There seems to be a simple—as in elegant—way of getting some perspective on COVID-19 and herd immunity, which is defined as,
A situation in which a sufficient proportion of a population is immune to an infectious disease (through vaccination and/or prior illness) to make its spread from person to person unlikely. Even individuals not vaccinated (such as newborns and those with chronic illnesses) are offered some protection because the disease has little opportunity to spread within the community. Also known as herd immunity.
According to WorldOMeter, the United States has 1,546,420 Coronavirus Cases.
Throughout April the number of daily tests has averaged around 150,000, with the share of positive tests staying around 20%. That suggests America is testing only people who are probably infected (in Taiwan, for instance, one in every 132 tests is positive), which in turn suggests that many mild or asymptomatic cases are going undetected. America may have 15 to 20 times more actual infected people than confirmed cases.
1.5 million times 20 makes 30 million infected.
At best, approximately 30 million individuals in the US have some immunity to COVID-19.
The 30 million number is predicated on these two assumptions:
1. That the infected number includes the dead and the recovered. This seems reasonable.
2. That the Economist’s multiplier above is correct. That likelihood is good, too.
Thirty million people with immunity is less than 10 percent of the U.S. population. For there to be population-level immunity to COVID, “at least 70 percent of the population needs to be immune.”
We are still very far from achieving herd immunity.