The first dose of AstraZeneca’s COVID-19 vaccine was associated with a "very small" increased risk of bleeding and other rare blood disorders, researchers say.

While the AstraZeneca COVID-19 vaccine is not yet authorized for use in the U.S., an independent committee advising vaccinations in the U.K.

regulatory body (MHRA) received 209 reports of clotting and low platelet levels against a backdrop of 22 million first doses and nearly 7 million second doses of the AstraZeneca vaccine, per the study.

"This very small risk is important but needs to be seen within the context of the very clear benefits of the ChAdOx1 vaccine," study authors wrote.

"First dose of ChAdOx1 was found to be 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, alternative vaccines for individuals at low COVID-19 risk might be warranted when supply allows," study authors wrote.

The heightened risk for so-called arterial thromboembolic events occurred within 27 days after receiving the AstraZeneca vaccine, though fewer cases cropped up than expected (3,288 versus 3,328), and hemorrhagic, or bleeding, events occurred within 27 days of vaccination, though fewer cases were observed than expected (301 vs 349).

Study authors suggested public health officials inform people of the "relatively small increased risks associated" with AstraZeneca’s vaccine