With all this talk about vaccines, Sofia Della Sala discusses immunity in people who have already had Covid-19.
There has been a lot of talk lately about our immunity towards Covid-19 and the antibodies associated with it. Before we get into the nitty-gritty of the topic, let’s quickly define what antibodies are and why we need them. Antibodies are proteins that selectively recognise molecules on the surface of pathogens (an organism that can cause us harm). The important action that antibodies take is that once bound to the pathogen (like SARS-CoV-2: the virus that causes Covid-19), they immobilise it, preventing it from being able to infect more cells. Not only that, but they also attract immune cells to come along and engulf the pathogen, thereby killing it completely. So in conclusion, antibodies are pretty nifty wee things.
Our body will naturally produce antibodies when we are infected with a new pathogen. This is the primary immune response. These antibodies will stay in our blood but eventually, their concentration will decrease over time. This decreased time varies from pathogen to pathogen. However, the cells that produce the antibodies (called memory cells) stick around, ready to fight the pathogen if it ever enters our body again. This is known as the secondary immune response; we are re-infected with the same pathogen and our body fights it off much faster and more efficiently due to already having the cells ready to go to battle.
With a disease like chickenpox, once you have it and develop the antibodies for it, you are basically immune for life because the immunity is so long-lasting. The reason you get colds every year is that immunity against the common cold is short-lived (in addition to the cold viruses’ ability to mutate, thereby sidestepping the line of defence you had built up last year).
The common cold and Covid-19 are both strains of the coronavirus. This is where things go out of focus. Not only does SARS-CoV-2 come from a family of viruses that don’t usually elicit long-lasting immunity, but it is also potentially prone to mutating (in fact, it already has). These facts coupled together don’t convince the pessimist in me about a secure path to immunity.
However, antibody responses aren’t one size fits all. Data from studies have shown that if you have been seriously ill with Covid-19, your antibody response is strong. Experts estimate this response could last on the time-scale of months or even longer. Alternatively, people who have had a mild infection display a weak antibody response and have lower antibody concentrations. The concern amongst the scientific community is that they might also wane faster, potentially leaving the person unprotected not long after having had the virus. Antibodies decrease at a very steady rate, so the more you start off with, the longer they will take to disappear completely. It is still not clear what all of this means in terms of getting the virus again.
But, does it matter if the antibody levels decline? Theoretically, we should have those sneaky memory cells that can induce the secondary immune response if we are ever re-infected. Right? Sadly, it is just too early to tell. However, don’t put the party poppers away quite yet. A study by Rockefeller University in the U.S., which has not yet been peer-reviewed (i.e, it hasn’t been verified by the scientific community), has found that in fact, we do produce memory cells and that the antibodies produced from these cells are even more potent than the ones produced the first time round.
So the mantra of the last few months still holds: nothing is certain. I am going to keep going about my (normal?) life, washing my hands, wearing a mask and avoiding people, but holding the hope of immunity in my memory, as my cells are too.