From herd immunity to antibody testing to vaccines, there’s a lot of medical science in the news these days as we all keep up with the latest on the coronavirus pandemic.
NSPR’s Dave Schlom, host of Blue Dot, recently spoke with Dr. James Zimring, a professor, blood pathologist and author of “What Science Is and How it Really Works,” about some of these concepts, what they mean and why they’re important when it comes to COVID-19.
You can listen to their full conversation at the top of the page, and read highlights from the interview below. This conversation previously aired on our COVID-19 Special Program, on Friday, May 15, and Zimring also appeared on Blue Dot back in October to discuss his book.
What is herd immunity?
So when a new pathogen, and by that I mean a germ like a bacteria or a virus, enters a population, the reason you get an epidemic is that one person could infect, you know, four people, and then each of those four people can infect four people, so now you've got 16. And each of those 16 can infect four people, and so on and so forth. And you get a geometric expansion of the epidemic. But after enough people get infected and survive and are therefore immune, now, when someone is sick, a lot of the people they bump into have already been infected and can't be infected again. ... So eventually, this process of self-limiting, because so many people are immune from their previous infection, that the epidemic can no longer propagate the way it does at the beginning. And that's called herd immunity.
What types of tests are available and what do you think of them?
There's two separate issues. The first is do you actively have the virus in you right now? And the main way to test that is to test for RNA. So Coronaviruses in general, and COVID-19, in particular, use RNA as their genetic material. And there's a process called a polymerase chain reaction, which can detect just the RNA from that virus. And because this test is very specific, meaning it doesn't cross react much with other things, and so if it's a positive, and it was done properly, there was no contamination or other problems, then it's usually a true positive and it's very meaningful. ...
There's also a new test out there that's just been approved called an antigen test that tests not for the genetic material of the virus, but the intact virus itself, which also has advantages because sometimes the genetic material can hang around longer than the virus has actually been there. So that's testing for the virus itself.
Antibody testing is testing your immune response to the virus, which is basically used to tell if you've ever had an infection. And this is a much more problematic circumstance for a number of reasons. First of all, the FDA has opened the floodgates, so to speak, and are letting all the tests come onto the market without the traditional scrutiny. And I believe that was the correct decision. But we have to fix it and clean it up after the fact because we have to have the testing in place, but we need to understand how good it is. And why would antibody testing be more problematic than the genetic testing for the virus itself? Coronaviruses are very common. There are four types of Coronavirus basically caused the common cold. They're ubiquitous in the human population. Roughly 90% of people have antibodies against those Coronaviruses. And those Coronaviruses are related to COVID-19. So when you get a positive on a COVID-19 test, how do you know if that's really an antibody against COVID-19? Or if that's an antibody from a cold you had last year that is cross reacting with the COVID-19 antigens? Now, there are ways to figure this out. As we go forward, and people are trying to find unique parts of the viruses that don't overlap, but that makes the antibody testing particularly challenging.
If you’ve had COVID-19, do you become immune?
It's too early in the COVID-19 epidemic really to understand what happens over time. I mean, we're just a few months into it, regrettably. …
We have to assume that anyone who has been previously exposed and has lived has some immunity. Otherwise, they would have died from the viral infection. They did fight it off — whether the antibodies did it, or it's a cytolytic T cell response, and the antibodies just indicate that. However, how long that immunity lasts, and whether they can become reinfected or not, is unclear.
When we look at other Coronaviruses, the antibodies tend to fade much faster than we're accustomed to with other types of infections. They stick around for a couple years, but then but then they fade off. And also the virus has the capacity to mutate — not as quickly as a lot of other viruses do like influenza — but it has it and so it's kind of a competition game. So at this point, I don't think we know how long immunity lasts. But I think we can be confident that there is immunity, otherwise no one would ever recover.
Where do we stand in the vaccine effort?
Well, vaccines are awfully hard to predict. You know, there have been some great triumphs with vaccines in our history. We've eradicated smallpox, we have effective vaccines for measles, mumps, rubella, chickenpox, polio virus, etc. But I remember when I was in med school, and the HIV epidemic was just starting, we were well told, oh, we'll have a vaccine in five years and 10 years and, you know, two decades and so on and so forth. And we're still not there. So it's a bit of a gamble.
You never know if a vaccine is going to work because every virus has its own way of trying to get around the immune system, and its own particular escape mechanisms. However, I'm cautiously optimistic, if for no other reason — we've learned an awful lot of immunology in the past couple decades. And there are so many efforts simultaneously underway, that the likelihood of one of the vaccines showing at least partial efficacy, if not complete, efficacy is, in my opinion, reasonably high. Of course, that's not all that you need, it also has to be safe.
The disease is manifesting in different ways for different populations. Can you talk a little about that?
It's not uncommon for a single infectious agent to cause different manifestations that seem even shockingly different in different populations. So in the elderly, and in other groups that are vulnerable either to pre-existing conditions or other factors, as everyone I think is aware, the primary problem is the lung and here it's the ability of the lung to allow oxygen to enter your blood. And I want to make a distinction here between the infection and the disease. They are not the same thing. How your body responds to the infection often causes the disease. The cells in your lung are just as very thin little slip of cells that allows gas to exchange, and if it gets inflamed and covered with scar tissue or pus other things, the gas can't go across. That's the disease. That can be separate from the infection. But the lung illness is what is afflicting older demographics and vulnerable demographics and these are people who wind up on ventilators or even on bypass machines in extreme cases, and have a reasonable mortality rate, which has been this horrible thing that we've all been watching unfolding.
People closer to their 30s and 40s, who have a lower mortality rate, though, have been showing up in the hospital having strokes and blood clots that are indicative of an activation of their coagulation system, which can also happen when you're inflamed.
And then in children, we've begun to see rarely — but remember, if you have 350 million Americans infected, you're going to see rare things emerge — an inflammatory syndrome throughout the body that inflames the blood vessels. And it resembles a rare disease that's called Kawasaki disease, which happens in kids and can can have multisystem manifestations. A lot of the kids, many of the kids are gratefully recovering, but in extreme instances, it's resulting in death as well. And it may very well be that there's also rare manifestations of the disease that we haven't seen or haven't appreciated in other subgroups, but this is not a one-size-fits-all symptom package of COVID-19 infection, and we're learning an awful lot at a very high price as this unfolds.
How do you balance trying to live your life and being a responsible and safe citizen?
I think that it is a reasonable expectation that we should be mindful of the vulnerabilities of our fellow citizens, that when we engage in unnecessary, reckless behavior, and by that I mean ignoring social distancing, having contact in large groups when we don't need to, etc., we are not just making a decision about our own safety, we are making a decision about the safety of others and without their consent. And I think we need to be mindful of the fact that in an epidemic like this, I guess, as always, but maybe more so now, what we do matters, and we need to pay attention to the guidelines and the recommendations, because not to do so is basically a depraved indifference for your fellow citizens, if not yourself.
This interview has been edited for brevity and clarity. Click the “play” button to listen to the entire interview.