As we approach the anniversary of the worst pandemic in a century “pandemic fatigue” is becoming a serious problem. This is more than just being tired of dealing with the changes to daily routine, there can be serious economic and even health consequences to the steps taken to stem the pandemic. Treatments are coming online, and our management of COVID-19 illness is slowly improving over time. But the daily new cases worldwide is still increasing, and deaths remain high and steady.

The reasonable question on everyone’s mind is – when will this end? Also, how do we make it end more quickly? Aggressive measures to “flatten the curve” have largely worked, but in many areas they mostly delayed infections. Successful countries have managed to return to some semblance of normal, but nowhere is the pandemic gone.

So what will it take to end this pandemic? Perhaps it won’t end, and the SARS-CoV-2 virus will become endemic in the human population, like the flu. It will simply wax and wane and circulate around the world. An effective vaccine with high uptake is clearly the best option. Through vaccination we can achieve herd immunity and shut down circulation of the virus. This will probably not eradicate it, but can keep the spread limited to levels that would not be disruptive. This, I think, is the most likely option – but we are still waiting for a vaccine to be proven safe and effective, get approval, and then be widely distributed. Optimistically this can happen by the end of 2021, but I stress that is optimistic.

What about natural herd immunity? This strategy is essentially to let the virus circulate, and after enough people have caught the virus and survived there will be enough resistance to reduce spread and the pandemic will end. This option is occasionally floated by politicians, and even some fringe scientists, but has been repeatedly criticized by the majority of experts.

Recently the World Health Organization stated that the goal of achieving natural herd immunity is both unscientific and unethical. They made this statement partly in response to President Trump and others stating that we may achieve natural herd immunity. How plausible in natural herd immunity and what would it entail?

The short answer is – we don’t know, but it isn’t looking good. We simply do not know enough yet about this novel virus. Pertinent questions include: how effective is the immunity that results from infection and (this is critical) how long does it last? How much of an infection is necessary to trigger immunity? Will asymptomatic cases be immune? And what level of immunity in the population is necessary to achieve herd immunity, given this varies for different viruses depending on how contagious and infectious it is?

We don’t really know the answer to any of these questions, but the early clues are not encouraging. Coronaviruses in general tend not to provoke lasting immunity (years), and SARS-CoV-2 may be no different. One recent study published in The Lancet, for example, found that, if you standardize to the general US population, about 9.3% of people have antibodies to SARS-CoV-2. There were regional differences that follow the density of COVID cases, with the highest regional percentage being about 25% in the Northeast (and about 35% in NY state). This number is about 10 times the number of confirmed COVID cases, so many people are being exposed to the virus without ever being diagnosed (whether or not they develop symptoms).

This number is low compared to what is needed for herd immunity, which varies from 50-90% depending on the virus. Even for the low end of the spectrum, we would need five times as many people exposed as we have now. That would probably mean about 1 million Americans dead just to reach the low end of the herd immunity range. That number could easily have to double, as COVID is highly contagious.

But also, we still don’t know how long immunity lasts. We know it lasts at least 3 months, but that is not very long. What if it lasts for a year? That is well within the range of likelihood. That would mean that most people who were previously infected would be losing their immunity long before we achieved natural herd immunity. In this scenario the virus would simply continue spreading around the world.

There are now numerous cases, although still somewhat rare, of people getting COVID for the second time (after just months). How many cases will there be of reinfection after a year or two years?

We also don’t know what the long-term effects of this illness are, and there are some early indications that people who survive a severe infection with COVID-19 may have long-term symptoms. We won’t know for years what the full toll of infection is on health, and so it is a very dangerous gamble to let people get sick just to achieve immunity. This could have profound impacts on our health care system for decades.

It is true that all pandemics eventually burn themselves out, or settle down into the background. But this is not necessarily a good thing. This is what we have with the flu, which claims between 20-60,000 US lives per year, and that is with a vaccine program. We don’t want COVID to become another permanent flu, but that is where we may end up. Keep in mind that HIV is also an ongoing pandemic, lasting decades. We don’t think of it that way because we have accepted that it exists and we deal with it.

In terms of, let’s call them “acute”, pandemics like what we currently have with COVID, it is very likely that no matter what we do eventually disease resistance will increase in the population, the population of highly susceptible people will be reduced, and the pandemic will wane. The question is – what will it take to get there? In 1918 the flu pandemic killed at least 50 million people worldwide – that is 50 times the current death toll for COVID. I don’t think anyone wants to see that before achieving some level of herd immunity.

What the WHO is essentially saying is that in getting to the end of this pandemic, or at least to an acceptable background level, the worst possible path to take is through natural herd immunity. That is the path of maximum disease and death, with many perilous unknowns. The best path right now is to continue to flatten the curve with proven methods, such as mask wearing, social distancing, good hygiene, and avoiding mass gatherings, especially inside. We also need testing and contact tracing to reduce spread. We need to keep doing all this until we have an effective vaccine and can distribute it. That is the path to herd immunity, we just need the patience to get there.


Posted by Steven Novella

Founder and currently Executive Editor of Science-Based Medicine Steven Novella, MD is an academic clinical neurologist at the Yale University School of Medicine. He is also the host and producer of the popular weekly science podcast, The Skeptics’ Guide to the Universe, and the author of the NeuroLogicaBlog, a daily blog that covers news and issues in neuroscience, but also general science, scientific skepticism, philosophy of science, critical thinking, and the intersection of science with the media and society. Dr. Novella also has produced two courses with The Great Courses, and published a book on critical thinking - also called The Skeptics Guide to the Universe.