How long does immunity to the coronavirus last?

If I think I had the virus before, am I still protected now?

Welcome to Not a Doctor, the only newsletter about health and science that accuses memory cells of going on too many benders.

I’m Melody Schreiber, a journalist and the editor of What We Didn’t Expect: Personal Stories About Premature Birth (which comes out one week from tomorrow!!!). I’m not a doctor, or a scientist, or really an expert of any kind. I just like to ask questions and try to find the answers to them.

I’m eager to dive into the topic on everyone’s mind: it’s my birthday month! Right? That’s what we’re all thinking about this week?

In all seriousness, I hope you have already voted or made a plan to vote safely.

Photo: Elvert Barnes

I will be watching election returns with great anxiety and hope. Now more than ever, science is inextricable from American politics, although it need not be so. Until that changes, the decisions we make this month will determine the course of millions of lives.

Which brings me back, of course, to Covid-19.

On Friday, the United States hit 100,000 confirmed cases in a single day. For context, it took nearly three months to reach the first 100,000 on March 27. And the trend now is only going up.

Let’s talk about what kind of immunity these millions of coronavirus-positive people will now have. I’ve written about this topic before, but now more time has passed, and there have been reports of waning antibodies and reinfections. So we’re diving in once more.

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Can I know if I’m immune, and how long that will last?

First of all, I want to talk to those of you who suspect you had Covid-19 at some point, but never got a test or a positive result. That really sucks! It’s incredibly frustrating not to know what is going on with your own health — especially if you hope that a previous illness might protect you from the virus now.

It’s possible to get a blood test (also known as a serological test) to see if you have antibodies. But there are a couple of flaws that make blood tests pretty unreliable at this point:

1. Many of the tests have high false negative and false positive rates — so it’s really difficult to trust the results.

2. If you do have antibodies, they’re usually only present for a few weeks or months after the illness (more on this later). So, you may have had the illness, and you may take a very accurate test — and it still might come up negative.

(If you’d like to learn more, I wrote about serological tests both for this newsletter and for The New Republic a few months ago.)

As much as it sucks, if you haven’t had a confirmed case, you should act like you have never had Covid-19, and continue taking all of the necessary precautions. If it’s any consolation, that’s the same advice usually given to people who have had confirmed cases, as well, as scientists are still trying to figure out how protective antibodies and immune responses can be.

However, researchers are working at breakneck speeds to understand a virus that’s younger than the microwaveable mac and cheese I just found in the back of my pantry.

Two new studies that came out recently indicate that most people do develop some form of immunity that lasts for a couple of months. The sicker you get, the longer your immunity may last.

It’s important to note, however, that not all antibodies are created equal. You might have a high level (called “titer”) of antibodies that are just so-so at neutralizing the virus. Or you could have just a few antibodies that are SUPER effective. It’s hard to know which are which without extensive lab tests.

(For more on how antibodies work, check out this nerdy piece I wrote recently, wherein I did the YMCA… for science!)

One of the recent studies confirmed that your antibodies start disappearing after a month or two — but that’s not surprising at all. Imagine if you kept actively producing antibodies for every illness you ever fought off! Your blood would be cement, and you would waste a ton of energy manufacturing antibodies you don’t even need most of the time.

Instead of continuing to produce these antibodies indefinitely, your body does a really cool thing: it trains T-cells, or “memory cells,” to recognize the virus, and B-cells that kick into high gear to produce antibodies quickly.

That means, even after you can’t detect antibodies in a blood test anymore, you could still have some immunity to the virus — at least, until your memory cells have a few too many margaritas and start forgetting.

This immunity probably lasts for at least five months, researchers found, although you could have some level of protection for longer. Whether you develop immunity at all, and how long it lasts, depends on several factors (severity of disease, your own immune system and the effectiveness of the antibodies you produce, etc).

It’s not clear if immunity can last longer than a few months, because the virus hasn’t been around long enough to find out. However, most coronavirus immunity only lasts a few months to a year.

That means you may have fought off Covid-19 last winter or spring, but the virus is ready for round 2 now. And you might not be aware that suddenly you’re boxing with no gloves or headgear anymore. (Apologies to readers who actually know stuff about boxing.)

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Will partial immunity make me get less sick the second time?

One unanswered question we have is how sick you get the second time around. With some diseases, like dengue, you actually get sicker each time you get it. With other viruses, including some coronaviruses, you often have milder subsequent cases, as I mentioned in a previous update.

It’s worth mentioning, however, that at least one patient with a confirmed case of reinfection experienced mild or no symptoms the first time around, but got sicker the second time. So if you had a mild case before — and “mild” here means you weren’t hospitalized — you could have a more severe illness now.

Although there are only a handful of confirmed cases of reinfection so far, that could be because of gaps in testing and contact tracing for the virus (particularly in the early months) in the United States.

“[W]e are probably severely underestimating the number of asymptomatic reinfections,” one well-known virologist wrote in The Lancet.

This is, honestly, what worries me most about this coming winter. (Okay, other things also worry me a lot.) It’s very possible that everyone who got sick seven or eight or nine months ago is now vulnerable, to some extent, once again.

And even if you’re lucky (ugh, what luck) and get a milder case the second time — especially if you have no discernible symptoms — you are statistically more likely to spread the virus, because you might not even know you’re sick.

That means we need to continue taking as many precautions as possible, both for ourselves and for others in our chain of connections. It sucks — pretty much everything about this pandemic sucks! — but these are the actions we can control.

The other action, of course, is voting. (Full circle!) And holding our officials accountable, so that they will stop the virus in its tracks, reopen schools and businesses safely, and protect as many people as possible.

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As always, please leave a comment or reply to this email if there’s something I’ve overlooked or something you’d like clarification on. You can also follow me on Twitter and Instagram, if you’re so inclined.

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