Coronavirus Testing, Turnaround Times, and Immunity: What We Know

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Questions around coronavirus testing and immunity are top-of-mind as the pandemic continues to spread and potential vaccines undergo trials. Emily Martin, associate professor of Epidemiology at the University of Michigan School of Public Health, breaks down the basics of coronavirus testing and what the current data show are the potential next steps for the United States as we head toward fall and flu season..

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Martin: I hope we get to a place where the tests become easy to perform and more point-of-care. I just hope that we get to a point where you could go to a local pharmacy or a testing site and have point-of-care test - they give you a result right away. I think that would be a huge change to our ability to control things.

Speaker 1: Testing is a key measure to track and prevent further spread of the novel coronavirus. Results of testing allow medical and public health professionals to gain key insights and make important decisions about care and treatment at both an individual and population level. We wanted to explore what we've learned over the past five months of the pandemic through testing and about testing, and what current data shows are the next steps as we head toward Fall in the United States.

Hello and welcome to Population Healthy, a podcast from the University of Michigan School of Public Health. This episode is part of a series of special editions of our podcast, focusing on the ongoing coronavirus pandemic. Emily Martin is an associate professor of epidemiology and an infectious disease expert at the University of Michigan School of Public Health. Her epidemiological research builds a greater understanding of respiratory illnesses and how to identify strategies to reduce infections and transmission.

Martin: Usually when somebody talks about getting a COVID-19 test or somebody asks you to go get a COVID-19 test, they're usually talking about a virus test. So this is a test that uses usually a swab into your nose, sometimes it uses saliva, that looks for whether or not the virus is present in your body, right at that particular moment in time. You also might hear about serology tests or antibody tests because those are tests that are becoming more widely available too, and those sort of look at the opposite thing. Those look to see whether you were infected with the virus in the past, but that test result and those antibodies for that test, they don't show up for it could be weeks or even a month after you have been infected. So that's a test that’s only useful later after you've already recovered from the infection.

There are a lot of big changes and advancements going on right now in the testing space. It's not really affected much of the testing that's going on right now, but it's really gonna change testing as we look out six months from now or a year from now. One of the big advancements is doing what we need to do so that people can collect their own tests at home. And so there's been a lot of investment in trying to make either home test kits, sort of like a pregnancy test, you can take it at home and get the result at home, or doing tests where you collect the swab at home and then you can mail it into a company that would do the testing there. And some of that is being done now, just not widely, but there are some companies that will collect a swab from you at home, you mail it in and then they test it. And then there's been a lot of innovation around doing rapid tests that people can handle on their own and that can be simple enough so that somebody can just run it in their house and get a test result. That's something that we might start to see more of over the next year.

Speaker 1: Once someone takes a test for COVID-19, the timing of getting the results back can vary wildly across cities, counties, and states.

Martin: One of the things I worry about a lot when we talk about test turnaround time and about access to testing, one of the reasons why test turnaround time can get so long is because not every city has a lab that has the capacity right there to run the test. And not all tests are made so that they can be run what we call point-of-care, right, in the doctor's office. You have to take the swab and you have to send that swab, it has to travel to whatever lab is gonna test that swab. And sometimes those labs are in different states, sometimes those labs are all the way across the country. And so you're losing hours by the time it takes for that swab to hop a flight to a lab for it to be tested.

So what this means is for areas of the country and for areas of the state that are more rural, it means that your access to testing is gonna go down. You might actually be able to get access to a swab and have the swab collected, but the father that swab has to travel to get to a testing facility, the longer you're gonna have to wait for results. So this creates a huge disparity in terms of people's access to information about their own infection.

So when somebody goes to get a test and they're waiting to get the result, they can either self isolate while they wait for the result of the test, or they can go about their business and hope that they don't spread anything should they happen to be positive. Now economically, it's very difficult especially for encouraging people to get tests all the time, it's gonna be very difficult to ask people not to go to work if they don't have enough time off of work to call in just because you're waiting for a test result. That's a really big ask for people to do. So we have to try to get these tests back to people quickly. There's a lot of areas in the country where it takes a week to get the test results back to people, and so that puts people in this position of not knowing whether or not they're positive but maybe they aren't in an economic position where they're able to make the choice to stay home. And so that's one of the hardest things about controlling the virus, is getting that information to people quickly, but then also supporting people so that they can stay home either when they're not sure if they're infected or even once they find out that they might be infected.

Speaker 1: We know the importance of the data from testing, but how many tests should we be conducting across the United States?

Martin: Everybody wants a magic number for how many tests are the right number of tests to be able to control the epidemic. The problem is, the right number of tests is more and as many as we need. It’s just not really a magic number that's gonna solve it. And one of the reasons for that is because right now in the summer, there's a lot of social distancing, people are keeping their space from each other, it's nice out, we can be outside and move around, but when we get into the fall and other viruses come around and cold and flu season starts, we're gonna have to test all of those people that are symptomatic even if it's caused by rhinovirus or flu or all of these other things. And so the number of tests that we need available to be responsive to these types of things is gonna change throughout the year. So we know that we need more tests, we know that we need better access to tests, and we know that we don't have enough. When will we be able to say, “yeah, we have enough now”? It's an open book so far to being able to figure that out.

