Aug 15, 2020
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The Centers for Disease Control and Prevention (CDC) didn’t exactly say whether or how long you may remain immune to the Covid-19 coronavirus after recovering from an infection. But a new addition to the CDC’s “When to Quarantine” web site did say something interesting:
“People who have tested positive for COVID-19 do not need to quarantine or get tested again for up to 3 months as long as they do not develop symptoms again.”
Hmm. Why wouldn’t you need to quarantine or get tested again? Isn’t re-infection with the virus a possibility? Or could you have that magical word that begins with the letter “I” and rhymes with the phrase “hot dog eating community”? In other words, is the CDC now suggesting that you may have immunity to the virus for up to three months after getting infected? Well, that’s certainly one way of interpreting the statement. For example, here is a tweet response to this updated CDC guidance:
So looks like you don’t have to go through that wonderful cotton-swab-way-up-your-nose experience for the three months after you’ve recovered from Covid-19, right? Maybe. Possibly. Perhaps. Read a little bit further on the CDC website, like one sentence further, and you’ll see the following:
“People who develop symptoms again within 3 months of their first bout of COVID-19 may need to be tested again if there is no other cause identified for their symptoms.”
So you may have immunity for up to three months, unless, of course, you don’t have immunity for that long. Seems like that statement has the certainty of saying, “I love you until, of course, someone else better comes along,” right? Maybe, perhaps. Possibly. Well, not exactly.
Even though those on social media seemed to take the relatively new statements on the CDC’s website (apparently these statement were added on August 3) as a statement about immunity, an August 14 CDC media release suggested otherwise. This release was entitled, “Updated Isolation Guidance Does Not Imply Immunity to COVID-19.” Take a wild guess as to what this media release said.
Here is how the release began: “On August 3, 2020, CDC updated its isolation guidance based on the latest science about COVID-19 showing that people can continue to test positive for up to 3 months after diagnosis and not be infectious to others.” The media release continued by saying, “Contrary to media reporting today, this science does not imply a person is immune to reinfection with SARS-CoV-2, the virus that causes COVID-19, in the 3 months following infection.”
So what does the updated guidance really mean? The CDC release added that “The latest data simply suggests that retesting someone in the 3 months following initial infection is not necessary unless that person is exhibiting the symptoms of COVID-19 and the symptoms cannot be associated with another illness.”
Looks like then the CDC didn’t really make a statement about immunity to the Covid-19 coronavirus. It may have been more about people continuing to test positive for up to three months due to fragments of viral DNA possibly remaining after the Covid-19 coronavirus infection had passed.
This makes sense given the current state of the science. The answer to the big question of whether and how long you may develop immunity against the virus has been like taking a selfie while riding a roller coaster on a vibrating pillow: it’s still a moving target and unclear. As I have covered before for Forbes, scientists still don’t know for sure how immunity against Covid-19 coronavirus may work. Are you immune after you recover from an infection? If so, how long may immunity last? Does everyone develop this kind of immunity? Will everyone have the same degree and duration of immunity? What does this mean for vaccine development? How many people are really wearing pants while on Zoom? So many questions remain unanswered.
Several studies have suggested that immunity may last for at least a few months. In a research letter published in the New England Journal of Medicine in July, a team from the David Geffen School of Medicine at the University of California, Los Angeles (UCLA), led by Otto Yang, MD, a Professor of Medicine, described how they followed the antibody levels over time in a sample of 34 patients who had had mild Covid-19 coronavirus infections. Now 34 people isn’t a lot of people unless you want to play charades on Zoom or are waiting in line for the bathroom. Nevertheless, the study did show that recorded blood levels of immunoglobulin G in this sample dropped fairly rapidly after recovery from a mild severe acute respiratory syndrome coronavirus 2 (SARS-CoV2) infection. (You can say IgG instead of immunoglobulin G if you want to say it faster or are running from a tiger.) The average half-life for IgG in the blood was about 36 days, which meant that after about a month blood levels had dropped by roughly half. The research team followed each patient for an average of only 86 days so didn’t report if patients still had IgG after three months.
As I have written before, IgG is the important antibody for longer term immunity. To remember this, think “G” for “go” as in the song, “Please Don’t Go,” by KC and the Sunshine Band. Thus, the UCLA study suggested that the antibody immune response may still be around after three months but may soon thereafter be gone baby gone.
Another piece of evidence is a pre-print article entitled “SARS-CoV-2 infection induces robust, neutralizing antibody responses that are stable for at least three months” posted on medRxiv. The title of this pre-print kind of gives away the conclusion of the study, sort of like renaming the movie Avengers: Infinity War with the title “Large purple guy wears glove with bling and snaps fingers, making half of humanity disappear to set up a very lucrative sequel.”
For this second study, a team from Mount Sinai Hospital in New York City led by Carlos Cordon-Cardo, MD, PhD, a Professor of Pathology, Molecular and Cell Based Medicine, analyzed data from a database consisting of 19,860 people screened at Mount Sinai Health System in New York City for IgG against the SARS-CoV2. Over 90% of those who had experienced mild-to-moderate Covid-19 had measured IgG in their blood about three months after the infection. Moreover, these antibodies were able to neutralize the SARS-CoV-2 in test tubes. So, like the title of the pre-print said, you may have antibody protection against the virus for at least three months.
Keep in mind though that such a pre-print is not the same as a publication in a reputable scientific journal that has gone through peer-review. In other words, other real scientists haven’t had a chance to formally review the study, offer feedback, and suggest changes. The study is still in the “hey look, this may be interesting” phase and not the “here’s established scientific evidence” phase. So take the results from any study posted on medRxiv with a ham, cheese, and egg biscuit full of salt for now.
Another thing to consider is that IgG levels don’t exactly fit immunity to a T. The response provided by your immune system to the SARS-Cov2 in part can be a bit like a “friends with benefits” relationship. It can be quite complex with much more than what initially meets the eye. Your immune system can produce various types of lymphocytes to help with the immune response to an infection. These include B lymphocytes, which can secrete the aforementioned antibodies that are readily measurable by blood tests. However, other components, such as T cells or T lymphocytes, can be at work under the covers, so to speak. T cells have nothing to do with T-shirts but instead are cells that can help neutralize or kill viruses in different ways.
A study published in the journal Nature found T cells in people recovering from Covid-19 and that these T cells seemed to recognize the N-proteins in the SARS-Cov2. So even if antibodies were to disappear from your blood a few months after an infection, T cells could potentially hang around for longer and provide some defense against getting infected again.
Thus, the CDC’s current guidance is not surprising. The dearth of more definitive guidance may not feel very satisfying, but in the words of Wilson Phillips, hold on, the science is still emerging. Scientists need more time, resources, and funding to figure things out and gather more evidence. It’s been only about six or seven missed haircuts since this completely new virus emerged.
For now, the CDC is trying to give you some respite to actions that could get out of control. In theory, you could keep testing yourself up the wazoo after recovering from an infection. (Figuratively, of course, and not literally. You shouldn’t be testing your bottom for the SARS-CoV2.) After all, aren’t people in the White House getting tested each and every day for the Covid-19 coronavirus? The new CDC recommendation may give your nose a break. It may also keep you from quarantining constantly.
So, the CDC guidance may be more about practicing moderation than having strict definitive directions to follow to a T. The immune response, the situation, and in turn what you should do may still vary significantly from person-to-person and depend on how severe your infection happened to be. As Buffy sang to Big Bird on Sesame Street, different people, different ways. After all, maybe you don’t have to worry so much about getting re-infected in the three months after you’ve recovered from Covid-19. That is, unless you actually do get re-infected.