Published: 27 April 2021

Safety Information

Monitoring Communication

COVID-19 vaccines and rare cases of blood clots with bleeding: no current risk with Comirnaty (Pfizer/ BioNTech) vaccine

27 April 2021

Medsafe has completed a review of the risk of rare cases of blood clots with bleeding
( Thrombosis with Thrombocytopenia Syndrome; TTS), reported internationally with some COVID-19 vaccines. At the current time, there is no evidence of a risk of TTS with the Comirnarty (Pfizer/ BioNTech) vaccine.

Additional information

Medsafe has finished an initial evaluation of international reports of a rare syndrome of blood clots (thrombosis) occurring with bleeding (due to thrombocytopenia) and platelet factor 4 antibodies. To date, all the cases that have been reported after vaccination are linked to the first dose of Vaxzevria (AstraZeneca) or the Janssen COVID-19 vaccines. These vaccines are not currently used in New Zealand.

There have been reports of blood clots internationally after vaccination with Comirnaty. Medsafe’s assessment is that there is no indication that these cases are in any way similar to the TTS cases reported with the other COVID-19 vaccines. This assessment was endorsed by New Zealand’s COVID-19 Vaccine Independent Safety Monitoring Board (CV-ISMB) on 22 April 2021.

Up to 22 April 2021, the Centre for Adverse Reaction Monitoring (CARM) has received three cases of thrombosis (one stroke, one deep vein thrombosis and one cerebral venous sinus thrombosis). There was no evidence of bleeding in any of these cases. Following review by CARM and the CV-ISMB, none of these cases was considered to be related to vaccination. The number of cases of thrombosis reported following vaccination is lower than the expected number occurring without vaccination. There are over 3,000 cases of thromboembolism and more than 10,000 cases of stroke requiring hospital treatment per year in New Zealand.

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Regulator actions

Medsafe continues to monitor this safety signal and remains in contact with international regulators.


Consumers and healthcare professionals are encouraged to report suspected adverse events following immunisation to the Centre for Adverse Reactions Monitoring (CARM).

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