Consultant Haematologist at Oxford University Hospitals in the U.K. I'm here to share what you need to know on COVID-19 and thrombosis, including vaccine updates, pediatric considerations, and more.

Not so much a question as a comment. I’m a vascular surgeon and involved in thrombosis care in my country. I am so frustrated with the public jumping on any anecdotal report of thrombi secondary to vaccination - usually with no proof at all - and using it as an excuse as to why they won’t vaccinate. Lord knows I’ve pulled enough clots out of arteries in the last two years curtesy of COVID.

You've raised an important point. Covid-19 infection is itself strongly associated with blood clots. The blood clots seen after the adeno-viral vector vaccines are extremely rare and this should not deter people from having the vaccine to protect them against covid-19 infection. If symptoms such as headache or abdominal pain start 5 to 30 days after an adeno-viral vector vaccine, a blood count can be checked to ensure the platelet count is normal. Keep up the great work you are doing!

I caught covid at 36 weeks pregnant and was given clexane to prevent blood clots. It's now 5 months later, is my risk of developing blood clots due to covid completely gone?

Ftr I'm no longer on clexane, that stopped shortly after birth.

You are right to ask this. The risk of blood clots after Covid-19 infection has been found to persist for up to 6 months but it does get less over time. Women are generally at increased risk of thrombosis in pregnancy, particularly in the 6 weeks after delivery. So I think your higher risk period would be over now, but it is always important to keep mobile, hydrated and do regular gentle exercises.

Hi Dr. Pavord. My question doesn’t pertain to thrombosis, but wanted to ask just in case. As a hematologist, I’m wondering if you’ve noticed an uptick of Aplastic Anemia cases since the beginning of COVID?

Thank you for doing this AMA.

Aplastic anaemia is when your body stops producing enough new red blood cells. It can often be caused by immune disease and Covid-19 is known to cause strong immunological reactions, which is why your question is very sensible. However there has not been an increase in cases of aplastic anaemia over and above the normal background population rates, during the pandemic.

For cases of mild covid where you may never see a doctor, how concerned should you be about blood clots? Any warning signs to be aware of? Thanks!

The risk of blood clots is greatest in those who are hospitalised or who have severe infection, however blood clots have been seen in individuals with mild Covid-19 infection. Typical signs of blood clotting are pain and swelling in one leg, or sharp chest pain on deep inspiration. It is important to keep mobile and hydrated to help prevent blood clots.

I've had two family members experience Covid-induced clots, and I'm curious if there has been any study of the prophylactic use of blood thinners on Covid patients? I'm doubly curious as I have a history of unprovoked DVT and am on blood thinners for life. (I've so far escaped Covid and have all my shots, including the new bivalent booster - and no, none of us have Factor V Leiden or any other genetic clotting markers.)

Thanks for this question. There have been many studies on use of prophylactic blood thinners in Covid-19 patients. There is good evidence for their benefit in patients admitted to hospital. The dose and duration is assessed on a case-by-case basis depending on the balance of bleeding and clotting risk factors. Severe covid-19 also increases bleeding risk so this needs to be balanced carefully.

I've had a blood clot before, is it safe for me to have a covid-19 vaccination?

Yes it is safe for you to have a vaccine even if you have had a blood clot before. The blood clots seen after vaccine are extremely rare and result from an immune reaction to the vaccine. People with pre-existing risks of blood clots or previous blood clots are no more at risk of getting this immune reaction. We are not seeing these immune reactions in the UK anymore

I have heard a lot about Vaccine-inducted thrombotic thrombocytopenia (VITT) - what is it and how common it? What should I do if I suspect I have it?

VITT is a very rare immunological reaction to the Covid-19 vaccines which use an adenoviral vector. Symptoms start 5 or more days after vaccination, usually with headache or abdominal pain. Symptoms starting before 5 days are common and are not VITT.

I've had all the recommended vaccines and I am also on birth control; I realize that I am at a higher risk for blood clots - even at a young age - what can I do to be proactive and make sure that I am preventing clots?

Everyone has a small risk of blood clots, and the birth control pill (combined contraceptive pill) increases this risk. The risk associated with the pill are highest in the first 3-6 months and are less significant after 12 months. It is important to keep mobile and hydrated to reduce the risk of blood clots.

Is it likely that Covid will get more mild as it develops? I've had it twice, the original and the Beta version. Are there very long term health issues to wrry about in later life or is that not clear yet?

