A Vaccine Post That Doesn’t Talk About COVID?
Really?
Really.
I know my limitations and persuading anyone still unvaccinated against COVID-19 after almost 5 million deaths globally is going to take a better woman than me.
However negatively some people feel about vaccines though, there’s no doubt that since Jenner’s smallpox vaccine back in 1796, vaccines have saved millions if not billions of humans, livestock animals and pets from illness, disability, even death.
As brilliant as vaccines (and the dedicated scientists who spend their lives perfecting them) are, vaccines are only as successful as the immune system they’re nudging.
Which is why, to understand vaccines, we need first to review how our immune system defends us against germs (pathogens to scientists) like flu-causing viruses, sore throat-inducing bacteria, malaria-producing parasites and toenail-ruining fungi.
Our immune system has two separate but interacting branches, called innate and adaptive immunity.
Innate immunity encompasses everything from the physical barrier of our skin to germ-killing fevers and explosive germ ejection methods (diarrhea and vomiting!). These defense mechanisms operate a simple, “don’t know what it is, but it doesn’t belong here” philosophy and protect us even before we exit the uterus.
Our adaptive immune system has to specifically identify an invading pathogen before it can activate mechanisms to snuff out the intruder. When the pathogen is a first-time visitor, we can expect to be unwell until our adaptive immune system gains the upper hand, usually in just a few days. Once met though, pathogens are never forgotten and that same germ shouldn’t be able to make us sick a second time.
How does immune memory happen and how does it relate to vaccines?
Bear with me for a minute while we consider one of the best inventions of humanity, the library.
Imagine checking the book inventory for a country’s entire network of libraries and noting, weirdly, that there are one or two copies of every book written to date AND every book yet to be authored.
Only after a borrower asks for a particular title, does the Head librarian purchase multiple copies of that same book, reasoning if it’s been requested once, it’ll be requested again.
Our immune system operates along the same lines.
We’re born with billions of B lymphocytes (a type of white blood cell) whose raison d’etre is to seek out and identify pathogens. These lymphocytes are sprinkled throughout our body in own “lymphocyte libraries” like our lymph nodes and tonsils, but each of these B lymphocytes is ever so slightly different and can identify only one type of pathogen.
When an individual B lymphocyte recognizes and attaches to a particular pathogen, that’s its cue to start making thousands of (almost) copies of itself, some of which are called plasma cells and the rest, memory B cells.
The plasma cells start churning out thousands of identical antibody molecules every second, antibodies that recognize and target only the same type of germ that the plasma cell’s B lymphocyte parent first identified.
Antibodies quickly stick to pathogens, stopping them moving through the body spreading their infectious nastiness. They don’t do the actual dirty work of destroying germs but instead, give a chemical “germs over here” call out to phagocytes, who head on over, swallow and destroy the pathogen.
Just like Pac-Man, really!
For anyone not impressed or persuaded by the above, below is microscope-taken picture of a phagocyte (the red cell) “eating” some tuberculosis bacteria (the yellow rods). Sadly, the antibodies are way to small to see, even with a fancy microscope, but I promise they’re there!
(Is it just me or is this rather beautiful?)
We’re sick the first time we’re infected with a particular pathogen because it takes time for the pathogen and the literally only one or two B lymphocytes in the body, capable of recognizing that pathogen, to bump into each other. But once they do, those plasma cells and antibodies start rolling off the production line and our recovery starts.
It’s a little odd though.
Couldn’t we have evolved out of this “being ill” the first time we rendezvous with an unfamiliar pathogen?
Not easily.
Here’s the thing - even if we lived a thousand lifetimes, we wouldn’t encounter the majority of pathogens either on the planet today or potentially in the future.
And if we were born with multiple copies of every possible B lymphocyte design, we’d be an impossibly large collection of immune system cells and not much else!
Whereas an immune library of single copies has almost unlimited potential, with a B lymphocyte for every possible pathogen.
We’re sick when that new-to us cold virus comes our way but we don’t have to mask up for the rest of time that cold virus is circulating round the office - if our colleague coughs or sneezes it over us a couple of weeks later, we’ll be immune to it.
Thanks to our memory B lymphocytes.
Remember them?
Large numbers were produced alongside the plasma cells but their role is to wait patiently in case of a future visit by that same pathogen - even if that means hanging around for decades. Having numerous memory B cells distributed around the body means a much speedier identification of the pathogen and rapid production of high numbers of plasma cells and antibodies - the virus will be nuked without us ever knowing it was there!
Yes, most first-time visiting pathogens make us unwell but they don’t kill us and as the saying goes “what doesn’t kill us makes us stronger”.
Which, at least in terms of the immune system, seems to be true.
However, some pathogens are pretty dreadful, and that first exposure could be enough make us, or if we’re pregnant, our baby, really unwell or even finish us off.
And that’s where vaccines come in.
Vaccines all do the same, simple thing - they safely introduce a previously unseen pathogen to our immune system.
Those needle contents activate our adaptive immune system’s production of plasma cells and antibodies, but because the injected pathogen has been treated to make it harmless, we won’t get the whalloping headache of meningitis or the paralysis of a tetanus infection.
Live-attenuated vaccines, like smallpox vaccines for example, contain intact but weakened virus particles, capable of stimulating the production of memory cells and antibodies, but not the signs and symptoms of the disease.
Inactivated vaccines like those used to defend us against flu and polio go one step further and contain killed not merely enfeebled pathogen!
Sometimes, a vaccine only includes pieces of the pathogen, like the subunit vaccines for Hepatitis B and shingles. These shots contain parts of the pathogen big enough to poke our immune system into developing immunity but lack the key elements that would make us sick.
(The different vaccine types have advantages and disadvantages and here’s a great overview for anyone interested.)
Ultimately, vaccines are only effective if they can poke our immune system into making plasma cells, antibodies and memory cells. If we’re immunocompromised by chemotherapy or anti-rejection transplant medications, if we smoke or are just getting older, then despite having the greatest need for the protection that vaccines give, our immune system is least able to help them achieve that.
Which brings us to herd immunity, but sadly …a thought for another day.
As always, check out the geek notes for some great extra content,
Stay curious,
