The Alternative Pathway: Herd Immunity

Bradley Tanner, MD, ME, MBA
April 4, 2020

With such a highly transmissible virus and the need for health care intervention, we may have to accept the reality that the end of the epidemic will only come with herd immunity.

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The good news is we may already be on the way, and herd immunity may explain the evidence that the impact is slowing and will reverse its deadly rise soon. [Lourenco J, Paton R, Ghafari M, et al. Fundamental principles of epidemic spread highlight the immediate need for large-scale serological surveys to assess the stage of the SARS-CoV-2 epidemic. medRxiv. March 26, 2020:2020.03.24.20042291. doi:10.1101/2020.03.24.20042291.]

The virus is far too transmissible, and the solutions in terms of establishing immunity or preventing infection with antibodies, and treating the illness are far too far off to hope that we can somehow hide from this virus. In the time that it will take to develop and test a vaccine or drug solution, the virus will continue to spread, albeit slowly, and will eventually overcome any effort to stop it. The reality is that as long as we have some people who are not social distancing, it will continue to spread. And as I discussed, the vector for that spread is likely to be the treatment provided via the health care system and everyone involved [If you want to stop new cases, look at the health care system and anyone involved in testing, hospitals, clinics, or care of the dead].

I don't say that to blame folks who aren't complying with social distancing. I say that to recognize that some things have to stay open and, most importantly, we cannot isolate everyone from everyone actively involved in helping the sick - from the police to funeral directors. It would be cruel to isolate our responders, and honestly not possible.People have a right to go to the hospital and to request a test, even if that places the rest of us at risk. Rather than see this as blame, we must accept the reality that this virus is continuing to spread due to this activity.

So the first reality to accept is that no matter what we do in terms of social distancing, the healthcare system will continue to spread this virus far and wide. Similarly, we all need food, and we need food delivered to the stores, so anyone in that supply chain is also going to be participating in its ongoing spread. We have to accept that the ongoing spread is inevitable. I know I just said that, but it seems no one is willing to accept that reality no matter how obvious it is.

Once you accept that this is not a war where we can "defeat" the virus as if it were a country that we could overwhelm with missiles, you are left with hope in herd immunity. Here we are incredibly fortunate that the death rate is not enormously high. There is clearly a large portion of the population that is either already immune or asymptomatically clears the virus and achieves immunity. The benefit of a highly transmissible virus is it will rapidly achieve herd immunity.

We are indeed fortunate that the death rate is not 20% or 10% but far lower, more recently estimated at 0.66%. [Verity R, Okell LC, Dorigatti I, et al. Estimates of the severity of coronavirus disease 2019: a model-based analysis. The Lancet Infectious Diseases. March 30, 2020;0(0). doi:10.1016/S1473-3099(20)30243-7.] Yes, that means that some will inevitably die. We have to accept that reality versus the ongoing myth that somehow all this can be magically avoided through some kind of war or attack on the virus. We already accept deaths due to opioids, tobacco, automobiles, guns, and behaviors leading to diabetes, heart disease, and cancer.

We also have to repeat the reality a virus it's not a combatant. Instead, it is something that lives inside the lungs of people and is spread every time they cough. As folks get treated, they provide more and more of an opportunity to spread the virus to other people. War analogies are simply not helpful.

On the optimistic side, herd immunity is, in fact, achievable, and we probably have demonstrations of its success already. Although we've seen many deaths on cruise ships, we've seen that the numbers have been limited. Similarly, we've witnessed aircraft carriers can get infections, but we have not seen massive deaths. Given how transmissible this virus is in both cases, one must assume that pretty much everyone was infected. Similarly, given the viral load in hospitals, we have to assume that every healthcare worker has also been infected, and what we're seeing is that the majority come out just fine.

I don't mean to underplay the fear of healthcare workers. In fact, I understand the concern of healthcare workers. I was trained in the early days of HIV when it wasn't clear how the virus was transmitted, but it was clear how deadly it was to young men. But fear isn't rational. And we know that young people are at very low risk of dying from this virus. And healthcare workers are at risk for HIV, Hepatitis, Flu, and many other contagions. Personal risk and the emotional trauma of watching people suffer and sometimes die is an unavoidable part of health care delivery. But arguing that a virus that infected 100s who attended a convention isn't going to be spread to everyone in a hospital no matter how well they are protected is irrational. We cannot argue that we should social distance and avoid groups of more than 2 people, but ignore the health care environment. We simply cannot claim that a healthcare worker can be 100% protected against a patient on a ventilator that is spewing out untold millions of viruses. Just look at what kind of protection is offered to scientists who work with smallpox. We simply cannot provide that level of protection and actually run a hospital and treat people.

