A note on COVID-19 immunity
The SARS-CoV-2 (COVID-19) pandemic has been going on forever now. Some of you may feel I am too late to the game, writing about it now, but I beg to differ. Now, when we are getting lax with our precautions even though the pandemic rages on, is the right time.
It is time to talk about something that is on everyone’s mind, immunity.
Before, I begin, I want you to be aware (or beware) of something. The thing is, our immune system is very complicated. Which is too bad because we really need to understand how the immune system reacts to the coronavirus.
Human immune system is the most complex part of our body outside our brain. Like a Rube Goldberg machine, it is composed of an absurdly intricate network of cells and molecules which summon, amplify, rile, calm, and transform one another. And yeah, it does all that while protecting us from various virus and other microbes.
Now, when we have gotten that out of the way, let us talk about immunity. Guess what!? We have been using this word all wrong, medically speaking.
When Immunologists use the term they simply mean that the immune system has responded to a pathogen (disease causing bad guys.) But most of us use the term to mean that we are protected or immune. Annoyingly, an immune response does not guarantee immunity. It all depends on how effective, numerous, and durable the antibodies and cells produced by the immune system’s response are.
Immunity, is usually a matter of degrees, not absolutes.
There is another aspect of immunity which leaves us scratching our heads. On the one hand we see some folks being asymptomatic and healthy, on the other, people falling gravely ill and families suffering the loss of a loved one. Also, does one become immune to COVID-19 after they have contracted it, like with small-pox and chicken-pox?
To answer these questions, we must first understand how the immune system reacts to coronavirus. Which is unfortunate because, you see, our immune system is very complicated.
I am no immunologist, but based on my albeit limited understanding all of it works roughly in the following manner.
The Generals
“Spartans! Hold the line! No prisoners! No mercy!”
The first line of defense involves detecting a threat, summoning help, and launching a counterattack. It begins as soon as a virus drifts into our airways, and infiltrates the cells that line them.
When cells sense molecules common to pathogens and uncommon to humans, they produce proteins called cytokines. Some cells raise an alarm, summoning and activating a battalion of white blood cells that go to town on the intruding viruses — swallowing and digesting them, bombarding them with destructive chemicals, and self-destructing while hugging the virus tightly. Other cells, delightfully called interferons, prevent the viruses from reproducing (interferon’s got no chill!)
These aggressive acts cause inflammation. Redness, heat, swelling, soreness — these are all signs of the immune system working as intended.
All the above events are a part of the quick, ancient, generic and broad innate immune system.
It’s quick, occurring within minutes of the virus’s entry.
It’s ancient, using components that are shared among most animals.
It’s generic, acting in much the same way in everyone.
And it’s broad, lashing out at anything that seems both nonhuman and dangerous.
What the innate immune system lacks in precision, it makes up for in speed. Its job is to shut down an infection as soon as possible. Failing that, it buys time for the second phase of the immune response: bringing in the specialists.
The Specialists
“Finally! The cavalry arrives! Just in time to save the day!”
Amid all the fighting in our airways, the messenger cells grab small signature fragments of the virus carry them to the lymph nodes. Lymph nodes house highly specialized and pre-programmed white blood cells called T-cells. Each T-cell is specialized differently, and comes ready-made to attack just a few of the zillion pathogens that could possibly exist.
For any new virus, we probably have a T-cell somewhere that could theoretically fight it. Our body just has to locate and mobilize that cell.
Imagine lymph nodes like a bar where mercenaries hang out waiting for a contract. The messenger cell bursts in with a grainy photo, showing it to each mercenary in turn, asking: Is this your guy? When a merc finds its mark, it gears up and clones itself into an entire battalion, which marches off to our airway.
Some T-cells are killers, which blow up the infected respiratory cells in which viruses are hiding. Others are helpers, which boost the rest of the immune system by activating B-cells which produce antibodies. Viruses attack by latching on to their hosts using proteins which fit the protein on the cell’s surface like a jigsaw. Antibodies are small molecules that can neutralize viruses by gumming up these structures and mopping up the viruses that are floating around outside our cells
T-cells do demolition; antibodies do cleanup.
