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The CDC Now Recommends: Read The Fine Print

Updated: Jan 18



A question that I am hearing a lot lately is some version of this, “If you get COVID-19, the CDC now says a ten-day isolation is no longer needed and that five days are sufficient. Is that really enough?!”. It’s led to a series of hugely popular memes, like this one, based on the theme of: “The CDC now says / The CDC recommends”.

Despite loving all the creative memes, as an epidemiologist I support the CDC’s decision to issue this change in guidance. They have arrived at an imperfect solution to a difficult and nuanced problem.


Still, it’s a substantial change and it’s reasonable to wonder:

  • Did the science change?

  • Is this five-day rule safe for me/my family/ my employees?

  • What should the isolation policy “really” be?


The key to better understanding this new policy is reading the fine print.

Unfortunately, a lot of the fine print is getting missed.


It is the job of the CDC to deliver clear, well-explained responses to deal with questions and reasonable concerns that have arisen in the context of this new and dramatically different recommendation. And it is expected that as the science of COVID-19 evolves, recommendations about how we mitigate risk will change. With more data on COVID-19 transmission, we can tighten the isolation period to focus on a time when people are most likely to be infectious. But don’t forget the fine print. This recommendation clearly states that this is not just a five-day isolation period but rather a five-day isolation period under specific conditions. The caveats are critical.


If the new guidelines were fully understood and followed as written, I think most Americans would feel they are reasonable, evidence-based, and mitigate—but do not eliminate—COVID transmission risk.



Specifically, to end isolation after five days, an individual should:

  • Avoid traveling until ten days have passed.

  • Be fever-free for 24 hours. Even if your temperature returns to normal on day five, you cannot end isolation until a full 24 hours after your fever breaks. And remember, all temperatures should be taken without the use of medications (acetaminophen, ibuprofen, etc.) that may mask a fever.

  • Isolate yourself for at least five days. This means knowing when to start counting days, so let’s review: Day 0 is (a) the day you first have symptoms or (b) if you have no symptoms, it’s the day you were swabbed for a test that later comes back positive. Let’s say you develop a sore throat on Monday and get tested that day and it comes back positive. Monday (the first day of your symptoms) is day 0, so start counting your isolation days on Tuesday (day 1) and remain isolated through Saturday (day 5). You are free to end your isolation on Sunday if you are symptom and fever free (for at least 24 hours) and will wear a mask in all public settings through the following Thursday.

  • Be symptom free. Specifically, the CDC states: “If you have no symptoms or your symptoms* are resolving after 5 days, you can leave your house.” Overall, I agree with the CDC’s guidance here but dislike the vague term “symptoms are resolving”. It is my least favorite part of the guidance since one person’s resolving symptoms are another person’s sick day. In my opinion, wherever possible, anyone with lingering symptoms should stay home until they are symptom-free. Symptoms matter! In fact, during the 1918 Flu, aka “The Great Influenza”, the US government coined the phrase, “Coughs and Sneezes Spread Diseases”. Over 100 years later, it’s still good public health guidance.

  • Wear a mask indoors whenever you’re inside any building other than your home. This means avoiding restaurants and lunchrooms and any settings where masking is not possible. And, for me, this guidance also goes a long way towards protecting against the vagueness of “resolving” symptoms. As discussed previously, wearing a robust mask protects the mask wearer and others in their vicinity. If you have not already, it makes sense to up your masking game. CDC just updated its masking guidance to push for stronger respiratory protections since all masks are not created equally (learn more here).


Below I address some common questions:

  • What if someone does not follow this guidance and leaves isolation without wearing a mask or while still feverish?

Surely, that can and will happen. But it has been happening all along. Not everyone adhered to longer isolation recommendations. Those who follow the new policy as written are very unlikely to expose others (though there will be exceptions, there always are!). And for those who opt not to follow CDC guidelines (now or in the past), a policy change is not likely to have any impact.

  • Why not test out of isolation?

This is a good question. And the answer is two-fold:


First,...have you tried to get a COVID test lately?! Asking people to do the impossible is not good public health policy. In some ways asking people to isolate themselves for ten days, to miss work, school, etc. was also not good public health policy when most felt well and were no longer contagious after a week. There is risk elimination and risk mitigation—this policy of leaving isolation after five days with a mask but without a test is the latter. As part of risk mitigation, testing out was likely considered by the CDC and in an ideal world would be used but we are not living in that world. Still, if you can access a (lateral flow / rapid antigen) test, you should use it before ending isolation.


