A Note On Herd Immunity

Environmental & Science Education, STEM, Medicine, Health. Society

Ed Hessler

In a recent opinion essay in the Washington Post's coronavirus series, Abraar Karan (Brigham and Women's Hospital and Harvard Medical School) and Julie Parsonnet (Stanford Health Care) begin with an attention-grabbing assertion; "it's long past time that we do away with the concept (of herd immunity) as a goal for the pandemic." 

The concept of herd immunity, they write "is primarily used in infectious-disease modeling, and it refers to the point at which enough people have immunity such that disease transmission can't be sustained." They argue that the use of the concept "is most useful in closed populations (nursing homes, herds of animals for example)." It has become," in their words "an outsize talking point."

So where should attention be directed? "Rather than herd immunity....efforts on building community protections through vaccinations and public health interventions to help stamp out transmission chains and prevent ongoing infections." To live in societies which are "no longer dominated by the virus" it is most important that we understand virus transmission "and address this in locally led public health efforts." Our effort should be on vaccinating "as much of the world as possible as quickly as possible," transfer appropriate technologies, provide supplies, and scale up vaccine accessibility in nations which have not had necessary access.

The authors close by noting that "Among the many important lessons that covid-19 has taught us is that we are intimately connected with those across seas and borders. This is sometimes easy to forget in the United States, where there have been far fewer serious infectious-disease outbreaks than in many other parts of the globe. This virus has humbled us, and we must continue to respect it even while we commit our best efforts to control it. But we don’t need to pray to the false god of herd immunity to do so."

The essay is reasonably short and includes some important discussion on variables influencing herd immunity, the slipperiness of herd immunity (variants change the game), viral resurgence, the limited time-frame of herd immunity (single vaccinations do not work forever), and recurrent epidemics. 

The messages is standard: get vaccinated and practice pubic health interventions when warranted. 

Addition. On May 18, 2021 Geoff Brumfiel for NPR also ran an essay that scientists say "fixation" on herd immunity to end. We have boiled down the end of the pandemicto  those two words. By the way the idea did began "with cows, not people. In 1916, veterinarian Adolph Eichhorn and colleagues noticed that a herd of cattle could become collectively immune to a disease if enough animals survived the initial infection." I hadn't realized or forgotten that the threshold for herd immunity during the pandemic has "fluctuated from as low as 20% to as high as 90%." The term faded for a while but gained new life in the United States with the approval of vaccines. Anthony Fauci, for example, estimated that it would require vaccinations of 75% to 85% nationally."

Brumfiel provides a summary of the politics herd immunity has played in the pandemic. The idea, appealing to many politicians, was to simply let the coronavirus run unchecked until herd immunity was achieved both in Great Britain and the United States.

The report has a section on differences between computer models and real life. The reality is that we don't achieve such levels with the flu. The models serve as warning signals, signals for policy makers to not only note but respond appropriately.

An appeal of the idea "is clear," writes Brumfiel. "Achieving herd immunity sounds like a simple goal that spells the end of the coronavirus. It feels concrete — something to grab onto in a time filled with so much uncertainty, a finish line for which to strive."

What should we worry about and where should we place our efforts? Getting vaccines into people's arms and when necessary making use of the tried and tested preventatives. Masks, physical distancing, avoiding large crowds have one thing in common: lowering risk.