In Maths, a vector is a direction towards something.
Similarly, in biology a vector is something that carries an entity from one place to the next. This can be from surface to surface, or between people.
There has been much public discussion about washing hands - and appropriately so.
But consider the example of the public lavatory. The contaminant is not COVID-19 in this common example, but the principle is the same.
THIS CONCEPT IS KNOWN AS THE CHAIN OF INFECTION.
A SIMILAR CHAIN OF INFECTION ARISES WITH RESPIRATORY VIRUSES.
It takes approximately two weeks for the infection to spread throughout Person A's lungs, before coughing and other symptoms present.
Needless to say, one infected person’s sneezes or coughs can affect many people - especially if they are grouped together in a closed space. From one person to many, an exponential chain of infection occurs - which can then become an epidemic and a pandemic.
Responsible people, those who understand the Chain of Infection, can use touch resonance to avoid further contamination. Touch resonance on contaminated fingers avoids further vectorisation by ensuring people do not touch any surfaces until the hands are washed and disinfected.
However we cannot assume that every person that uses the public lavatory is so hygienic. To protect ourselves, we should assume, each time we use a public loo, that others will have contaminated the shared surfaces: the flush button, cubicle latch, taps, towels and door handles.