Best covid 19 vaccine - Get the facts about COVID

Possible severe symptoms include shortness of breath, persistent stomach pain, severe or persistent headache, blurred vision, chest pain, leg swelling, easy bruising, and tiny red spots on the skin.

They do not work as well in test tube studies, but scientists are not sure whether that translates into lower protection for people.

Any object with that particular shape is identified, attacked, and neutralized.

The benefits of a second booster for younger, healthier populations are less certain.