There are 200 Viruses, vaccines only exist for 20 or so. For some you can hardly build immunity (e.g. Dengue fever). "Sure, those who survived the disease will

There are 200 Viruses, vaccines only exist for 20 or so. For some you can hardly build immunity (e.g. Dengue fever). "Sure, those who survived the disease will be immune afterwards." There have been reports of re-infections in China and Japan. This may be mistakes - the never were cured - but this could also point to something more severe. Proceed with caution.