The first dose of AstraZeneca’s COVID-19 vaccine was associated with a “very small” increased risk of bleeding and other rare blood disorders, the researchers said.
The findings, published in Nature Medicine on Wednesday, stem from a study in Scotland involving 2.53 million people who received the first doses of COVID-19 between December 8 and April 14, representing 57.5% of the country’s adult population. A total of about 1.7 million people received the AstraZeneca vaccine, and about 820,000 people received the Pfizer vaccine.
While the AstraZeneca COVID-19 vaccine is not yet approved for use in the United States, an independent committee advising vaccination in the United Kingdom has previously recommended that those aged 1
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The researchers reported an increased risk of abnormally low platelet counts within six days of vaccination with the AstraZeneca product. There were 1.33 more events of thrombocytopenia per 100,000 than expected. The researchers also found a frequency of 1.13 cases per 100,000 of so-called idiopathic thrombocytopenic purpura (ITP) or a blood disorder involving an unusual drop in platelet count, according to Hopkins Medicine. ITP is “most pronounced” about 21 to 27 days after vaccination, but was observed seven days after vaccination.
“This very small risk is important, but should be seen in the context of the very clear benefits of the ChAdOx1 vaccine,” the study authors wrote.
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The problem is more common in older adults; The researchers noted ITP during the AstraZeneca vaccination period for 40-49 year olds with 0.62 more events than expected per 100,000 doses, and there were 0.46 more events than expected per 100,000 doses in the adults studied.
The study authors reported 22 patients with an unusual drop in platelet count, although almost half had previous prescriptions that could lead to the problem. The study suggested that very few patients with ITP were prescribed ITP therapies after receiving the AstraZeneca vaccine.
The researchers noted three deaths after ITP, although not due to ITP, and deaths occurred in both vaccinated and unvaccinated people over the age of 70.
“The first dose of ChAdOx1 was found to be associated with small increased risks of ITP, with presumed evidence of an increased risk of arterial thromboembolic and haemorrhagic events. Given these small increased risks for ChAdOx1, alternative vaccines for individuals at low risk of COVID-19 to be justified when supply allows “, write the authors of the study.
The increased risk of the so-called. Arterial thromboembolic events occurred within 27 days of receiving the AstraZeneca vaccine, although fewer cases occurred than expected (3288 vs. 3328), and haemorrhagic or bleeding events occurred within 27 days after vaccination, although fewer cases were observed as expected (301 vs. 349).
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No such problems have been found with the Pfizer vaccine.
The researchers were unable to draw definitive conclusions about a clotting problem, including the rare but deadly cerebral venous sinus thrombosis, CVST. Six cases of CVST have occurred in people vaccinated with the AstraZeneca product, and researchers suspect that the result is likely to be ‘extremely rare’.
The study authors suggest that public health officials inform people about the “relatively small increased risks associated with the AstraZeneca vaccine.