The manufacturers of Vaxzevria, the Covid-19 AstraZeneca vaccine, have issued updated safety advice on the risk of thrombosis in combination with thrombocytopenia.
In a notice to healthcare professionals on 2 June, AstraZeneca advised that individuals diagnosed with thrombocytopenia within three weeks of vaccination with Vaxzevria should be “actively investigated for signs of thrombosis”.
“Similarly, individuals who present with thrombosis within three weeks of vaccination should be evaluated for thrombocytopenia.”
The notice outlined that the vaccine is contraindicated in individuals who have experienced thrombosis with Thrombocytopenia Syndrome (TTS) following vaccination with Vaxzevria.
“TTS requires specialised clinical management. Healthcare professionals should consult applicable guidance and/or consult specialists (e.g., haematologists, specialists in coagulation) to diagnose and treat this condition.”
Use of Vaxzevria was temporarily suspended here for a short time amid concerns about rare but serious blood clotting events.
The suspension was later lifted with advice that it be given to the over 60s only. Current advice from the National Immunisation Advisory Committee (NIAC) states that: “mRNA vaccines are preferable for those aged under 50 years including those with medical conditions with very high or high risk of severe Covid-19 disease”.
The European Medicines Agency (EMA) estimates that TTS occurs in 1/100,000 people vaccinated with Vaxzevria.
According to NIAC, Preliminary UK evidence suggests that the risk of TTS may not be higher and is possibly substantially lower (1.6/ million) after a second dose of Vaxzevria.
“Although most cases have been reported in females, this may be because more women have been vaccinated. Some TTS cases have been reported in men and further analysis is required to determine any sex-related risk,” states NIAC advice.
The latest safety notice from AstraZeneca notes that a combination of thrombosis and thrombocytopenia, in some cases accompanied by bleeding, has been very rarely observed following vaccination with Vaxzevria.
“This includes severe cases presenting as venous thrombosis, including in unusual sites, such as cerebral venous sinus thrombosis and splanchnic vein thrombosis, as well as arterial thrombosis, concomitant with thrombocytopenia. Some cases had a fatal outcome. The majority of these cases occurred in the first three weeks following vaccination and occurred mostly in women under 60 years of age.”