Both T-cells and antibodies are part of the adaptive immune system. This response is precise but slower since, finding and mobilizing the right cells takes time. It is also long-lasting because it memorizes the threat and the master plan to neutralize it, keeping us safe in the times to come.
The Veterans
“Killing is easier than it should be. Staying alive is harder.”
After the dust has settled, most of the T-cell and B-cell forces stand down and die off. But a small fraction of these veterans remain bunkered in our organs and keep patrolling our bloodstream. In this final phase of the immune response, the immune system cools off and keeps a few specialists on tap. If the same virus attacks again, these “memory cells” can spring into action and launch the adaptive branch of the immune system without the usual days-long delay.
Memory is the basis of immunity as we colloquially know it — a lasting defense against whatever has previously ailed us.
This is a rather crude explanation of our body’s response to a pathogen.
But, what about some folks having the worst of a disease than others? What actually happens? Well … sigh … the thing is, our immune system is very complicated.
In general, the immune system’s response to COVID-19 is as expected. The innate immune system switches on first, the adaptive immune system follows suit and, the virus is vanquished. This is thankfully the case with most of the people who catch the infection.
But, there are other cases where there is deviation from this standard behavior.
Virus with tricks
Any good virus which can make people sick, has to have a few tricks up its sleeve (else the immune system with have it for breakfast.) The new coronavirus seems to rely on early stealth, somehow delaying the launch of the innate immune system, and inhibiting the production of interferons — those molecules that initially block viral replication. These delays cascade: If the innate branch is slow to mobilize, the adaptive branch will also lag.
Pre-existing conditions
Immune responses are inherently violent. Cells are destroyed. Harmful chemicals are unleashed. Ideally, that violence is targeted and restrained, but in some people the innate immune systems is already weakened through old age or chronic disease or the adaptive immune system underperforms. These critical vulnerabilities allow the virus to replicate unnoticed and go deeper to the more vulnerable parts of the body. The immune system can’t constrain it, but doesn’t stop trying. And this is also a problem as it causes a lot of collateral damage in its prolonged and flailing attempts to control the virus.
A matter of confusion
Normally, the immune system is programmed to implement different strategies of producing relevant cells to combat three broad categories of pathogens:
- Viruses and microbes
- Bacteria and fungi
- Parasitic worms
But, to err is human. And since immune system is an integral part of us, it gets confused just like we do. Though random and rare, the immune system in some cases is completely confused about what it is supposed to be producing and which instructions from which program to execute. This, as you can guess, has really terrible consequences for the body.
Though the above conditions are rare and most countries have observed a mortality rate of 2–3% on average, high and increasing cases lead to wider opportunities for varied immune response and hence higher prevalence of rare events.
Basically, the worse the pandemic gets, the weirder it will get.
One of the most pressing mysteries is what happens after we’re infected — and whether we could be again. Crucially, researchers still don’t know how much protection the leftover antibodies, T-cells, and memory cells might offer against COVID-19, or even how to measure that. Most they can do is make educated guesses based on our experiences with previous similar viruses.
It is crucial to continue taking precautions and stay safe unless a vaccine is out and we get vaccinated.
For now, let us take solace in the fact that despite the multitude of infectious threats that constantly surround us, most people spend most of the time not being sick. This is a testament to the efficiency and resilience of our immune system.
I am biased towards nature’s complexly beautiful mechanisms and patterns. Even though our immune system is vexingly complicated and at times unpredictable, I find it beautiful and fascinating.
I sincerely hope this post puts the pandemic and its consequences on our bodies in perspective. Nature has given us the best of tools to defend ourselves against these invisible threats. Let us stay put and do our part in bringing this pandemic to a swift end.
The end of this post is here. I leave you here hoping with all my heart that you will…wear a mask, wash your hands, stay indoors and stay safe.
References
www.cdc.org, www.who.int, www.theatlantic.com, www.nature.com, www.wikipedia.com, www.livescience.com, www.forbes.com, an amazing video from Kurzgesagt.
