In a statement late this afternoon the National Advisory Committee on Immunization recommended that AstraZeneca COVID-19 vaccine should not be used in adults under 55 years of age at this time while the indigence of blood clots reported in Europe is investigated further.
Summary of rationale
In a release NACI noted: “Rare cases of serious blood clots, have been recently reported in Europe following use of AstraZeneca COVID-19 vaccine. Cases identified so far have been primarily in women under the age of 55 years; although cases in men have also been reported and have mostly occurred between 4 and 16 days after receipt of vaccine. This adverse event is being referred to as Vaccine-Induced Prothrombotic Immune Thrombocytopenia (VIPIT)Footnote. This condition is associated with the development of antibodies that “activate” platelets, which stimulate the formation of clots and result in thrombocytopenia. The mechanism of action is similar to heparin-induced thrombocytopenia (HIT). The exact mechanism by which the AstraZeneca vaccine triggers VIPIT is still under investigation. At this time, no other risk factors have consistently been identified in patients who develop VIPIT. This adverse event has not been identified following receipt of mRNA COVID-19 vaccines to date.”
“The rate of this adverse event is still to be confirmed. Based on information from the European Medicines Agency on March 18, 2021 it was originally estimated at approximately 1 per 1,000,000 people vaccinated with the AstraZeneca vaccine, however a higher rate of 1 per 100,000 was reported by the Paul-Ehrlich Institut in Germany. Additional information is currently being gathered to characterize more accurately the rate of VIPIT. Based on available information, the case fatality of VIPIT is approximately 40%, however, the case fatality may decrease with increased awareness of the adverse event and appropriate early treatment.
The decision could have an effect on immunizations in Ontario, although no one under 55, with a few exceptions, is being vaccinated now. Ontario is set to receive 500,000 doses of the AstraZeneca vaccine during the month of April.