Nature vs. Nurture: COVID-19 Immunity

I'm amazed at the ridiculousness of debates about basic concepts from immunology when SARS-CoV-2 is involved. The most recent question is about vaccination vs. natural immunity. Specifically, there are two questions extant:

  1. Is vaccination more (or less) 'powerful' at providing protection against COVID-19 than natural infection?
  2. If you get natural infection is it still necessary to get the vaccine?

Let's start with the first question, as it's the easiest to answer. First, I've already dismissed the ridiculous idea that SARS-CoV-2 adaptive immunity goes away after a few months. The idea that it would carries incredible implications that few laypeople understand, and it's also completely unfounded. The only reason people believe it is because they don't understand the intricate workings of the immune system, so they treat data that immunologists expect to see as evidence of something completely unexpected. This would happen with any pathogen, and if we don't get better science journalism before the next pandemic, the same misconceptions will be repeated as the immune system acts the same way with that virus as it has with this (and pretty much every other) virus.

As to efficacy of vaccination, it's kind of miraculous that vaccines are effective at all. The body has evolved to respond to actual threats in a very specified manner. If you're attacked by an airborne virus, you're likely to get attacked from the same place again next time. Your body will be mildly ready for another attack to come from the stomach or skin, but it will marshal most of its forces in the lungs. This will prevent you from even getting sick if you're exposed in the lungs again, but if your next exposure is elsewhere you'll still be able to fight off the infection better, even if you do get a little sick.

Knowing this, imagine injecting a respiratory virus into someone's arm. Except it's not the live version of the virus. It's dead, or mutated to not be harmful, or it's just the RNA from one or two proteins. What would you hope your body would do in this instance? Would you want it to launch an all-out attack on a bunch of dead virus? Before you answer, "Yes, let's attack anything we find that's suspicious!" remember the immune system is inherently destructive - to pathogens and to normal tissues. In fact, that's exactly how allergies work. They're an inappropriate attack by the immune system against otherwise-innocuous agents, to the point where the collateral damage you always get with an immune response becomes a problem.

However you would have responded to the above question, the body isn't keen on attacking things that aren't actively dangerous to your tissues. When we develop vaccines, we ride the line between "dangerous" and "innocuous" by adding some slightly toxic compounds to vaccines. They're easily degraded by the body, and stay local to the injection site, but the point is to cause some alarm bells to go off otherwise there's no point in injecting you with a dead virus.

Contrast this with natural immunity, where the immune cells in the lungs detect the virus and generate a robust lung-specific response. They also produce adaptive immune cells that circulate throughout the body, but they'll focus their defense on the lungs and be better prepared to prevent infection at the source.

My concern about the public misunderstanding of this phenomenon is that vaccination has one other drawback: it's not as long-lived as natural infection. By "not as long-lived" I'm not talking about months, but rather years. It has long been known that vaccine-provided immunity wanes faster over time than natural immunity, to the point where if it has been 10+ years since you got your childhood vaccinations you should consider going back in for a booster. Indeed, the most important time for this to happen is for women in their 20's before they begin childbearing. This is because the mother's immune system covers for the developing child's immune system from gestation through the first 6-12 months of life.

Unfortunately, nobody knows about this (except, perhaps for the friends of immunologists). Because nobody really cares about vaccination after childhood. It's assumed to be life-long. And now that this is a political issue a bunch of people are getting politically tied to the erroneous belief that vaccination is better than naturally acquired immunity. They believe that it's more long-lived and robust, which it's not.

To vaccinate or not?

This is a decision you should make with your doctor, but also make sure your doctor knows what they're talking about. If you're older (70+) you might want to get the vaccine even if you already had COVID-19. Even so, I don't think the vaccine will do much for you. That's because your naturally acquired immunity will be better in nearly every way than the vaccine-acquired immunity. If you're older and you haven't been vaccinated or gotten COVID-19 naturally, then you're likely rolling the dice.

If you're younger and you've had COVID-19 I don't see any reason to get the vaccine. It's just plain bad advice under most circumstances. (Unless you're caring for an elderly parent, and want to ensure maximal immunity.)

This advice isn't exactly something you can take to the bank, though. The problem is that a virus like COVID-19 is likely endemic at this point (as I've been trying to point out for awhile now). That means it will continue to mutate as it passes through the global population. Every few years the version of SARS-CoV-2 you're exposed to will be different enough that your previous immunity will be less effective at detecting it and preventing you from getting sick. Depending on your risk profile and who the next version of SARS-CoV-2 is most likely to kill, you may want to pick up a 'booster' that's specific to the most recent strain of the virus.


  1. Good post. I haven't seen exactly this information anywhere else, though I don't know that I've been looking. And thanks for bringing our immunological expertise to my blog.


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