[Ernesto]

If mask very effective how the hell 900 people get infected by Jurong Port?

You put on condom you can prevent pregnancy but no 100% your partner wont get pregnant if one not careful. Putting mask is the principal. If one dun put it on when necessary according to the basic rule ,it will cost yourself "pregnant" with virus . Adding to that it spreads ....,..
So lets not be stiff necked if not we will be living in a more chaotic environment.