Why haven't I caught COVID?

June 10, 2022 1:13 PM

For most of pandemic I've been working with the public, face-to-face, including a year at a COVID testing site, in and around Seattle. I wear proper masks and eye protection now, but there was a long spell where I was wearing just a cloth mask or a single surgical mask, and the people I encountered at various jobs often weren't in masks. Has my constant but low exposure to COVID helped me fight it off? Or did I just get lucky?

I'm healthy, quadruple vaxxed, and nobody in my household has tested positive for COVID (we think one of us had it in Feb 2020).

I'm jinxing myself by posting this, aren't I?

posted by The corpse in the library to Health & Fitness (36 answers total)

nobody knows the answer to this question. we can chat about it, but if anybody knew the answer, covid would have been controlled by now.
posted by fingersandtoes at 1:17 PM on June 10, 2022 [16 favorites]

Have you had antibody tests done to check for prior infections? You may have had it but been asymptomatic. When people ask if I've had COVID I wind up saying "Not as far as I know," because that's as much certainty as I can have. :/
posted by curious nu at 1:19 PM on June 10, 2022 [19 favorites]

Response by poster: > nobody knows the answer to this question.

Fair, as far as my individual situation goes, but maybe someone has read a study about healthcare workers, or teachers, or other people who have steady low-dose exposure.
posted by The corpse in the library at 1:22 PM on June 10, 2022 [2 favorites]

Response by poster: > Have you had antibody tests done to check for prior infections?

No, and that isn't an option now that I've been vaccinated, right? Both Pfizer and Moderna.

(I shall now be quiet like a good Asker.)
posted by The corpse in the library at 1:23 PM on June 10, 2022 [1 favorite]

Yeah, I was part of a nationwide NIH study which required me to send some blood a couple of times. They found that some huge percentage of people who had not had covid had in fact had it and been asymptomatic. The study was such that they couldn't tell me if I'd had it, so I don't know for sure, but like you I've been around quite a few unmasked people and haven't ever tested positive.
posted by mareli at 1:26 PM on June 10, 2022 [5 favorites]

I have read several speculative but still scientific commentaries (New Scientist, that sort of thing, written by people with some background) speculating that just as studies are beginning to suggest that there are some invisible genetic variances that make people more vulnerable to covid, there may be some invisible genetic variances which make them less vulnerable. I personally would not bet the farm on this, but it's possible that you just....aren't that susceptible to covid.
posted by Frowner at 1:27 PM on June 10, 2022 [8 favorites]

I don’t know. And I’m not just saying that. I managed to go two years without testing positive, even though everyone else in my household tested positive at least once. My wife tested positive twice. We spend a third of our lives a foot away from each other. But I never got it. I’d been mildly sick several times, including around the times my wife tested positive, but my tests kept coming back negative. Until last week. I started feeling bad on Wednesday. The day before, Tuesday, I spent the entire day with my mom and my sister who were visiting from out of town. Once I tested positive, I called them, and they were both negative. My wife and kids were negative. It’s like a game of duck duck goose. Sometimes it skips you, sometimes it doesn’t.

I have read some mainstream media articles about this. There was one last week in the New York Times. The gist always seems to be “we don’t know”. I have seen articles that say there do seem to be some people who are more resistant, but I haven’t seen anything linking that to a specific factor.
posted by kevinbelt at 1:27 PM on June 10, 2022 [6 favorites]

Well, your question is a bit more abstract than that - you very well might have had a case that you were unaware of.

Per the CDC, apparently 60% of the US population show antibodies of having covid.

That leaves 40% of the population not having it at all.

Per the stats, 25% to 80% of the people who had covid weren't aware. (really wide range, but best I could find).

So that means somewhere between 15% to 51% of the US population had it and were aware they had it.
posted by The_Vegetables at 1:31 PM on June 10, 2022 [3 favorites]

nthing you may have actually had it but been fully asymptomatic.

A friend of mine had a completely asymptomatic COVID case. The only reason she found out is because she had to take a PCR test for travel and got a positive result. She never developed any symptoms.
posted by mekily at 1:32 PM on June 10, 2022 [1 favorite]

Here's an up-to-date study from Los Angeles.

Here's the abstract of a review article, i.e. one that summarizes a number of research articles.
posted by mareli at 1:34 PM on June 10, 2022

The CDC has estimated 60% of the population has had COVID. Your level of protection efforts - by wearing any mask at all, none the less "proper masks and eye protection" - is significantly above the average person in the USA, so it's not unreasonable to think you are in that 40%. Further, masks (especially respirators) are quantifiably beneficial in reducing chance of infection - and you have that on top of vaccination. That vaccination+booser, in your region, reduces probability of infection compared to people who are not fully vaccinated.

In short, masks work. Vaccines work. Boosters work. You have all three. And even the people that don't have all three (ie, the average American), have a 40% chance of never being infected.
posted by saeculorum at 1:36 PM on June 10, 2022 [10 favorites]

As one of these people: heck if I know, nobody knows, we may never know and yeah, you probably did jinx yourself by posting this :P I have a few articles on this bookmarked, but all paywall.

