Would 'herd immunity' work, and at what cost?

As some political candidates and other public figures push for letting the COVID-19 pandemic run its course - with the aim of trying to get daily life back to normal as soon as possible, without public health restrictions - public health experts are wary of such plans.

Herd immunity against COVID-19 will be achieved when either through use of a vaccine, widespread infection or a combination of both enough people will have been exposed to the novel coronavirus that causes the disease and become immune to it so that sustained transmission through the population will no longer be possible.

The first major hurdle in getting to that status is the number of people that would have to have developed immunity.

Estimates for what percentage of the population would need to be immune for transmission to no longer be viable have ranged from approximately 70-90 percent, according to sources including Mayo Clinic; a National Institutes of Health-published study by University of Chicago researchers Haley Randolph and Luis Barreiro; and Johns Hopkins Bloomberg School of Public Health professors Gypsyamber D'Souza and David Dowdy.

Even after hundreds of thousands of deaths and millions of infections in the U.S. and around the world so far this year, a Spanish study published this month in The Lancet medical journal found only about 5 percent of people in that country have antibodies against COVID-19.

That lines up with what Missouri Department of Health and Senior Services Director Dr. Randall Williams said last month when he said herd immunity would be achieved when 60 percent of the population will have been exposed to the disease, but less than 5 percent of all people have been - and the percentage won't be anywhere close to 60 percent in the fall or winter.

The authors of the Spanish study in The Lancet wrote the low prevalence of COVID-19 "in the context of an intense epidemic in Spain might serve as a reference to other countries. At present, herd immunity is difficult to achieve without accepting the collateral damage of many deaths in the susceptible population and overburdening of health systems."

Sweden is an example of one country that has tried achieving herd immunity through infection, rather than waiting to try through a vaccine.

An analysis published this month in the Clinical Infectious Diseases medical journal by University of Virginia School of Medicine professor Peter Kasson and Shina Kamerlin, of Sweden's Uppsala University, looked at how Sweden's approach affected deaths and hospital demand there.

The Swedish government only closed high schools and universities and advised people with symptoms and individuals over the age of 70 to isolate themselves, according to the study.

"Benefits of the individual-response approach include increased flexibility; drawbacks include decreased coordination in the maintenance and strategic relaxation of controls. Predicted deaths and ICU demand are also greater with voluntary adherence than with stringent mandates until adherence rates exceed 75 percent," according to the study's authors.

Sweden's hospitals were not overwhelmed, but that's because of individuals' adherence to isolation at home, Kasson said in an interview with the University of Virginia Health System.

"Whether mandated or voluntary, self-isolation of a substantial fraction of the population profoundly reduces ICU need and mortality if applied early and with substantial adherence rates. It therefore also follows that greater self-isolation in Sweden would have commensurately reduced deaths," Kasson and Kamerlin added.

The University of Chicago professors noted when it comes to attaining herd immunity from COVID-19, "a regard for finite healthcare resources cannot be overstated, as this policy inherently relies on allowing a large fraction of the population to become infected. Unchecked, the spread of SARS-CoV-2 will rapidly overwhelm healthcare systems. A depletion in healthcare resources will lead not only to elevated COVID-19 mortality but also to increased all-cause mortality."

Another complication is that the people most at-risk from COVID-19 are not all relatively isolated at home or congregated in places such as nursing homes, and they're not all of a certain age group.

A study published last month by the Kaiser Family Foundation found of 37.7 million U.S. adult workers especially at risk from COVID-19 - because of having conditions such as diabetes, chronic lung or heart disease, obesity, asthma or cancer - 27.7 million were between the ages of 18-64.

The study considered all workers 65 and older as also being at higher risk - which added up to the remaining 10 million people.

"In addition to at-risk people who are workers themselves, there are millions more at-risk adults who themselves are not workers but who live with workers. This indirect exposure could be just as serious of a risk as going to work themselves," the Kaiser Family Foundation study added - with an estimate of there being 12 million more at-risk adults who are not workers but live with at least one full-time worker, with 6.5 million of those people being older than 65, and the other 5.5 million being at-risk non-elderly adults.