The AstraZeneca coronavirus vaccine may lead to an increased risk of developing the serious neurological condition Guillain-Barré Syndrome (GBS).
Scientists believe the jab's Trojan horse delivery system could be to blame and that the discovery may apply to similar vaccines.
GBS is an ultra-rare condition where the body's immune system attacks the nerves, leading to muscle numbness and pain. Its rapid onset can quickly paralyse muscles and hinder the ability to swallow and breathe.
