Question: What is the most contagious diease?

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  1. The most contagious micro-organism is probably something like the rhinovirus which causes colds or something harmless that we don’t even notice being passed around.
    The most contagious disease I would say is measles. Measles is passed between people through the air as people who are sick breathe. One way we measure how contagious something is is to calculate something called an R0. An R0 is the number of new cases of a disease generated from a single source during the infective life cycle, basically, if you get sick then how many people will you make sick? Measles has an R0 of 15ish so every time 1 person gets sick they will make 15 more people sick with measles.
    If you compare this to the worst flu that has ever hit the planet (Google 1918 Spanish flu) that had a R0 of only 3.
    The reason we don’t see lots of people with measles is because we have a very effective vaccine that protects us from infection.