enough to answer that. 

Introducing, vaccine-induced immune thrombotic thrombocytopenia (VITT)

However, scientists do come up with a convincing hypothesis: such blood clotting is a rare side effect called vaccine-induced immune thrombotic thrombocytopenia (VITT). Not only the name is mouthful to read, but it is a paradoxical medical condition.

VITT is a rare immune response towards the component in vaccines. It is thought that some people, for unknown reasons, received the vaccine and their immune response produces antibodies that destroy their own platelets and release a bunch of blood-clotting materials. Therefore, people with VITT would experience markedly reduced levels of platelets, which increases the risk of bleeding; but at the same time, somewhere else in the body, such as the brain or abdomen, unusual blood clots are formed, which blocked blood flow to these organs. 

(Fun fact: We’ve seen a similar medical condition called heparin-induced thrombocytopenia (HIT), which is a similar condition but in response to a medicine that prevents blood clot, known as heparin.)

Scientists also noticed that these blood clot cases are specific to vaccines that rely on adenovirus vectors to work, which are the technology used in AstraZeneca’s and Johnson & Johnson’s COVID-19 vaccines. Both use the adenovirus as the “delivery man” to carry the DNA encoding a coronavirus protein called spike into human cells, thereby stimulating our immune system to start churning out antibodies that can fight future COVID-19 infection. But at the present, scientists aren’t sure which component of these vaccines could be triggering VITT — it could be the adenovirus vector, the spike protein, or a contaminant present in the adenovirus vector. 

The benefits still outweighs the risks

At the point of writing, vaccination efforts using both AstraZeneca’s and Johnson & Johnson’s COVID-19 vaccines have been resumed in countries who paused them before. After a detailed and careful investigation into all blood clotting reports, various drug authorities concluded that these rare blood clotting cases happened amidst millions of doses administered. 

There are not many decisions we make in life that are free from risk, and many medicines do have their fair share of rare but serious side effects. With that being said, vaccines and medicines are products that have gone through rigorous safety evaluation in clinical trials, and if you’re in doubt, you can always consult a healthcare professional. But more importantly, the reason you should take a vaccine or a medicine when you need it is because, despite its possible side effects, not taking it may lead to even more suffering. COVID-19 infection increases the risk of blood clotting in the brain, known as cerebral venous thrombosis, or CVT. This is among many other health complications of the COVID-19 infection that can affect a person’s quality of life, or worse, lead to death. 

So, should you receive AstraZeneca's vaccines?

Although serious side effects are very rare on a population level (approximately one in a million), the risk may be higher or lower for an individual level. For example, current data suggests the risk of VITT might be higher than one in a 250,000 doses in a young woman. Of course, this doesn’t mean that young women should not receive AstraZeneca’s vaccine. Currently, the Covid-19 Vaccine Supply Access Guarantee Special Committee (JKJAVMY) is still deliberating on whether Malaysia should continue using AstraZeneca’s vaccines.

If you experience any of the following from around four days to four weeks after vaccination you should seek medical advice urgently.

• a new, severe headache which is not helped by usual painkillers or is getting worse

• a headache which seems worse when lying down or bending over

• an unusual headache that may be accompanied by:

  • blurred vision, nausea and vomiting

  • difficulty with your speech

  • weakness, drowsiness or seizures

• new, unexplained pinprick bruising or bleeding

• shortness of breath, chest pain

• leg swelling

• persistent abdominal pain

A word from Doc2Us

If you have any enquiries related to COVID-19 and its vaccines, you can consult our COVID-19 Task Force, which consists of professional doctors and healthcare professionals, for FREE! 

You can access to free COVID-19 virtual health advisory by downloading the Doc2Us app on http://onelink.to/doc2us or use our web chat https://web.doc2us.com/

For more information about COVID-19 vaccination programme in Malaysia, visit https://www.vaksincovid.gov.my/

Disclaimer: COVID-19 is a novel disease. The information and scientific evidence of its development and vaccines are changing as we speak. Some content of this article may be outdated in the future. We encourage you to always speak with a healthcare professional you trust for the latest updates on COVID-19 and its vaccines.

Read more:

Does the brand of COVID-19 vaccines matter?

https://www.doc2us.com/index.php/does-the-brand-of-covid-19-vaccines-matter

Should you receive Covid-19 vaccine if you have a drug allergy?

https://doc2us.com/should-you-receive-covid-19-vaccine-if-you-have-drug-allergy

Side effects of Covid-19 vaccine: should you be worried? https://doc2us.com/side-effects-of-covid-19-vaccine-should-you-worry

What you need to know about the COVID-19 vaccine

https://doc2us.com/the-star-of-year-2021-covid-19-vaccine

Should pregnant women take COVID-19 vaccine?

https://doc2us.com/covid-19-vaccines-pregnancy-and-fertility-in-women

References

1. WebMD - Scientists Find How AstraZeneca Vaccine Causes Clots

2. The Washington Post - Federal agencies lift pause on use of Johnson & Johnson vaccine, saying benefits outweigh risks

3. The Conversation - Is it the adenovirus vaccine technology, used by AstraZeneca and Johnson & Johnson, causing blood clots? There’s no evidence yet

4. The Conversation - What is thrombocytopenia, the rare blood condition possibly linked to the AstraZeneca vaccine?

5. Nature - COVID vaccines and blood clots: five key questions

6. BBC - Covid vaccines and blood clots: Your questions answered

7. Scientific American - Blood Clots and the Johnson & Johnson Vaccine: What We Know So Far

8. Yale Medicine - The Johnson & Johnson Vaccine and Blood Clots: What You Need to Know

9. CDC - Recommendation to Pause Use of Johnson & Johnson’s Janssen COVID-19 Vaccine

10. Toronto Star - Understanding the blood clot issue behind the AstraZeneca vaccine and its safety

Cover image credit: Fuzis, CC BY-SA 4.0 , via Wikimedia Commons

Written by

Ms Joyce Toh