Reinfection, Reactivation, and Relapses — What we Know and Don’t Know About COVID Immunity

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Photo by Markus Spiske on Unsplash

The World Health Organization has cautioned us that there’s “no evidence” of immunity after catching COVID, whilst scientists have found “good neutralizing antibodies” in the blood of survivors. Many people were alarmed by the report of sailors from an aircraft carrier apparently catching COVID-19 twice in quick succession. The fear is obvious. If nobody gets immunity then there can’t be a vaccine and we can never beat this thing.

So, let’s unpack this some and talk a bit about immunity, reinfection, and relapses.

How Do We Get Immunity?

Our bodies have two levels of immune system. The first level is the innate immune system. This identifies intruders and fights a holding action while the second level, the adaptive immune system, prepares its weapons.

In some cases the innate immune system may defeat a virus before the adaptive immune system really gets into gear. This can result in not developing immunity, and sometimes happens with colds. If you get a very mild cold, give it to a coworker, then get it back from them, likely your adaptive immune system never woke up.

When your adaptive immune system wakes up, cells called B lymphocytes start to experiment with antibodies. Antibodies are cells programmed to fight a specific invader. It can take your immune system a while to create these, and while it does, your innate immune system is throwing everything at the virus and making you sick. A fever is your immune system raising your body temperature because viruses don’t like that. (One of the big issues with COVID is it can trigger a cytokine storm, which is when your immune system goes so far into overload to try to kill the virus it risks killing you as well).

Once your body has created antibodies to fight an intruder, those antibodies stick around. Over time, however, if your body doesn’t encounter the same intruder again, you stop making those antibodies, although you may keep the program to do so. You can only make so many, after all.

If the virus mutates, sometimes the antibodies will stop working. Or they will only be partially effective. Immunity is a dimmer switch; you might be immune in that you don’t catch it, or you might simply not get as sick.

In most cases, thus, your immunity to a disease is time limited and potentially partial.

There are a few viruses that do confer permanent immunity. They include measles and mumps. Things we call “childhood diseases” because generally, pre vaccination, you caught them once when you were young and then didn’t have to worry about them again. But up against the large number of viruses that don’t we can immediately come to the reasoned conclusion that any immunity to SARS-CoV-2 will be relatively short term.

But People Are Catching it Again Right Away

The concern about people recovering from COVID, leaving the hospital and then immediately becoming sick again started in South Korea. A number of people were testing negative, and then testing positive again later. Needless to say, the Koreans investigated this. The conclusion they came to was that this is not reinfection. They were unable to culture live virus from the patients (which means they are not contagious).

What is happening is that the PCR tests used to detect COVID are both very sensitive and somewhat tricky to administer. They are sensitive enough to detect dead virus, which can stay in one’s system for a while (especially with large viruses like SARS-CoV-2) but hard enough to administer for false negatives to occur.

Additionally, in some severe cases we’ve found that there is no virus in the nasal cavity, but it IS in the windpipe or lungs. It’s possible that in some cases the virus is being knocked out of the nasal cavity and then growing back in there.

In the case of the 13 sailors, this was a little more worrying. Five of them developed “flu-like” symptoms. Some health care professionals are concerned about reactivation (which I’ll talk about). There are also a few cases that were definitely a relapse, which seems to be what happened to the sailors. The negative tests would be a mystery if the tests were more accurate (there are healthcare workers reporting that people who obviously have COVID-19 are sometimes testing negative).

What’s worth noting, though, is that these cases are rare. Even if they are reinfection, if COVID-19 didn’t grant some immunity in most cases, we would be seeing a lot more of this.

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Photo by JC Gellidon on Unsplash

What About Reactivation?

Most of us have had chicken pox. The chicken pox vaccine was not licensed for use in the U.S. until 1995.

Chicken pox is an annoying childhood illness that makes you break out and itch. I was one of the unlucky ones who got it as a teenager, which means I was old enough to be really annoyed about being quarantined.

Shingles is a really nasty disease generally experienced by older adults (although you can get it at any age) that results in a painful rash…and can leave you in pain for months or years.

Because pretty much every kid gets chicken pox, it took us a while to work out a key fact: You only get shingles if you have had chicken pox.


They’re caused by the same virus. Varicella zoster, the virus that causes both, can hang out dormant in your body for years or decades and then mysteriously reactivate. Essentially the virus is benign…until it isn’t. The reason shingles generally affects older adults is simple: Immune systems weaken with age. (This is also why older people are getting sicker with COVID-19).

Stress can also cause a virus to reactivate. Generally, viruses that reactivate fall into the herpes group. This includes Epstein-Barr virus, the virus that causes mono. (This is why if you have had mono once you can randomly get it again later).

So, can COVID-19 become dormant in our system and reactivate later?

We have absolutely no idea. Persistent infection (long-term asymptomatic carriers) has been found in canine and feline coronaviruses, but I was unable to find a mention of this with other human coronaviruses.

If it is, this is obviously not great news, especially as dormant viruses can be hard to deal with. However, again, the rate of positive after negative testing is low and can easily be explained by issues with the tests.

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Photo by CDC on Unsplash

If There’s No Immunity, There’s No Vaccine

Believe it or not, this is a fallacy. Let’s take tetanus. Tetanus is a bacterial disease that’s sometimes called lockjaw. It’s highly unpleasant and can be fatal.

There’s a vaccine against tetanus that, in humans, lasts ten years…despite the fact that natural infection with tetanus confers no immunity whatsoever.

Vaccines are designed to very specifically train our immune systems to deal with an infection. Immunity from a vaccine is generally better and longer lasting than natural immunity, and that’s even with vaccines that aren’t that great, like influenza.

So even in the unlikely situation that nobody gets immunity to COVID that lasts even a few days we might still be able to manage a vaccine.

More likely, based on what we know of SARS, a very closely related virus, the majority of COVID patients will gain at least partial short-term immunity, and “short-term” in this case means a year or two.

That doesn’t mean you should go “Oh, I had COVID already, I’m fine.” We still don’t have good antibody tests, COVID is easily mistaken for other diseases if it doesn’t put you in the hospital, and we don’t know for sure how long immunity will last.

But it does mean that you shouldn’t panic about the nightmare of everyone just getting sick over and over again. So far, that isn’t happening and it fortunately seems unlikely.

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Freelance writer, freelance editor, novelist and short story writer. Jack of many trades.

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