A reproduction number of 1.21 means that a group of one hundred people who have corona among members infect an average of 121 others. They in turn infect 146 people, who then transmit the virus to about 177 people. With each step, the number of infected people increases, and with it the risk of infecting others. The further the number gets above 1, the faster the virus spreads. In July last year, during the ‘dancing with Janssen’ wave, the reproduction number reached a record high of 3.