One of the things that impacts our ability to control the epidemic is both access to tests for people and for people to be able to get tests if they're just mildly symptomatic or maybe they've been exposed and I don't even show symptoms yet. The other thing is, for there to be enough tests and enough capacity in the system to get people their results back in a couple of days. So you get a test and it's taking you 7 days or 10 days to find out what happened from the test, then that's not useful information for you. That doesn't help you kind of guide your day-to-day life. So when we think about enough tests, people try to solve this problem by saying, “well, do we get more swabs or do we get more labels or more like the liquid that the swab goes into?” and actually what we need is a bigger infrastructure kind of on a national scale. We need more machines and more laboratories and more well-trained people, and such is a supply chain issue. It's sort of the whole process of running the tests and then communicating the results back to people effectively.

Speaker 1: New data insights are helping public health professionals address lingering questions. If someone contracts COVID-19, how long are they contagious, how long do they need to quarantine away from others, and what might immunity to the virus actually be like going forward?

Martin: We know at this point in time that most people that get infected make antibodies. This seems to be more true for people that are infected and show symptoms than people who are infected and don't show symptoms. So if you get infected and you show symptoms, most people are making antibodies to that based on antibody tests. The big open question is we don't know how long those antibodies stick around for. So for most respiratory viruses, those antibodies will wear off over time. We don't know how long they last for this one. And some of that we can't possibly know because people just haven't been infected for that long. Nobody's been infected for two years, so we don't know if antibodies can last for two years because nobody's had antibodies for that long. We can't look. So we're continuing to learn more about the duration of antibodies as people go further and further out from infections that happened like in March or in April.

Now, the second big question is trying to figure out what those antibodies mean. Now, there is no reason to suspect that antibodies won’t protect you against a future infection because they do in many other cases. And the virus doesn’t shift and change in its genetics the way influenza does - so making antibodies to one strain may miss another strain with influenza - we don't see that pattern emerging with coronavirus. That being said, we haven't tried it. And so it's still too early to say how much antibody is needed to protect you and what types of antibodies are needed to protect you.

For me, the biggest concern right now is we don't know how long antibodies last, and that's very important both for vaccine development but also for thinking about what to expect a year from now. Can we expect that all the people that are getting infected now are just good to go next year, or do we need to be concerned about then moving back into a population where they need to be worried about being infected again?

So there have been more studies lately that have found that the further that you get out from your initial symptoms, that test result, that RNA that's being picked up, is not RNA that's being picked up from a live virus. It's RNA that's being picked up from either defective or partial viruses that are still hanging around. If you were to take that virus and try to infect a cell culture from there, it wouldn't grow. And so people are doing more and more of these studies now and finding that very few people, it can happen, but very few people are positive with infectious virus weeks after their symptoms go away.

This is something we've known to be true about respiratory viruses for a long time. That once you have a respiratory virus, sometimes it's possible to pick up the RNA or the DNA from that virus, and coronaviruses in this case is a RNA, for a long time after they're infected. And it's always been a little bit of a debate in the infectious disease field about whether or not those later detections were actually picking up virus that has the ability to transmit and infect somebody else. And it was actually kind of an academic debate that happened for a long time before this current situation now, suddenly it is incredibly important.

So on the basis of this and some other data, actually CDC has recently just changed the recommendation that if you are 10 days out from when your symptoms started and if your fever has been gone for a few days, that you're okay to go back and interact with people. Because any results the test is picking up at that point, if you're not showing any new symptoms, the results the test is picking up is just left over virus, it’s hanging around and is still being shed by your body.

As a country, we have to make it palatable for people to stay home when they're sick or to stay home if they worry that they might have been exposed or any of these other situations where you wanna limit your contact with other people, or if you're high risk and you're worried about getting infected. The sick leave policies across the country are pretty flimsy. And our ability to support people to take care of themselves when they're sick, it's not very strong in the US. And so that's I think one of our major points of focus going forward. I think in the US, we're used to working when we're symptomatic and that's not gonna be acceptable this year, even when we get into cold and flu season, and I think we have to rethink as a society how we think about people and sick people’s sort of right to stay home and recover and not infect other people. This whole scenario is going to get a lot more complex when cold and flu season starts. Things are relatively easy right now in the summer when we don't have any other viruses to contend with, but the job of tracking the virus and then figure out what to do if you personally have congestion or a cough or shortness of breath is gonna get more complicated when there are more things around that causes symptoms. And so I think that everybody needs to be thinking proactively now ahead to the fall. To think about how do we as a society, and then maybe you're an employer or maybe your manager of people at work, or maybe you’re a teacher with students, how do we interact with people that have symptoms that need to stay home and care for themselves and how are we gonna think ahead of time about doing that better? We need to think about how to take care of each other this fall.

Speaker 1: This has been a special edition of Population Healthy, a podcast from the University of Michigan School of Public Health. During the ongoing coronavirus pandemic, we’ll work to bring you analysis from our community of experts to help you understand what this public health crisis means for you. To stay up-to-date in between special edition episodes, be sure to check out our website, subscribe to our Population Healthy newsletter at and follow us on Twitter, Instagram, and Facebook @umichsph.


In This Episode

Emily MartinEmily Martin

Associate Professor of Epidemiology at the University of Michigan School of Public Health

Emily Martin is an Associate Professor of Epidemiology at the University of Michigan School of Public Health. Her research focuses on respiratory virus epidemiology, hospital epidemiology, infection prevention, and molecular epidemiology. She also leads The Martin Lab, a team of researchers at the School of Public Health whose objectives include the use of molecular epidemiology to characterize the spread and persistence of viral infections and the evaluation of vaccination to reduce the burden of respiratory infections. Learn more.