Phase 3: Profit !

To be or not to be ?

This is a very common topic for anyone who had study game theory, but anyway I’ll talk about it here.

The Critical mass
The Flu infection will spread explosively only if the number of people infected reach a critical mass, (The critical mass is different between virus since it depends on form of infection).

Say,
if it’s lower than the critical mass, the cure rate will be larger than the infection rate, the virus is in control. (Since the new number of people get infected each day is somehow proportional to people already got infected)
if it’s higher than the cure rate, the whole population will eventually infected.

There are couple of ways to reduce infection, aka the chance of get infected. e.g. Using Surgical mask, or taking vaccination (if one ever discovered). Taking such measure not only allows one to reduce the chance of get infected, but reduce the chance of the great spread explosion.

Isn’t that a win-win situation?

No. The measure-taker had to pay cost (e.g. price of the vaccination, buying the mask etc ).

But the free-rider/slacker, pay nothing and avoid the explosion if there are enough measure-taker exist in the society. It’s called [W:Volunteer's_dilemma] in game theory.

Side note, the value for getting infected in “Enough People” and “Not Enough People” is different, since the chance of getting infected is larger.

So, if the society got enough people already taken vaccination(With people fully aware of the disease), the best move (cost-efficient) is not taking it.
While there are not enough people (e.g. under-development country), the best move is take it yourself.

In short,
if they take it, you don’t need to.
if they do not, you better do.

The best move probably is, “encourage” others to take the vaccine, while you don’t.

(in sense of cost-efficient but not ethical)