Herd immunity (a medical term) requires around 60% of the population be immune to a disease before it will not spread as a pandemic. Assuming covid 19 causes long term immunity, e.g., >2 years, then the worlds population will develop herd immunity after around 5.4 billion people have been infected. The number of deaths would be in the millions. If a viable vaccine is developed, herd immunity may be achieved with fewer deaths.

The covid 19 immunity period is currently unknown, it will take several years to learn (e.g., 2 or more).

Oxford University is starting trials of a possible vaccine. It will take time to know if it is effective and safe, especially since this round of trials is not being done on humans. In the mean time, wear a mask and practice social distancing.