This is a picture I took back in 2011 in Tanzania. This herd of zebras was part of the Great Migration, an annual event in the spring (their fall) when 200k zebras and 1.5 million wildebeests start moving north out of the Serengeti to chase the rains. These zebras travel together with the wildebeests and eventually get where they are going hundreds of miles away, to greener pastures. But even in herds millions strong they still lose about 15% of their numbers along the way, to predators, starvation and diseases.

So I thought the picture was good because people keep talking about the ‘herd effect’. Lots of people have asked me my opinion on this so I wanted to talk about that a bit to hopefully clear up some misconceptions. Again, my usual disclaimer—I read. I study. I practice medicine. I have opinions that you can take for what they’re worth. But I’m not an epidemiologist or immunologist. I’m not political but unfortunately politics are a big part of what is happening. However I’m going to try and stay away from all of that as much as I can

The ‘herd effect’ (as it relates to immunology, not zebras) is referring to this magical phenomenon that many hope is going to spontaneously happen as more and more people get exposed to SARS2 and develop an immunity to it. There also seems to be an underlying belief that exposing your immune system to other people is somehow going to strengthen your immunity, without getting sick first.
It doesn’t work that way, folks. I wish it did. Not unless you’ve lived in a plastic bubble your whole life.

First off, your immune system couldn’t care less and is not lessened in any way by 8 weeks of social distancing. Your immune ‘memory’, such as it is, is not decreasing because you haven’t been exposing yourself to new pathogens. (Most people are getting more sleep and eating better because they can’t eat out. So our immune systems are actually probably better now than they were. Lack of sleep and poor nutrition both have a big effect.). Our immune system is not just one thing, either. It’s probably the most complex of all our body’s systems and is basically everywhere, in the form of the cells that prevent and fight infections and even cancers.
Our immune responses are there because of all of the things we’ve been exposed to previously in our lives. These exposures have created a countless number and variety of antibodies that are circulating in our blood and lining our mucus membranes. Those antibodies don’t kill anything but flag anything entering the body that we’ve not seen before so that the immune cells can quickly kill it. If we’ve seen it, we can kill it, usually within minutes. If we haven’t seen it, it takes time to develop a response and in the meantime that pathogen can do it’s thing and runs rampant, causing lots more reproduction of itself internally and causing disease in the process.

So here is the message—-you cannot get immunity to this virus, or any other virus, unless you are exposed to it or unless you get a vaccine to it specifically.
Leaving your home and mixing with other people is not going to enhance your ability to fight it off later, not unless you get it and recover. We don’t get a herd effect for free. (While there MIGHT be some carryover partial immunity from the other coronavirus-class exposures we’ve had in the past, the response is probably weak as the surface of this virus differs enough that those responses are weak or nonexistent. But partial immunity may explain why some don’t get as sick)

Across every population studied, the behavior of the virus is pretty consistent. If you get exposed to this virus, and you are in the lucky 40%, you may be one of those that gets this infection and never gets anything. You will shed virus but you don’t get sick, though you can still infect others. (That’s a big part of what makes this virus so tricky to track. These people also aren’t getting counted very often in the ‘total infected’ numbers because they aren’t getting tested).
You also might be in another 40% that does get sick and is able to recover without help. You’re likely miserable, at home in isolation, probably coughing your brains out and weak as a kitten, but within 2 weeks it’s basically gone and you’ve made antibodies. Some are barely sick at all. But at least these symptomatic people often are getting tested, at least in our country.

However you might also be in the other 20%, that unfortunate group that needs to be hospitalized. As you know, The older you are and the more medical problems you have the higher the risk there is of this happening. And it’s a percentage of these folks, about 5-10% of the total infected, who do really poorly and end up in the ICU. And once there the numbers are pretty grim.
So if you add all those up, The people that survive this process, including all the people who never got sick, who are now out there and theoretically immune, those are the ones that will give you the ‘herd effect’ IF enough have had it.

So what’s that all mean. Lets use measles as an example. Measles is REALLY infectious. It’s virulence (how likely it is to transmit to a non-immune host) is wayyyy more than just about anything. We know from past experience that if the percentage of people immune to measles in a given population falls below about 90-92%, and someone with measles is exposed to that population, then youll likely get a measles outbreak. This happened most recently in California a few years ago, when the percentage of people refusing to vaccinate their kids put that immune percentage in the 85-88% range. The ‘herd effect’ no longer was protective enough to stop enough of the transmission and a bunch of kids got really sick. The state cracked down, people also got scared and got their kids their shots, and the percentage rose again over 92%, and the measles went away. (it never is really eradicated and there is a constant battle to keep that percentage up.)

Btw, The flu is more complicated because it changes every year. And because of that we need to get another vaccine every year. And because each year the immunology folks are basically making an educated guess as to which strains are going to be prevalent for the upcoming year before they can even start making the flu shot, sometimes they hit and sometimes they don’t. And because only about half our population gets the flu vaccine every year, coverage is much less. But that’s basically why you get ‘bad flu years’ vs years when it’s less severe. The variety of the number infected and mortality annually is a combination effect of how many people got vaccinated and how well they matched the vaccine. there is also very likely some individual immunity that carries over in people who’ve been vaccinated previously. The virus changes but the antibodies may still recognize it. So the bottom line is that it is much harder to give a ‘herd effect percentage’ for flu because it likely changes year to year and community to community. It’s probably somewhere in the 50-60% range (though even that percentage still allows for many people to still get infected).

