Herd immunity in this case is a fruitless idea without a vaccine. Vaccines are, as you might know, an infusion of the very disease in question. Since there is no vaccine for CoV-2, the only way to achieve herd immunity is for the vast majority to become infected with it, which is a horrendous idea, as it has a high fatality rate. Without a vaccine, the only way forward is to stamp out the contagion through isolating ourselves from it, so that it dies out for lack of hosts.