Yesterday at a town hall style forum the president of the United States once again asserted an opinion regarding Covid 19; that the virus would just go away on its own, an opinion that the president has voiced repeatedly since the start of the pandemic. This time however he specified that the mechanism by which the virus would cease to be a concern was through herd immunity, or the idea that eventually a large enough percentage of the population would have contracted the virus and through exposure built a natural immunity to it, to stop the virus from being able to effectively spread through the population. While herd immunity is an actual phenomena and could prevent the virus from being able to effectively spread, according to the Mayo Clinic in order to have effective herd immunity, at least 70% of the population would have to have contracted and become immune to the virus. So, the question to evaluate this statement becomes; are we close enough to that threshold right now to justify the head of the current administration’s position of unconcern and inaction?

Several months ago I published my rough estimates for how many people in the U.S. may have likely contracted Covid at that time given our comprehensive lack of random testing, and the assumption that most of those who have been tested did so out of a need for medical help. I was able to use simulation techniques to create an estimate of the number of unreported cases based on the official figure derived from actual testing, which added together, gives us an idea of the how much Covid has actually spread. For anyone interested in taking a look at the original post, I’ll include a link to it here, but the gist of it is that simulation shows that for every 100 positive cases identified through testing, roughly another 121 positive cases go unreported. Today I’m using these findings with up-to-date official figures to estimate, today, what proportion of our population has likely been infected and measuring that against the 70% threshold needed to achieve herd immunity.

As of this writing on September 15th, the current positive Covid case tally in the U.S. is 6,711,606. Using the assumptions that most likely fit what we have observed about who will and will not need to be tested, simulation tells us that in reality around 14.8 million people in the U.S. have actually contracted the virus. To put this into perspective, the current U.S. population is around 328.2 million; to date this would put about the proportion of the population that has likely been infected at about 4.5%.

Now to give this herd immunity the benefit of the doubt, I have re-run my simulation using more severe assumptions about the number of people who get tested out of every hundred that actually contract the virus, in other words, I assume that less people need to get tested, because less of the people who are in a high risk category actually end up having severe enough symptoms to be hospitalized. When I re-simulate the data under these different assumptions, I find that best case (if you want to look at more people being infected as a best case) 23-24 out of every hundred infected ends up getting tested, meaning for every hundred reported cases another 319 cases go under the radar. This would mean that to date there would actually have been a theoretical 28.1 million infectees in the U.S., roughly 8.6% of the total population.

Even at this estimate we are far from achieving the 70% threshold for seeing herd immunity.  If the virus continues to spread at the same rate that it has over the last 7 months, it would take another 86 months, or seven years to reach a natural level of herd immunity, and assuming that the death rate stays the same, we would see the total number of Covid deaths in the U.S. surpass 2.4 million. So, to say that we should do nothing and let the virus run its course and disappear when it has spread far enough to give us herd immunity seems like an imprudent policy to say the least.

There is one caveat here, and that is the other method of obtaining herd immunity – through vaccination. It will definitely not take seven years to develop an effective vaccine, so really this simulation just makes the point that we will not see the virus “just go away” through the mechanism of herd immunity before an effective vaccine is developed.

However, the idea that a vaccine will eventually come does not mean that we should just ignore the risk of viral spread before that point comes as the current administration has attempted to do, and in fact urged the rest of us to do. The more we allow the virus to spread unabated prior (or even after) the introduction of a vaccine, the more opportunity we give the virus to mutate in ways that could make it either more deadly or that could make a vaccine developed for the current strain of the virus less effective. We also cannot assume that a vaccine would solve our problems overnight. Having a vaccine available will certainly help us get to a point of herd immunity faster, but the challenges of producing and distributing it to the over 60% of the population needed to supplement what immunity may be already present is not a small on and getting enough of the population inoculated through vaccines will likely take time as well.

To sum up, herd immunity without a vaccine in place will not come any time soon and even with vaccination may take time to set in. Furthermore a lack of mindfulness about the spread of the virus also gives is all the more opportunity to mutate and invalidate whatever progress we do make towards achieving herd immunity whether through exposure or vaccination.

I think it is evident that what the president is trying to accomplish by ignoring the virus is to get the economy back to a place of normalcy as the economy has been one of this administrations favorite benchmarks for success throughout the last four years. The fact of the matter is, until we actually effectively address Covid and make it safe for everyone to participate in that economy again, we just aren’t going to see a full economic recovery, there are too many of us who will have to sit out on the sidelines because pre-existing health conditions mean that risks can’t be taken. If we don’t want to hobble our economy and exclude some altogether I’m afraid we’re going to have to start taking the virus seriously and do more to slow the spread. Whether we want a healthy population or a healthy economy, we can’t afford to simply wait for the virus to just go away.

I conducted the analysis behind this post using Python with reference information from the Mayo Clinic, see link in article. To view the python code that I used to create my simulation estimates, check out the project on GitHub.