Oxford-AstraZeneca and COVISHIELD COVID-19 vaccines to add capillary leak syndrome as a potential side-effect.The agency is also including a warning for patients with a history of the ailment to not get those vaccines.Capillary leak syndrome is a very rare, serious condition that causes fluid leakage from small blood vessels (capillaries), which can result in the swelling of the arms and legs, sudden weight gain, low blood pressure, thickening of the blood and low levels of the albumin blood protein.Health Canada and the Public Health Agency of Canada have been monitoring the condition since it was raised as a potential safety concern by the European Medicines Agency in April.