The choice we face is stark. One option is to maintain a general lockdown for an unknown amount of time until herd immunity is reached through a future vaccine or until there is a safe and effective treatment. This must be weighed against the detrimental effects that lockdowns have on other health outcomes. The second option is to minimise the number of deaths until herd immunity is achieved through natural infection. Most places are neither preparing for the former nor considering the latter.
The question is not whether to aim for herd immunity as a strategy, because we will all eventually get there. The question is how to minimise casualties until we get there. Since Covid-19 mortality varies greatly by age, this can only be accomplished through age-specific countermeasures. We need to shield older people and other high-risk groups until they are protected by herd immunity.
Among the individuals exposed to Covid-19, people aged in their 70s have roughly twice the mortality of those in their 60s, 10 times the mortality of those in their 50s, 40 times that of those in their 40s, 100 times that of those in their 30s, and 300 times that of those in their 20s. The over-70s have a mortality that is more than 3,000 times higher than children have. For young people, the risk of death is so low that any reduced levels of mortality during the lockdown might not be due to fewer Covid-19 deaths, but due to fewer traffic accidents.