How Should I Use Rapid COVID Tests?

And why we desperately need more of them

Join me tomorrow at 10:30 a.m. ET for an AMA! I’ll try to focus on questions about kids and vaccines, and rapid testing. You’ll get an email when it starts up. Think of questions!

This AMA will be open to all, although future monthly ones will be subscriber only.  


There have been many policy failures in the management of the COVID-19 pandemic in the U.S., but I think the way we have managed testing may be the most extreme. This begins with the lack of testing early on (Scott Gottlieb’s new book has an excellent discussion of that) and has continued to the present. Both Michael Mina and David Leonhardt wrote last week in the New York Times about the policy failure to provide good access to rapid antigen tests. 

Rapid tests, at the present moment, are expensive and hard to find in the U.S.  This may be improving with the approval of a new rapid test option, and the White House saying they’ll spend a billion dollars to make tests more available. Both are pieces of great news (more at the bottom, also, about how to get tests right now). Of course, the fact that we are only now developing a plan to have more tests is a policy failure.

It’s not the only failure. Judging from the emails and questions I get, we have also failed to convey to people the value of rapid tests. If we don’t do this communication well, having more tests is of little value. 

A specific question: let’s say we do have tests in our home. How, precisely, should we be using them?

I’m going to dive into this below, with help from Dr. Michael Mina and Shawna Marino.1 I want to focus on the basics. First, an overall framework for how to think about the value of various tests (and how they work). Then, answers to some basic FAQs. A note that I’m focusing today on using these in your home or with your family rather than at school; here’s another resource focused on school-based use.  

Big picture: What are the kinds of COVID-19 tests, and why might the results be different?

There are, broadly, two types of tests that can tell you if you have COVID-19. There are what are called molecular tests, which you probably know as “PCR” tests. These look for evidence of the RNA of the virus in your system. These tests are very sensitive, in the sense that they detect even very small amounts of viral RNA; for example, they’ll often return a positive result even after your infectious period, since residual (non-infectious) viral fragments remain.

While most schools require a PCR test result to return to school, PCR tests cannot typically be run at home and require a lab. Rapid at-home molecular tests, while promising, are not widely available for home use yet, so I will refrain from discussing them here.

The second type of test is an antigen test, what we are colloquially calling a “rapid” test.  These work by looking for the virus proteins — basically, by looking for evidence of active virus. These tests are most accurate during the highly infectious period; with Delta, that’s two to five days after exposure. 

The antigen tests can be run at home, and they produce results in about 15 minutes. The output varies by test but typically looks like a pregnancy test: one line negative, two lines positive. (I’ve put an image below of a negative one, from a BinaxNOW taken on one of my children a month or two ago.) 

These two tests may produce different results, and it’s important to understand why. Obviously one reason is that there are false positives and negatives on any test, due to user error or other issues. But let’s put that aside. Even if they are used exactly right, you may get a negative rapid test and a positive PCR test. In fact, this is expected to happen. Why? 

Broadly, this occurs because the PCR test is more sensitive to lower viral loads than the rapid test. For example, if you’ve recovered from COVID, the PCR will remain positive for a while — for weeks or, in rare cases, months — while antigen tests are negative. Importantly in that case, though, you are not contagious anymore. The antigen test in that case is “right” in the sense that you shouldn’t worry about spreading to other people. 

More generally, a positive PCR with a negative rapid test suggests a low viral load, one that is much less likely to imply contagiousness. This is why people sometimes talk about antigen tests as “contagiousness” tests. 

Is one of these tests better? I’d argue no; that they are useful for different purposes. The rapid tests are fast, easy to run, cheap, and can be used at home. They are excellent at picking up on infectious people. A PCR test is more definitive as a test of whether a particular individual has been infected with SARS-CoV-2, the virus that causes COVID-19. But since most PCR tests are done in a lab, they take, typically, two to four days to get a result and (as noted) they can be positive even if you’ve stopped being contagious weeks earlier.  

In a sense, which test is “better” is all about the use case. Which I turn to below. 

Big picture: What is the general use case for rapid tests?

Rapid tests do a very good job of picking up COVID when people are highly infectious, whether they are symptomatic, pre-symptomatic, or asymptomatic but with an infectious viral load. If you know when you were exposed, this infectious period is usually two to five days after exposure. They are also easy and fast, and you can use them in your home or on the go, even daily if needed. 

This means the use case for rapid tests is:

  • Immediate testing when people have symptoms

  • Testing after a possible exposure

  • Asymptomatic screening to keep schools and businesses safe (I won’t talk much about this here since we’re focusing on your family use, but see more on the policy side here)

The first of these is fairly obvious. The best reason to have rapid tests around your house is to test family members if they have possible symptoms. The rapid tests are highly accurate during an individual’s most infectious state, which is typically when your body starts showing symptoms, so in this case you’re likely to find out if it is COVID.