Second, antigen tests do a great job of picking up contagious infections as discussed previously, but nucleotide-based tests (like PCR) are highly sensitive tests that amplify viral material and may pick up inactive viral “debris” remaining after an infection. That debris is not itself infective but rather represents a prior infection that has been cleared and is no longer transmissible (illustrated here). Be careful about what test you use at the end of a COVID-19 infection since using a nucleotide-based test could yield a positive test result that is inaccurately interpreted as a need to isolate at home even when you are not ill or contagious.


The best approach, if you can access an antigen rapid test, is to test at the end of your five-day isolation period. But only if you are fever-free for 24 hours without the use of fever-reducing medication and your other symptoms* have resolved. Otherwise, it is my opinion that it makes sense to wait until those conditions (fever-free and symptom free) are present to run the test. A negative result should give you extra confidence in the decision to end isolation—but beware: while unlikely, it is still possible that you are infectious so wear that robust mask until you hit the ten-day mark!

  • Why should I work so hard to avoid Omicron? If this variant is less likely to send me to the hospital, more likely to infect me, and I don’t need to isolate for long - I mean, aren’t we trying to get better population immunity?

It’s important to acknowledge that working hard to avoid infection does guarantee protection from a highly infectious virus. You might get it despite your best efforts. However, it is not advisable to try to get this infection or to let you guard down.



Here are some reasons to keep up the fight:

  • There is a risk of both acute and chronic disease.

We have evidence that acute Omicron is a milder illness, and compared to prior variants, is less likely to hang out in the lungs and less likely to cause hospitalization and death. But sick is sick, and being sick is never fun. Should you be unlucky enough to have a more serious illness with Omicron, this is a particularly bad time to be treated as we run low on COVID-19 treatments and personnel in our overtaxed health care system.


Another concern is that we lack an understanding of Omicron’s long-term impact. Will Omicron lead to Long COVID? We do know from previous variants that it is not unusual for Long COVID to start out as a mild infection, not requiring medical attention, so it would not be surprising if that is also true of Omicron.


It is also possible that like other viruses, Omicron could go dormant only to re-emerge later in life. We are familiar with viruses that already behave in this manner such as the viruses that cause herpes, polio, chicken pox, and mononucleosis. The viruses that cause those diseases are neurotropic, meaning they can infect and hide out in nerve cells only to emerge at a later time. There is good evidence that SARS-CoV-2, the virus that causes COVID-19, is also neurotropic.


  • Immunity to Omicron may or may not translate to immunity from other variants.

While it is possible, even likely, that Omicron will offer some protection against other variants of SARS-CoV-2, we do not yet know this to be true or, if true, how much or how durable the protection will be. It’s not a good reason to let your guard down.


  • Because we need to look out for our hospitals and the people who work in them.

Yes, if you get Omicron, it will probably be mild, and you may not need medical help and will potentially be back at work soon. But some portion of those with Omicron will end up in the hospital. Even a tiny, tiny proportion of those infected could be a very large number of people given the staggeringly high number of infections coming in such a short period of time. It’s less about any one of us getting Omicron than all of us getting Omicron at the same time.


For hospitals to be ready for those who have severe Omicron or something entirely unrelated (e.g., appendicitis), there must be enough beds, doctors, and nurses to keep the system not just running, but functioning well. Not only is there the risk of running out of room to treat emergent medical needs but there is strong evidence that overwhelmed hospitals reach “tipping points” beyond which the likelihood of mistakes increases.


  • Because we need to protect those who have little to no protection.

No one wants to be the person who inadvertently brings COVID-19 to someone with cancer, or any other condition that makes it challenging to build protection from this virus even with vaccines. Every transmission can start a chain of new infections that has the potential to reach someone vulnerable to severe COVID-19.


  • Because we need you back at work or school!

Most workplaces have contingency plans for a small fraction of workers being out on any given day. But with Omicron, we have seen absence rates of 20% or more. You may be a teacher, truck driver, grocery store stocker, airline flight attendant, or almost anything else that keeps our society up and running and we need you.


Please continue to try to avoid COVID-19 by taking reasonable, feasible precautions. If you do get it, isolate for at least five days and until you are symptom-free and at least a day past a fever. And if you can find a test, take an antigen (not nucleotide-based) test after five days, 24 hours after any fever, and once all symptoms have passed.


Should you find yourself sick with COVID-19, be sure to remember:

  • Give yourself grace. Even the most vigilant among us can fall prey to a wildly transmissible virus.

  • It is not a race (to end isolation). If you are still coughing or had a fever yesterday, it’s not time to leave home.

  • Cover your face (with a robust mask!) until you are at least ten days past the start of your infection.



*Symptoms like loss of taste and smell can linger for weeks or longer and should not be part of the decision to end isolation. All other symptoms (cough cold, and any other listed here) should be considered.





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