We don’t know what percentage of people will be required to have antibodies to get a similar herd effect from SARS2. It probably won’t be as high as 92%. It’s about twice as virulent as influenza (easier to catch) but significantly less than measles. The experts think it’s likely going to need to be at least 60% of a population and probably closer to 70% at a minimum. it’s all mostly guesswork at this point though because we really don’t have reliable antibody testing and of course it’s a essentially a new infection.

But we DO know that, even in the hottest of the Hot Zones, like NYC or Milan, the antibody testing that has been done is only showing percentages of immunity in the 20s. The aircraft carrier that got infected, which of course was a closed system, had about 1000 people test positive out of 4900. That likely means a bunch of people that didn’t get sick are probably protected because 20% of the population in those places didnt have symptoms . But that is still well short of what is going to be needed to generate a herd effect to be effective. The problem is, that in the process of getting to 20%, those places maxed out their health care systems and a lot died and are still dying (the aircraft carrier is the exception. They lost one 31 year old sailor. But a ship full of 18-35 year old healthy sailors isn’t exactly representative of a normal population.). The bottom line is that even where it hit the hardest already, a lot more people are going to have to get that virus before the virus runs into the herd effect wall. In places that haven’t had it very much at all there is an even longer way to go.

This would all change with a vaccine. Once we start that process, then large numbers of people can create antibodies without having to get sick. And then the spread will slow and eventually stop when enough people no longer host it. But vaccine development for viruses is tricky. Ever heard of an HIV vaccine? How bout one for herpes? Or Dengue. Or Ebola. You haven’t because they don’t exist, and not because lots of people haven’t tried. We do have other viral vaccines (varicella, rotavirus, hepatitis B ) so it’s not like it’s never been done. And the resources being poured into this have never been matched. Billions of dollars and enormous efforts are being leveled at this process. (One good thing about this is the development of vaccines for other viruses is going to be taken to another level and we may see those come out of this as well).

So what’s my point.
1). Social distancing was never meant to fix the problem. It’s Only meant to slow the spread so that the health care system could keep up until adequate testing and eventually a vaccine is developed. So far that is working. It’s REALLY working up here.
2). Many areas of the country, including our northern Michigan little bubble, haven’t been exposed enough to create any kind of ‘herd effect’. As of today there have been 272 positive cases in all of northwest Michigan. That’s not even close to a protective percentage of recovered people.
3). I’m tired of this bullshit too. We all are. And families and businesses and local governments are going broke. But we aren’t anywhere near done with it.
And if we are going to say ‘to hell with it we’ve done this enough’ and rip off the bandaid and just go back without trying to continue to mitigate the potential effects of this we WILL get our turn in the virus mill.

However There is no question that we somehow need to start to open things up. And The way the government is doing it is a continuous source of contention and debate. Our hospital also needs to open back up so we can take care locally of all the chronically ill people up here (right now in that hospital there are 5 people admitted with Covid, one on a ventilator).
The problem is that no one knows how to do this. The devil is in the details and how much and how fast is just a complete unknown. As far as the hospital, they also don’t want to make things worse and be a source of spreading it and they also will need to be flexible enough to be able to snap back into contagion-mode very quickly.
So far, the powers-that-be (the governor and local governments) are being cautious and though you can debate their method I don’t think it’s fair to debate the motive. Everyone is bleeding from this—if this was some grand conspiracy or power grab it’s certainly a really super ugly, inefficient and expensive way to do it. (Btw I’m not wading into this debate. That’s as far as I go. I support a gradual relaxing of restrictions based on the recommendations of the state-level epidemiologists).

I’ll again remind you that Cadillac Munson hospital has about 50 beds and about 12 vents. (That number can maybe/probably/desperately be doubled with some very creative jockeying of things but not without ridiculous conditions, significant losses, and that would pretty much max us out).
That hospital is supposed to cover Wexford county (35000 people), Manistee county (25000 people), Osceola county (23000 people) and Missaukee county (15000 people) as the ‘Covid Hospital’ for the 4 counties (Grayling is the designated place for that section of I-75 counties and the TC hospital is for Grand Traverse and surrounding counties.).

So 50 beds. That’s basically what we have.
Almost 100000 people in 4 counties.
No reserve. No place else to go.
Do the math. And please remember that before you bash the people that will have to deal with that reality if, God help us, it ever comes to pass.

There are enormous social, economic and political forces pushing us to get back to ‘normal’. And let’s face it we have been at this for 49 days (that’s from the day they closed the schools)—and dammit we’re all really really sick of it.
But we need to do this extremely carefully. It needs to be done slowly. Methodically. With a constant eye on new cases. And we need to be ready to lock down again if we get another surge.
But I wanted you to understand that 1). You’re not weakening your immune systems by staying home 2). We will not get a magical herd effect without enormous numbers of lives being affected and lost (or an effective vaccine). 3). Your health care system cannot bail you out with effective treatments or even supportive care if enough people get sick quickly.

So please please please still be careful. Hopefully that man in the White House is right and the warmer weather will help dampen it. The restrictions are going to be slowly lifted and we are going to be able to start to come out of our holes. And it’s essentially going to boil down to individual choices that every family is going to have to make every day. ‘How much is ok’ is going to differ. If we use common sense though, maintain 6 feet, wear your mask, limit as much as possible close contacts and follow the rules, we can still continue to avoid a disaster up here. But if enough people ignore it we will all still be at risk. That’s the ‘anti-herd effect’.

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