There is currently a worldwide pandemic, which started at the beginning of 2020, caused by a corona virus called Covid-19 (hereafter covid). This virus is highly transmissible (and becoming more so) and the disease can be serious, causing hospitalization and sometimes death. There are two ways in which to combat a pandemic. The first is to quarantine those who are infected, to isolate victims from the rest of the population so that they cannot pass on the disease. This measure was first introduced in the fourteenth century when the plague reached Europe, and it did not work. In the twenty first century, variations on this theme have been tried, but the pandemic is so widespread that quarantining cannot be completely effective. Lockdowns and contact tracing, in which the range of activities that citizens normally engage in are curtailed (more or less severely), and border closures are two main tactics that countries have tried as partial quarantines. These are effective in slowing the progress of the disease and in some instances have suppressed outbreaks altogether, but they are hard to tolerate. Border closures in particular can separate families for long periods, and extended lockdowns have negative economic and social consequences. If it were not for historic low interest rates, modern economies would not be able to endure lockdowns for very long, and as it is, there are limits to how much activity can be curtailed before economic collapse.
If the disease were allowed to free rein, then eventually herd immunity would be reached, or at least it is assumed that eventually herd immunity would be reached. Herd immunity is a condition in which a high enough percentage of a population is immune from the disease for it to be the case that it cannot cause an epidemic (epidemics affect particular populations, while pandemics reach across many populations). An epidemic can only happen if each person who has the disease in question infects more than one other person. If at most one other person is infected, the disease will reach a steady state, or decline. The threshold for herd immunity, the percentage of the population that must be immune before the herd as a whole is immune, depends on the infectiousness of the disease. This is measured by R, the number of people that, on average, an infectious person transmits the disease to: the greater the value of R, the more rapidly the epidemic spreads. An individual who gets the disease (caused by a virus) and recovers will have a degree of natural immunity: her immune system will ‘recognise’ the virus next time she encounters it and mobilise to fight it. In this way people will not become (so) ill and hence not pass on the disease, and eventually the herd immunity threshold will be reached. Countries that did not take covid seriously in the early days, like the US and Brazil, adopted by default the policy of dealing with the disease by giving it free rein.
There are two problems with allowing covid to spread through the population to achieve herd immunity as an overall strategy for dealing with the pandemic. First of all, as I have mentioned, the disease can be serious: the mortality rates range from 1-10%. The lower end of scale reflects the situation in countries with the best health care, and these numbers are coming down owing to new ways to treat the disease. However, when there are millions of people are infected, even in countries with the very best health care, there are many thousands of deaths. In the US, for example, over 600,000 people have died. In addition one needs to take account of the number of people who become seriously ill, and require medical treatment. As the number of infections increase, health care systems become overwhelmed and victims will remain untreated, as is attested by harrowing scenes broadcast in the media. It is clear that no country can simply let the disease have its way and preserve a stable social and political structure: the disruption and chaos would be worse than that caused by the Spanish Flu and perhaps comparable to the bubonic plague of fourteenth century. There is yet another reason why this strategy will not work. Viruses mutate. Given the very high incidence of covid, the ‘opportunities’ for mutation are correspondingly great. We have already witnessed more infectious variants of the disease. This is the way selection works: more infectious variants will naturally become the dominant strain. Allowing the disease to have free rein therefore allows more opportunities for mutation and more infections, in a disastrous synergy. Furthermore, the immunity conveyed by infections by earlier stains may not be sufficient to fight the newer variants. The only effective weapon against covid is vaccination.