To be or not to be exposed to viruses?

Well, as you were saying in your first paragraph, many viruses have less virulent strains that if you catch it once, you wont get sick from a virus similar to it. When you catch a disease, your immune system produces antibodies, which are white blood cells that remember the disease and won't let you get sick from the same thing again. However, if you are not exposed to the same virus within 5 years, those antibodies die and you lose protection, so you can never have a "fully equipped defense mechanism", but then again it is also impossible to live somewhere that is "completely germ free", unless you live in a hospital your who life. I say it is better to be exposed to more viruses therefore you have more protection.