What these people are urging is that the Covid19 virus be allowed to spread freely among those who are least are risk of serious illness or death, thereby achieving herd immunity.
Herd immunity acquired naturally through the spread of a novel infectious agent depends on the acqusition of immunity by survivors of the infection, which thus limits viral spread, since the proportion of the population to which the virus can be spread is reduced. This effect is measured by changes in the so-called Reproduction number or R0, which is the number of persons to whom each infected person passes the virus. As the virus spreads and the proportion of the population with immunity rises, R0 falls and, with it, the number of new infections. Ultimately, R0 reachs a value of one at which point the number of new infections stabilizes at a low level relative to the number at the height of the epidemic. At this stage the virus is said to be in a state of endemic equilibrium, meaning it won't go away but the number of new infections will not flare up as during the epidemic, but remain at a more or less constant low level. In due course, it is hoped that an effective anti-Covid19 vaccine will be available. Then R0 can be driven well below 1.0 and the disease will become quite rare.
One question this strategy raises is how close is the world or any particular country to achieving herd immunity. According to the Johns Hopkins University Corona Virus Resource Center, the total number of Covid19 cases worldwide is 35 million. or about zero point four percent of the world's population. That implies we are very far from worldwide herd immunity, which would require perhaps four and a half billion infections, or 60% of the world's population. Or so it is believed. However, some research suggests that due to differences among individuals and groups in their social interactions, herd immunity requires infection of only about 40% of the population of concern, or three billion infections worldwide, but that is still vastly greater than the number of infections reported by the Johns Hopkins University Corona Virus Resource Center.
But the number of infections worldwide may be much greater than the data from Johns Hopkins suggest. According to an announcement today from the World Health Organization, global infections now total 750 million, or more than 20 times the Johns Hopkins University estimate. That number, combined with the lower estimate of the numbers for herd immunity, implies that worldwide, the population could already be one quarter of the way to herd immunity. If that is correct, and if as proposed by the scientists calling for an end to lockdowns we protect the vulnerable part of the population, which is to say those over 60 years of age, then we could be shot of Covid19 as a major problem quite soon.
Related:
The Great Barrington Declaration
As infectious disease epidemiologists and public health scientists we have grave concerns about the damaging physical and mental health impacts of the prevailing COVID-19 policies, and recommend an approach we call Focused Protection.
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