[watwut]

Change in behavior can change basic reproduction number. That is what happened with SARS. Making basic reproduction number smaller is whole point of those curfew laws and of closing shops we now have. It is also the point of washing hands often and keeping distance.

It is defined as "expected number of cases directly generated by one case in a population where all individuals are susceptible to infection". And that is possible to influence by behavior. If no one even meets anybody, no sick person can generate next case. If people live in over-crowded houses, one person will infect many more.