Whether or not a person is affected by germs depends on several factors:
How many germs they are exposed to and how powerful (virulent) the germs are.
If a person is exposed to many powerful germs, they are more likely to get sick.
Their general health.
If someone is generally healthy and eating and sleeping well, their immune system will function better than the immune system of someone who has other health problems, eats poorly, and doesn’t get enough sleep.
Whether they are immune to the germ
If someone has an illness, they develop antibodies to it. When they are exposed to the germ again, their body’s antibodies recognize the microbe and destroy it and they do not get sick. This is how vaccines work, too. Vaccines give your body a small dose of a germ so you can develop antibodies.
Schools and child care centres have been found to be one of the main causes of the spread of diseases like the flu to the rest of the community.