The immune system keeps a record of every germ it has ever fought off, in types of white blood cells (B and T lymphocytes) called memory cells. This means it can recognise and destroy the germ quickly if it enters the body again, before it can multiply and make you feel sick.

The EBOLA virus has been a threat to humanity. When the Ebola epidemic appeared, people around the world faced historic risks. However, each type of virus has different characteristics and ways to prevent it to limit risks to humans.

People with cancer often have severely weakened immune systems, so the risk of infection is very high. Therefore, vaccination against certain strains of viruses is extremely important for cancer patients. However, which vaccines are appropriate and safe for them?