There have been many negative comments about Liberty University. In fact, they are doing a test of herd immunity by asking folks to come back. In the process, we will obtain some data about how much of the virus spread is causing illness, hospitalization, and death. Similarly, some churches in Florida will be seeing the impact of potential spread by opening their doors. What if people get infected and recover (the norm for younger people), and we learn something? Will we be willing to thank them and the people involved for taking a risk and telling us that actually herd immunity may be a means of protecting us, and we can go back to normal?

Alternatively, from the data, perhaps we can start to identify when areas have approached herd immunity. That will guide us in terms of releasing us from all of the social distancing. As an example, a place like New York seems scary; however, at this point for New Yorkers, it has most certainly spread to most of New York. That population is probably demonstrating some herd immunity. That would explain some of the drops in the death rate recently on several days.

Success in New York via herd immunity, strangely enough, does mean there is a risk - a risk from people who come back to New York from places that don't have herd immunity. They should be told to not come since New York resources are already stressed out. But in many parts of the US, we may be able to assume that the virus has been slowly spreading so that most people have some exposure, and many people have developed an asymptomatic or very mild case of the virus. The evidence to support that is that each new city has not seen the explosive growth that New York has seen in its early days. In fact, they all appear to be doing much better. We see the same thing worldwide. Slow, steady spread may be both achievable and optimal (as well as unavoidable)

The ongoing assumption is that success in other states and cities is due to social distancing since, in many (but certainly not all) distancing was in place early. This may indeed, have been helpful. But a more likely explanation is that the virus spread at a slower rate and enabled more people to develop immunity than in New York, which invariable had an enormous number of people coming into a city known for its congestion. The success that non-New York cities are seeing may be that herd immunity limited further spread.

With herd immunity, the risk remains for individuals with medical problems, especially the elderly. Isolation for them is still essential since we don't have early treatments or prevention efforts that can assist them. In fact, perhaps the real lesson is we should have had rigorous isolation of the vulnerable and let the virus spread among youth. But that opportunity has passed.

Unfortunately, with the slowness of ongoing trials, helpful interventions are likely to come quickly, thus lengthening the time of isolation for them. Solutions such as medications, vaccines, and antibodies from all of the individuals with herd immunity must be carefully tested, lest we find that the treatment is worse than the virus (unless death is likely). If that works, then we should both be able to let them get exposed and to rescue the older individuals with antibodies (from the safe members of the herd) that supplement their own response to the virus. The alternative for them is to remain isolated forever; my guess is most will be willing to take the chance.

It's important to remember that if an individual does not or can not generate enough of an immune response, then they will remain at risk of the illness forever, and deaths may continue. Perhaps we will have a test to identify such folks. The hope is that this small proportion can be isolated compassionately with individuals who have already shown themselves to be free of the virus and unable to spread it to them. The location would have strict control over the addition of new individuals unless they are also shown to have been previously treated or immune to the virus.

The point of this article is to provide an alternative narrative of a pathway out vs. "avoid illness at all cost" and "any risk to too risky" - the narrative of the current solution. Controlling the virus through distancing alone will inevitably lead to additional cases that spark a return to distancing measures as opposed to a recognition that herd immunity is not perfect.

As we saw with the recent measles epidemic, there will continue to be occasional sporadic cases for those who are not immune. This does not mean that we need to move back into panic mode when that happens. Instead, we need to accept that there will be occasional cases. An occasional illness is sad; however, this too is unavoidable in a highly transmissible virus without any kind of treatment available. The alternative is to lock up the entire nation until no one ever gets the virus, or during each inevitable outbreak. That is simply not a strategy. It means there is an unpredictable return to chaos and severe disruption. Additional chaos potentially places the health and life of the population at a higher risk than the few lives that are at risk through breakthrough infections coming through the herd immunity.

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