The second bullet here is a little more complicated. Basically, rapid tests can be very helpful in testing if you think someone might have COVID and may not yet be showing symptoms. One example of this is if there is a known exposure. This is the idea behind school “test-to-stay” programs, which allow students to stay at school after an in-school exposure but require them to take a rapid test every day for a week. In this protocol, the rapid test would effectively pick up a case in its presymptomatic phase. A large randomized trial in the U.K. has shown that such a protocol is preferable to quarantine in terms of keeping kids in school and does not result in more COVID-19 transmission. 

This use case also applies to things like work travel or getting together with a lot of people who you do not normally see. In these situations, exposure is more likely. It’s not necessarily that you know you’ll be exposed, but if you interact with 300 people at a work conference, or you bring 20 people together at an extended family dinner, it’s just more likely that an exposure could happen. Testing before you enter these situations or after you’ve participated and before you spend time with unvaccinated children or more vulnerable older adults is a layer of protection: as Shawna Marino put it to me, “It’s like sunscreen.”  

There are also cases where you just want to be more careful, like going to see an immune-compromised relative, or someone in a nursing home. Rapid testing in that situation — even if you do not think you’ve been exposed — may well make sense. 

Whether you want to use a rapid test in these situations is going to depend a bit on your risk tolerance and home situation. If you’re coming back from a work trip to a house of fully vaccinated people, post-travel testing will make less sense than if you have unvaccinated kids. 

Two other notes. First: Most of the over-the-counter approved rapid tests come in boxes of two. This is technically because the FDA wants us to use two tests in a given period of time (usually 36 hours) to rule out any case where we didn’t have a high enough viral load to indicate “positive” the first time. Sometimes it takes longer for COVID-19 to register in your body, so if you take a test two days after potential exposure and it’s negative, it’s recommended that you take a second test another 24 to 36 hours afterward to be certain that you are truly negative.

Second: If you do not use these all the time, doing so for the first time can be intimidating. It shouldn’t be! The tests are easy to use and your kids will get used to it fast. If you want a little help, this video guide might work!

That’s a broad framework — maybe it’s enough to answer your questions! — but let’s do a few specific questions that are on many of our minds.

FAQs, rapid test edition:

My kid woke up with a runny nose and a slight cough. Should I test him?

Yes. This is the best reason to have the tests around the house. If it is positive, follow up with a PCR. 

If it is negative, I will leave to you the question of whether the school rules permit the child to go to school with a garden-variety cold. I will provide you this tidbit from Shawna, though:

I learned this past week with my own two kids who got colds that masking and runny noses don’t mix. My 15-month-old stayed home from daycare for three days with a runny nose, no fever, and negative rapid antigen tests, because I didn’t want her to give her cold to smaller babies. My 5-year-old went to school all week with no cold symptoms, but because my daughter was home, I tested him daily using rapid tests just to be sure. By Friday, he had a bad runny nose too but no other symptoms. He technically was allowed to go to school, but he couldn’t blow his nose without removing his mask, and any sneeze resulted in a disgusting booger-filled mask. Now we know it may be best (or necessary) to keep kids home if they have a runny nose (which is so, so hard for working parents…) because masking and runny noses don’t mix!

I want to see my (vaccinated/unvaccinated) family at an indoor gathering; we do not plan to wear masks. There are some unvaccinated kids (or unvaccinated adults). What should we do?

Looking at the framework above, this falls into the “possible exposure” reason to test. Even if no one thinks they’ve been exposed, it’s hard to know, and getting a bunch of people together increases the risk of one unknown exposure. 

So: 

  • Rapid-test everyone before getting together.

  • If multiple days, consider testing again (possibly multiple times, depending on test availability and risk tolerance) during the gathering.  

The dependency in the second bullet is important here. In a world of inexpensive and widely available rapid tests, I’d favor testing a bunch of times during a multi-day visit. Given the actual availability and cost situation, this isn’t likely to be very feasible. Because of that, the first bullet is the most crucial. Test before getting together. But remember that if people traveled to get there, it’s important to test a few days after arrival too.

Broad scenario: I’m going on a work trip and I will return to unvaccinated kids. Should I test when I return, and when?

Again, this falls in the “possible exposure” group. If you have symptoms, of course you test. Without symptoms, testing would be intended to pick up a possible exposure. The “ideal” would be to test daily until five to seven days post-travel. This isn’t likely to be feasible for most people, but some testing a couple days after traveling may be. Also, some employers are allowing employees to expense rapid test costs, so that is worth asking about. 

