Does Pfizer have a blood clot risk? Latest advice for the Covid vaccine


    The Pfizer Covid vaccine may cause side effects, although not everybody gets them. Experts advise the most common side effects are pain at the injection site, tiredness, headache, muscle pain, chills, joint pain and fever, but that most side effects are mild or moderate and go away within a few days of appearing. But is the Pfizer vaccine associated with a risk of blood clots like the AstraZeneca jab?  

    According to the UK government’s latest advice, blood clots, specifically vaccine-induced thrombosis and thrombocytopenia (VITT), have not been associated with the Pfizer vaccine.

    In April, concerns started to emerge in Australia about the Pfizer vaccine’s association with blood clots.

    A 40-year-old police sergeant from Brisbane made headlines after developing a blood clot three days after receiving the vaccine.

    But a statement released by Queensland police revealed the man, who works in the state’s hotel quarantine system, returned to duty and had a history of clotting.

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    VITT was found to be a very rare adverse event characterised by presence of blood clots with low levels of platelets following vaccination with the AstraZeneca vaccine.

    Between 9 December 2020 and 5 May 2021 there were more than 160 cases of VITT out of a total of 30.8 million doses of the AstraZeneca vaccine administered in the UK.

    But UK Parliament has stated: “The overall risk of VITT following a dose of the University of Oxford/AstraZeneca vaccine is 10.9 per million doses.

    “This varies according to age groups and it is estimated to be around 1 in 100,000 for people over 50 and 1 in 50,000 for people aged between 18 and 49 years.


    “Following an age-based risk-benefit analysis, the Joint Committee on Vaccination and Immunisation (JCVI) concluded that people aged under 40 should be offered an alternative to the University of Oxford/AstraZeneca COVID-19 vaccine.”

    Like the Pfizer vaccine, the Moderna vaccine, which is also currently deployed in the UK, hasn’t been associated with VITT.

    VITT cases have been reported following vaccination with the Johnson & Johnson vaccine – a vaccine which uses the same technology as the AstraZeneca one.

    But this vaccine has yet to be approved for use in the UK.

    The UK government advises: “Some people have reported a sudden feeling of cold with shivering/shaking accompanied by a rise in temperature, possibly with sweating, headache (including migraine-like headaches), nausea, muscle aches and feeling unwell, starting within a day of having the vaccine and usually lasting for a day or two.

    “If your fever is high and lasts longer than three days, or you have other persistent symptoms, this might not be due to side effects of the vaccine and you should seek appropriate medical advice according to your symptoms.”

    If you get any side effects you should talk to your doctor, pharmacist or nurse.

    If you’re concerned about a side-effect it can be reported directly via the Coronavirus Yellow Card reporting site or search for MHRA Yellow Card in Google Play.

    Don’t report the same side effects to both systems to avoid dual reporting.

    Although serious side effects are very rare, if you experience any of the following from around 4 days to 4 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 or persistent abdominal pain


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