Thanks for your service.

The more recent strains of COVID are more mild but it may still cause serious disease particularly in those who are immunosuppressed, so it is important that people continue to have their vaccinations as they are offered. We don't think there will be long term health issues in people who have made a good recovery from COVID-19 infection but we only have two years of follow up information so far.

Why is COVID-19 not commonly understood to be a vascular disease, even in the face of mild respiratory issues?

Thank you for this question, Covid-19 is well known to be associated with injury to the blood vessels causing an increased risk of blood clotting as well as bleeding.

I see you are from the UK. What is the state of COVID-19 there right now? Are cases on the rise or slowing down?

At the moment, cases are slowing down, but we may experience another surge expected as we come into winter. I would encourage to have their autumn COVID-19 booster at this time.

What is your biggest challenge in seeing COVID-19 patients? How do you compartmentalize that difficult work, especially with some patients may not survive?

Thank you for this thoughtful question. It can be emotionally draining at times. The biggest challenge to me was VITT (vaccine -induced thrombocytopenia and thrombosis). Although this was rare, it affected previously fit and well young adults who presented with multiple blood clots and organ damage. I am a mother of three children in their 20s so I empathised with the pain these families were going through. As soon as we were aware of these patients, we formed the UK Expert Haematology Panel and worked all our spare hours to quickly understand the condition and agree on best management. We managed to improve outcomes and prevent further cases.

One more question: Is there any new research coming out about the link to COVID and blood clots? I have been seeing more stuff on the news about it.

There is a lot of research into the link between Covid-19 infection and blood clots. The best research is with clinical trials and I would encourage all individuals with covid-19 infection to take part in a clinical trial, so that we can understand more about this area.

Have you seen patients who developed ITP after getting the Pfizer vaccine? Starting around 3+ months after the booster and lingering for months or more after?

No we haven't seen this. A very large study was conducted in Scotland and showed no increase in ITP after the Pfizer vaccine. In the case you describe, it would be more likely that the ITP occurred by chance rather than caused by the vaccine. We are looking at all ITP cases in the UK occurring within 30 days of vaccine.

Thanks so much for the reply! Is this the one you are referring to?

https://www.ed.ac.uk/news/2021/covid-vaccine-linked-to-low-platelet-count

Yes, thank you for this news link

If I'm pregnant, do I have a higher risk of getting COVID? Do you recommend that I get the vaccine? I live in the U.S.

I strongly recommend you to have the vaccine if you are pregnant or trying to get pregnant. It is safe to have at any stage of pregnancy. You are no more at risk of getting Covid-19 if you are pregnant but without the vaccine you are more at risk of an infection becoming severe and causing an early birth.

Haha well spotted! it should be COVID, I write it so often I have got into bad habits!

Have you seen any type of issues regarding COVID 19 and people with hemochromatosis?

No I have not seen this specifically, although any comorbidity can potentially complicate or affect recovery from covid-19 infection. It is important that the haemochromatosis is monitored and controlled.

Hi! My partner had Pulmonary embolisms last year after getting the 3rd vaccine & mild COVID at the same time. There is family history of strokes. Is she at increased risk of vaccine complications, as she is being called for booster, or is it more likely to have been a response to COVID? She is still on Apixaban awaiting haematology investigating antiphospholipid syndrome, would that mitigate risk?

It is unlikely that the vaccine caused the blood clot. It may have been due to the combination of antiphospholipid syndrome and Covid-19 infection. I would recommend that your wife has the autumn booster, she is no more at risk of vaccine complications than others and she would be more at risk of further blood clots if she had covid infection again. Hope that helps to reassure you.

Why do you think some people are so hesitant about vaccines? What do you recommend to your patients?

I recommend to my patients that they are vaccinated in line with the national programme. In the UK we are administering the autumn boosters right now. The benefits of the vaccine in protecting against severe Covid-19 infection and hospitalisation far outweigh the risks, particularly in middle-aged and older individuals.

I am interested in getting involved in World Thrombosis Day, how can I do that?

Great question. World Thrombosis Day is in just a couple weeks on October 13. The campaign is hosting a variety of activities online including a Twitter Roundtable, Facebook Live broadcast, and more. You can also get involved in your local community by visiting the partner map on their website. Visit https://www.worldthrombosisday.org/ to see all the activities and ways to get involved.