Joel A. Bryan, Using Radioactive Decay to Investigate Exponential Functions, The Mathematics Teacher, Vol. 106, No. 1 (August 2012), pp. 52-58 ...

The question of when the dissipation is effective enough to cause uniform exponential decay of energy is examined. Because of the locally distributed nature of energy dissipation, the problem lacks ...

We just need to keep transmission rates below the tipping point between exponential growth and exponential decay: where every person with Covid-19 infects fewer than one other person, on average.