Giving CoViD vaccine to already recovered

Q1) Giving CoViD vaccine to already recovered pt is an example of primary or secondary prevention?

Q2) Since both Secondary attack rate and effective reproduction number are used to estimate infective potential of agent, why we have two different parameters?

  1. Primary to prevent reinfection

  2. Yes both convey same meaning just that:

Effective reproduction rate is an absolute number: 2 or 4 or 10 or whatever

SAR is a rate, secondary cases divided by susceptible population

Just like PPV and liklihood ratios… both convey similar meaning