Researchers say the first dose of AstraZeneca’s COVID-19 vaccine was associated with a “very small” increased risk of bleeding and other rare blood disorders.

test result published Wednesday in Nature Medicine stems from a study in Scotland involving 2.53 million people who received their first doses of COVID-19 vaccines between December 8 and April 14, comprising 57.5% of the country’s adult population. In total, about 1.7 million people received the AstraZeneca vaccine, and about 820,000 were given the Pfizer vaccine.

While the AstraZeneca COVID-19 vaccine is not yet authorized for use in the US, an independent committee on vaccination advice in the UK previously recommended that people aged 18-39 with no underlying health problems should be given the vaccine. An alternative should be provided for patients with rare cases associated with clotting and a low platelet count. According to the study, as of April 21, the UK regulatory body (MHRA) had received 209 reports of clots and low platelet levels against the background of 22 million first doses and about 7 million second doses of the AstraZeneca vaccine.

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Researchers reported an increased risk of abnormally low platelet counts within six days of vaccination with AstraZeneca’s product. There was a 1.33 higher-than-expected incidence of thrombocytopenia per 100,000. Researchers found 1.13 cases per 100,000 of so-called idiopathic thrombocytopenic purpura (ITP), or a blood disorder that involves an abnormal drop in the number of platelets, per Hopkins Medicine. ITP was “most evident” at 21 to 27 days after vaccination, but was observed seven days after vaccination.

“This very small risk is significant but should be viewed in the context of the very clear benefits of the ChAdOx1 vaccine,” the study authors wrote.

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This problem was more common in older adults; The researchers noted ITP during the vaccination period of AstraZeneca for children 40-49 years old was 0.62 more events expected per 100,000 doses, and in the adults under study, there were 0.46 higher events expected per 100,000 doses.

The study authors reported an abnormal drop in platelet count in 22 patients, although about half had prior prescriptions that could have brought on the issue. The study shows that very few ITP patients were prescribed ITP treatment after receiving the AstraZeneca vaccine.

The researchers noted three deaths after ITP, although not due to ITP, and deaths in both vaccinated and non-vaccinated people over the age of 70.

“The first dose of ChAdOx1 was associated with small increased risks of ITP, with suggestive evidence of an increased risk of arterial thromboembolic and hemorrhagic events. Given these small increased risks for ChAdOx1, individuals at low COVID-19 risk were There may be alternative vaccines for cancer. When supply is permitted, warranted,” the study authors wrote.

The increased risk for so-called arterial thromboembolic events occurred within 27 days of receiving AstraZeneca vaccine, although fewer cases than expected (3,288 versus 3,328), and hemorrhagic, or bleeding, events occurred within 27 days of vaccination, although fewer cases than expected. More views (301 vs 349).

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No such problems were found with Pfizer’s vaccine.

Researchers could not draw firm conclusions about the relationship of clotting issues, including the rare but fatal cerebral venous sinus thrombosis, CVST. Six cases of CVST occurred in individuals vaccinated with AstraZeneca’s product, and researchers suspected the result was “extremely rare.”

The study authors suggested that public health officials notify people with the AstraZeneca vaccine “associated with a relatively small increased risk.”