Professor Philip Nolan:

The strategy is to keep the reproduction number as low as possible, so that is number one. Second, when case numbers are very low, it is very hard to estimate what the reproduction number is. As soon as it is above 1, we are encountering difficulty and the further it is above 1, the bigger the problem. I am not stretching out the time here. What really matters is the product of the number of cases and the reproduction number.