Lack of Herd Immunity to COVID-19



Deepak Bhatt, MD, MPH: You made a lot of key points. First of all, new knowledge is being accrued every day. Some of what you cited are data just from today, or this week, or this month. The rate of new knowledge is incredible. Sometimes the knowledge is a bit contradictory, but that's not surprising. That's often the case when new diseases are described, or even when old diseases are being researched if new information comes and sometimes supplants or complements old information or research. You laid out the risk factors nicely. Some people throw obesity in there as a risk factor too, particularly the extremes of obesity. Obviously, there's some overlap with diabetes and high blood pressure as well in that respect.

You’re quite right: nursing homes, in some cases, have been decimated. That's been the source of many different outbreaks, so we have to be careful for people who are living in nursing homes where, if COVID-19 [coronavirus disease 2019] is in the community and is introduced into a nursing home, that can be a real death knell.

For the age part, that message has gotten out there, but it is perhaps to a point where young people think they are immune to the complications of COVID-19, which certainly isn't the case. People who are younger can certainly be hospitalized and develop complications. It's true: the mortality rate is much lower than people, say, in the nursing home age range, but still, if enough people at a young age are getting infected, we will hear more and more stories of deaths.

C. Michael Gibson, MS, MD: Deepak, there is important news today talking about young people and getting infected. Some people have said, “You know what? Let the young people go back to college. Let them get infected. We'll develop herd immunity.” Obviously, this was something that was tried in Sweden, but to keep us up to date, just within the past few hours, in the biggest study ever out of Europe with 61,000 people chosen at random from all over Spain, there was a 5% prevalence of the disease. Here's the deal: Spain was hit hard, and they had a lot of people die. People would think, “My God. With that kind of devastation, wouldn't more people have antibodies?” The answer is no.

The concern, and what the editorial wrote and what the authors concluded, is that we aren't anywhere near herd immunity of 50% to 70%. In the words of the reviewers and editorialists, any attempt to create herd immunity does not seem to be well-founded. They were strong in their wording. They said it would be unethical. I was stunned. I would have thought a place like Spain would be much further along.

To be fair, in some of the populous areas, the rate of antibody positivity was 15%. In those high-risk communities, it was higher, but it is nowhere near the 50% to 70% we would need, outside of a vaccine, to have herd immunity.

Deepak Bhatt, MD, MPH: That’s a great point. There were some people hoping that herd immunity would save us, but in fact, the numbers you cited essentially promise and assure us that there would be a second wave and maybe a third or fourth wave. People sometimes forget about the 1918 flu pandemic for which the first wave was kind of bad, but it was the second wave that did it, especially in places like Philadelphia, where they had a parade celebrating surviving phase 1, in part. That parade seemed to incite a large number of deaths in that second wave. There is a lot we can learn from history. Obviously, coronavirus isn't influenza per se, but some of the public health lessons that people who were alive learned have, to some extent, been forgotten.

C. Michael Gibson, MS, MD: I'll add one other fascinating recent tidbit from this weekend. In terms of severity of disease, the genetics have pointed to an ABO blood group association. That's now being challenged a bit, but there was fascinating work this week showing homology with, get this, Neanderthal DNA.

Deepak Bhatt, MD, MPH: Really?

C. Michael Gibson, MS, MD: There's a certain 60-fragment DNA section, and if you have homology with that from some of our ancestors, Neanderthals, you had a 2 or 3 times higher risk of severe disease, particularly if you had 2 alleles. Those of us somehow from the northern environs where you had more Neanderthal penetration, and even southern parts of some of Asia, had a higher risk of developing severe complications. This is not something I was expecting, but those are the 2 genetic risks so far that have been identified.

Deepak Bhatt, MD, MPH: Does that tell us anything deeper? Is there something perhaps older going on here?

C. Michael Gibson, MS, MD: That's a part of the world, particularly in Asia, where you have a lot of these bat reservoirs of coronavirus. You can imagine that, for millennia, areas like that have been doing battle with new variants of coronavirus. A lot of our common colds, 20% of them, are coronaviruses. You have to wonder, the first time we had that coronavirus variant, it may have been like this coronavirus. They may have been very bad common colds.

There are also some data that suggested from the research that these genetic variants confer a survival advantage for some other viral infections. What allows you to survive some other viral infection may put you at risk for having too much of an immune response to the COVID-19 infection. Obviously, there are societal influences, but let's not discount the genetic influences.

Transcript Edited for Clarity

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