Check for recent asymptomatic Covid before getting new booster?
September 11, 2022 6:40 PM   Subscribe

As far as I know, I haven’t had Covid yet. No positive tests and no symptoms. This seems really unlikely, though, since at minimum 70% of the US population has been infected, according to CDC data from July. So if I’ve actually had a recent asymptomatic case, how should that inform my timing for getting the updated booster — wouldn’t it be best to wait 2-3 months as is recommended for anyone who’s had a symptomatic case? Should asymptomatic people try to determine whether they have, in fact, had a recent infection before getting a booster?

I’m not near my doctor for the next several weeks, so I’d have to take an OTC test or go to a local pharmacy. How reliable are they at distinguishing between antibodies from infection vs. from the vaccine? My last booster was 9 months ago.
posted by theory to Health & Fitness (5 answers total)
You’re fine. You do not need to worry about an asymptomatic case. If you had an asymptomatic case it means your immune system wasn’t working that hard. It will be fine.
posted by Geckwoistmeinauto at 6:47 PM on September 11, 2022 [4 favorites]

Best answer: If you want you could get a PCR test or a rapid test and see if they show something. I wouldn't do anything beyond that. The guidance for boosters doesn't tell people to go out of their way to figure out whether they might have gotten Covid without knowing. Just follow the guidance. If you know you've had Covid, wait a couple of months. Otherwise get the booster.
posted by Winnie the Proust at 6:48 PM on September 11, 2022 [3 favorites]

Best answer: I think your reasoning that you've likely had it is flawed. Stuff that has a 30% chance of being true is true all the time. Trump famously had a 30% chance of becoming president.

About 50% of people say they have had covid. If the 70% estimate is correct then 40% of those who don't know they've had covid have had it. So just based on no knowledge at all about you, you probably haven't had covid. Now if you're been on the more careful side, and you're on the more privileged side then figure your chance is even lower. I'm going to assume on the basis if your metafitler membership, which probably correlated with both privilige and carefulness, that you've been more careful and priviliged. So let's say a 20-30% chance you've ever had it.

Now that's EVER. Have you had it recently? Well it's been two and a half years. Let's say 12 3-month periods. If we place the probability evenly that's a 1.6%-2.5% chance you had it in any particularly 3 month period. The risk probably isn't evenly spaced through those 2 month periods though. If you feel like the most recent 3 months have been your highest risk, then let's go crazy and say there's a 5% chance you had covid in the past 3 months.

I wouldn't worry about it.
posted by If only I had a penguin... at 6:55 PM on September 11, 2022 [6 favorites]

Best answer: > I’m not near my doctor for the next several weeks, so I’d have to take an OTC test or go to a local pharmacy. How reliable are they at distinguishing between antibodies from infection vs. from the vaccine?

The tests you're going to get at the local pharmacy will do nothing to detect antibodies (the proteins that your body makes that fight infections.) They will be either a PCR test (detects viral nucleic acids) or a rapid antigen tests (detects little chunks of viral protein), both of which detect virus that your body is fighting right now. For technical reasons, the PCR tests are more sensitive (i.e. more likely to detect a very early infection or the last dregs of an infection) but they're still testing for the infection itself, not your body's ability to respond to an infection. (Testing for antibodies exists, but it is much, much less available outside of clinical settings or vaccine trials.)

And - utterly anecdotally - it's certainly still possible not to have been infected. I've been PCR-tested at least once a week for two years; I've never had a positive one. By your reasoning, if you aren't testing regularly, you could always have a current or recent asymptomatic case and thus should always wait another 2-3 months, which clearly doesn't actually make sense because you'll never get boosted as a result.
posted by ASF Tod und Schwerkraft at 7:07 PM on September 11, 2022 [12 favorites]

Best answer: You can, in theory, get an antibody test that could tell you that you have already had Covid at some point (these tests look for nucleocapsid antibodies, not the spike antibodies you get from vaccines, so there is no worry about distinguishing vaccination from past infection). But an antibody test won't tell you when you have Covid, so it won't help. Even if you have had Covid, it could easily have been in January or April or some other time, in which case now would be a great time to get vaccinated again.

Realistically, the chance that you've had Covid in the last 2-3 months is relatively low. About 40% of infections are asymptomatic according to the UK ONS infection survey, but not that many people have been infected in the past 2-3 months, so your chances are probably around 1/10 of having had asymptomatic Covid in the period. But all that will happen if you had Covid and get the vaccine earlier than is ideal is that you will be a little bit less protected than you would be otherwise (but you'll still be more protected than you would be if you hadn't been infected at all). In any case, there's nothing you can do about this because there is no test that will tell you when you had Covid. Go forth and get vaccinated without worry!
posted by ssg at 9:04 PM on September 11, 2022 [2 favorites]

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