An ongoing dialogue on HIV/AIDS, infectious diseases,
February 4th, 2022
Prior COVID-19 Is No Guarantee of Immunity
I’m no immunologist — a fact made vividly obvious to me several years ago when asked to teach a weekly medical student section that included cases and problem sets. The challenge was that the course combined immunology and microbiology.
I was on much firmer ground with the microbiology than the immunology, the latter often a wonderfully complex and mysterious system.
So why, then, am I about to wade into perilous waters and write about something very much immunology-related, a subject I’ve already confessed to being an amateur at? Because to us ID specialists, the immune system plays a critical role in how our bodies respond, clear, and protect us from various infections. We may not be true experts, but it’s highly relevant to what we do.
Additionally, I’m watching a debate unfold among ID colleagues, public health officials, epidemiologists, the lay public, politicians, and yes, even advanced degree-holding immunologists. It’s a debate about a critical issue facing the globe as we march on to the third year of the pandemic.
Namely, does infection with SARS-CoV-2 confer protective immunity?
Views range from “yes, certainly” to “maybe, sometimes” to “it depends” to “absolutely not.”
Everyone can cite their favorite study to back up their opinions — whether it’s an epidemiologic analysis of reinfection rates, or the cases of reinfection after prior COVID-19 that are less (or more!) severe than the first, or an in vitro study demonstrating robust (but then waning!) antibody responses, or how cells from people with prior infection continue to mobilize protective cytokines, or contrarily how prior infection inhibits these helpful cellular responses.
This doesn’t help resolve the issue, because of course they cite mostly the scientific studies and opinion pieces that support their views.
So for the price of subscribing to this blog, here’s my non-immunologist’s take, and warning — it’s a messy one with no precise answer:
Prior infection confers some degree of protective immunity. It varies from person to person, depends on the severity of the disease, with “just right” being more protective than mild or severe illness. (Cue classic Goldilocks analogy.) It’s not durable, is not guaranteed, and certainly isn’t going to lead to herd immunity on its own anytime soon.
Nope, no herd immunity by April 2022, just like it didn’t happen by April 2021.
Incomplete immunity conferred by prior episodes of COVID-19 is one critical reason that studies of populations continue to show that the unvaccinated have a markedly higher rate of hospitalization and death than the vaccinated — even though prior infection is becoming more common.
Two years into the pandemic, with major population surges, this remains an undeniable fact everywhere it’s studied — even though a higher and higher proportion of the unvaccinated have already had the disease. If prior infection were strongly protective, the gap between vaccinated and unvaccinated in risk of hospitalization would decrease over time. It hasn’t.
Omicron only exacerbated this reinfection issue, with many of us seeing or hearing about patients with repeat infections, sometimes quite quickly after a first infection:
Indeed, if we asked a group of primary care clinicians, emergency room folks, and other front-line providers to raise their hands if they had cared for or heard of people with more than one episode of COVID-19 — usually less severe, but sometimes more — 100% would have their hands up.
Incomplete protection from prior infection isn’t what any of us want to hear. But as we’ve learned again and again, wanting something from this virus doesn’t make it happen. The other night, someone in my family asked me whether now, as Omicron nabbed so many of us who previously escaped, can we at last move past this pandemic and get back to normal?
It’s such a good question!
I just wish I had a more reassuring answer.
In the meantime, let’s get everyone vaccinated, even those with prior infection. It’s a much more reliable way of getting protected, especially from severe disease.