Some people will read this and say some version of: Kids are low-risk, all the adults are vaccinated, what’s the big deal here? For me, the answer is really about the kids and school, both their own need to quarantine and the risk that they spread to other kids and out from there. I do not want to be the index case for my children’s classroom to close, or for one of their friends to give COVID to an immune-compromised parent. 

Once my kids are vaccinated, I will see things differently (Halloween! I’m holding out hope).

Can I use them on kids under 2? 

My kids are 10 and 6. At this point, they test like pros, can swab themselves, and accept it as a part of life. So I’m relying on Shawna, below, as she has a bit more experience. 

Yes — however, the instructions for use vary, and the official guides may discourage it. This is because they assume parents don’t know how far to stick the swab and don’t want to damage the nasal passage. I use them on my daughter and have since she was about 12 months old. Virus is virus, and they will work if you can get a good sample. My trick: She sits in a comfy chair and I take out the swab and pretend to tickle her nose — almost a combination between the airplane eating trick and a tickling game. She laughs and it’s over before she knows it. As someone who has used the NoseFrida on both my kids, taking a nasal sample is a piece of cake compared to sucking out boogers. 

For kids older than 3, we strongly recommend letting them take the nasal sample themselves. It’s glorified nose picking. Make them count to five on each side. “Big circles. Can you tickle yourself? How much booger can you capture in there? I don’t see any boogers — get it all on there!” We made it goofy with my son early on and also got him interested in the testing steps after. He knows to look for one line, and now that we test at home frequently, he has been a champ with his mandatory weekly school testing too. I am a firm believer that if the parents are calm and easygoing about testing, the child will not be anxious or worried. Make it fun, show them that you do it too (just like masking), and their resilience will easily kick in! 

I got a positive on the rapid test for my kid. WHAT DO I DO?

Don’t panic! First, now that there are a few different brands of over-the-counter rapid tests, it’s worth using another brand right away as a follow-up. These rapid tests do sometimes pull up false positives; it’s not that common, but it can happen (my kid had one last summer). The fastest way to double-check is to use a second rapid test. If that’s positive, follow up with a PCR at your doctor, a pharmacy, or a state testing site. If the second rapid is negative, you could also follow up with a PCR, if you want to be totally certain. 

If the PCR is positive, your kid has COVID. Isolate them and follow instructions about quarantine for any other close contacts. 

If the follow-up PCR is negative, then it was a false positive. Until next time…

Where can I get these, and how can we get more around?

Throughout the entire pandemic, many folks have asked: Why isn’t all COVID testing free? As the op-eds at the top point out, COVID testing is a public good, and we should be trying to flood the system with rapid tests so that anyone can access them at any time for free. This is what the U.K., Germany, and other countries have done. The Biden Administration announcement yesterday was a step forward, but there should be much more investment. If you want to advocate for free rapid testing, the RapidTests.org group has a great webpage that allows you to customize a form letter and send it to your members of Congress: https://www.rapidtests.org/take-action. Dr. Mina’s team, along with many other public health experts, are actively working with the Biden administration to change policy, but demonstrating grassroots support is always helpful. Notably, in response to increased demand, the FDA has just authorized another at-home test, price to be determined.

In the meantime, if you want to get the tests…

  • Walmart has the cheapest options, though they are not always in stock.

  • CVS and Walgreens also offer them, though they are not always in stock (sensing a pattern?).

  • Call your local public health department and ask if they have any at-home rapid tests for residents. Some states have bulk supply and distribute them at local libraries or community centers. 

So much of my writing over the past year has been about frameworks, risk tolerance, and, frankly, learning to live with uncertainty and take control where we can find it. Rapid tests are basically a way to take back a little control. A way to feel better about doing more, about having playdates and birthday parties and just getting out. The problem, obviously, is that we need them to be cheaper. Or free! And available everywhere so people can access them.

Increased consumer demand, and more production, will help. But I also hope the government steps up. I’d like to see every household in America get a shipment of rapid tests in time for Thanksgiving - in fact, this was the plan Dr. Mina called for a year ago.  It doesn’t seem like too much to ask. 


Did You Miss It?

1

Content for this piece was provided by Dr. Michael Mina, MD, Ph.D., an assistant professor of epidemiology and immunology at the Harvard T.H. Chan School of Public Health, in partnership with Shawna Marino, MPP, who has been working with Dr. Mina on public health policy and communications for the past year. Shawna is a mom to two children under five and also leads strategic communications for Detect, a new health technology company that’s developing a rapid molecular test. Dr. Mina has been one of the world’s leading advocates of rapid testing, and his work has informed policies around the globe, including national rapid testing plans in the U.K. and Europe. He and his team have been working closely with the Biden administration on a national rapid testing program for the U.S., detailed in the New York Times last week.