Misplaced Hopes for COVID Herd Immunity; Napkin Calculation

Herd immunity is all the rage. (NYT) When Could the United States Reach Herd Immunity? It’s Complicated. According to charts like these, the future is predictably bright. Not so fast.

When I saw the Penn and Teller  magician duo  show in Vegas, Penn began by insulting the audience (paraphrasing): “If you knew any math, you wouldn’t be in Vegas.” The audience laughed. Since you haven’t paid a hundred bucks to read this, and can X the tab any time you want, I’ll try to be more polite.

After all we’ve been through since Feb 2020, you really shouldn’t give the NY Times chart, or Alabama’s in-state projection, any credence. But, you argue, it is the product of experts? Epidemiologists are honorable scientists who are experts at many sub-specialties and technical tools of the science of epidemiology. One thing they are not experts at  is COVID prediction.

Expertise implies accuracy.  We have only trends, which like fads, continue for a while, ending unpredictably. Legend has J.P. Morgan on the stock market: “It will fluctuate.” Governor Cuomo already knows this. (CNN) Gupta: I’m stunned Gov. Cuomo said this about health experts; Sometimes You Just Have to Lie.

These reports directly challenge the NY Times chart:

So why is the NY Times chart so beguiling? Are we sucked in by an attractive graphic, even though it offers no accounting for mutant strains? Perhaps, like propaganda, it works in the absence of accessible alternative information.

The alternative will come in the form of a napkin calculation. The result will not be fact, but an alternative to the chart, which, in our ignorance, has equal weight. Refer to (Nature) Fast-spreading  COVID variant can elude immune responses. Quoting,

Pseudoviruses with the full package of 501Y.V2 mutations were fully resistant to convalescent serum from 21 out of 44 participants, and were partly resistant to the vast majority of people’s sera, Moore’s team found.

Quoting from (BioRxiv) SARS-CoV-2 501Y.V2 escapes neutralization by South African COVID-19 donor plasma,

SARS-CoV-2 501Y.V2, a novel lineage of the coronavirus causing COVID-19, contains multiple mutations within two immunodominant domains of the spike protein. Here we show that this lineage exhibits complete escape from three classes of therapeutically relevant monoclonal antibodies. Furthermore 501Y.V2 shows substantial or complete escape from neutralizing antibodies in COVID-19 convalescent plasma. These data highlight the prospect of reinfection with antigenically distinct variants and may foreshadow reduced efficacy of current spike-based vaccines.

Let’s get a number out of these citations. The number will be plausible, not factual. It will be on a collision course with the NY Times chart. The number is 1/2.  With respect to the entire population of the U.S., and the number of silent cases, administered vaccines, recovered-diagnosed: divide this sum, the NYT orange line, by half.

The NYT chart orange line of total immunity implies an increase of community immunity from a current 40% to 75% in six months.. This is an increase of  6% per month, which we use to correct the NYT graph. With anticipation of widespread SARS-CoV-2 501Y.V2 and other mutations, the factor of 1/2 could imply we are currently, not at 40%, but  20% immunity. To make up the difference of 20%, at 6% per month, we need 3+ more months.  The implies herd immunity in November/December, not August.

This is possible, not factual, if COVID doesn’t have more tricks up its sleeve. It takes influenza A about 25 years to cycle through its range of antigen permutations.

Even with the not-quite promise of herd immunity, COVID-19 is likely to remain a nasty, prevalent disease,  sparing only those with lucky genes,  and those who are exposed as children.

“There are lies, damned lies, and statistics.

Mark Twain et al.


Leave a Reply