Blood clots are an extremely rare but serious side effect of AstraZeneca's COVID-19 vaccine, regulators announced on Wednesday.

The benefits of AstraZeneca's vaccine still outweigh the risks, the European Medicines Agency (EMA) said in a press release. Still, the agency's safety committee said it's important to know the signs of a possible clot.

A blood clot occurs when the blood thickens and forms a semi-solid mass. It can be a helpful response to stop bleeding in the case of injury, but these blockages can cause problems if they cut off blood flow to a vital area.

Blood clots can cause blockages in the legs, abdomen, and lungs. Most of the blood clots associated with the AstraZeneca vaccine have occurred in veins in people's brains.

These clots, known as cerebral venous sinus thrombosis (CVST), can lead to stroke, seizures, and death.

So far, most of the clots reported have occurred in women under 60 years of age within two weeks of vaccination.

Since young people are more likely to experience this side effect, UK vaccine regulators recommend that people under 30 do not get the AstraZeneca shot unless they've already received their first dose.

Blood clot symptoms include shortness of breath and headaches
The EMA said patients who got the AstraZeneca vaccine should seek medical assistance immediately if they have the following symptoms:

- shortness of breath
- chest pain
- swelling in your leg
- persistent abdominal (belly) pain
- neurological symptoms, including severe and persistent headaches or blurred vision

Some mild side effects, like pain at the injection site or other body aches, are common in the days post-vaccine.

But if you experience severe or persistent symptoms around four to 20 days after vaccination, you should seek medical attention, according to the World Health Organization.

Blood clots are typically treated with anti-clotting medication. Complications can be avoided if the clot is caught early.

This article was originally published by Business Insider.

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