WaPo: The lucky few to never get coronavirus could teach us more about it:

"Scientists don’t know why some people might be impervious to the coronavirus, but Nuzzo said one hypothesis could be that some individuals have fewer receptors in their noses, throats and lungs for the virus to bind to. Other possible explanations could be prior exposure to a related virus or simply being born with an immune system better suited to fighting SARS-CoV-2.
But finding individuals who have truly never had a coronavirus infection — not just those who had an asymptomatic infection or less severe case of covid-19 and did not know they had contracted the virus — is tricky.
“Those people should be exceedingly rare in the United States at this point,” said Christopher Murray, director of the Institute for Health Metrics and Evaluation at the University of Washington and who helps develop models that estimate how far the virus has spread.
IHME models suggest that the number of people who have had the coronavirus in the United States may be even higher than recent CDC estimates based on blood tests, Murray said. The CDC said nearly 6 in 10 Americans have had the virus at least once; IHME estimates that total is closer to 76 percent of U.S. residents.
Antibody tests can rule out people who have an immune response to the virus, but some of those tests cannot distinguish between people who have antibodies because of vaccines and those who have had the coronavirus, Murray said. The accuracy of many antibody tests wanes over time, so they may not identify someone who had been infected months ago, he added.
“It’s an elusive target,” Murray said.
Once researchers find people who avoided coronavirus infection, the next challenge is determining how they did so.
Because masks, vaccines and social distancing can significantly reduce transmission, those factors may eclipse any biological differences between people who have not been infected and those who have tested positive.
“It’s got to be a combination of caution, circumstance and luck,” said Bob Wachter, professor and chair of the department of medicine at the University of California at San Francisco, who has not had the coronavirus.
People who always wear masks in indoor public spaces, stay up to date on vaccines and boosters, test frequently, and avoid high-risk gatherings or travel may have had fewer chances to catch the virus, Wachter said. Low levels of community spread in certain regions or the ability to work from home may also have protected some individuals better than others, he said.

NYT: My Family Got Covid. So Why Did We Test Negative? One kid got sick and tested positive, two others were sick but kept testing negative, the author never got sick and kept testing negative.

My husband and I are vaccinated and boosted, and our kids are vaccinated but not yet boosted. This is a relevant question because, if you’re exposed to the virus that causes Covid-19, “your immune system kicks into action a lot faster if you’re vaccinated versus not vaccinated,” said Gigi Gronvall, an immunologist at the Johns Hopkins Center for Health Security in Baltimore. And this rapid response changes everything about what happens next.
First, the swift immune reaction slows the rate of viral reproduction and spread. “This is what the vaccines are there for — to educate your immune system so that it gets a jump on the invaders before they are able to replicate out of control,” Dr. Gronvall said. Because the virus doesn’t replicate as quickly in vaccinated people, they may be less likely to test positive for Covid-19 after coronavirus exposure, because their immune system “keeps the viral load below the level of detection,” said Juliet Morrison, a microbiologist at the University of California, Riverside.
It’s possible, then, that my husband and son did catch Covid-19, but their vaccinated immune systems fended off the infection so well that they never had enough viral proteins in their nose or throat to test positive. And their continual negative tests probably meant that they were never that contagious, Dr. Morrison said.
If my husband and son never tested positive, why did they feel sick? Even if a vaccinated person doesn’t have much virus in their body, they can still have powerful Covid symptoms, the experts told me. That’s because many illness symptoms — fever, malaise, runny nose, fatigue — are actually caused by the immune system’s response to the virus, rather than the virus itself, Dr. Gronvall said.
And as for why I felt fine, Dr. Morrison said that perhaps my immune system fought off the incoming virus so quickly that I didn’t even have a chance to feel sick. “It sounds to me like you were definitely exposed,” Dr. Morrison told me. But, she explained, maybe I had high levels of vaccine antibodies or immune cells called T cells that were able to kill the invading virus before it had a chance to alert the parts of my immune system that would incite symptoms.

posted by jenfullmoon at 1:40 PM on June 10, 2022 [6 favorites]

Response by poster: Oh, important note: I've been PCR tested weekly, if not more often, for the past year.
posted by The corpse in the library at 1:41 PM on June 10, 2022 [6 favorites]

No, and that isn't an option now that I've been vaccinated, right? Both Pfizer and Moderna.

Nucleocapsid antibody tests don't test for spike protein antibodies, which is what the mRNA vaccines make your body produce.
posted by zsazsa at 1:43 PM on June 10, 2022 [14 favorites]

As we allowed the virus unlimited opportunity to reproduce and mutate, it got more transmissible. That's why the masks that worked earlier became insufficient. If everyone had just worn cloth or surgical masks when this started, we could have put this guy out of business, but we chose to let it prosper instead. The result is that now we need better masks.
posted by bleep at 1:44 PM on June 10, 2022 [3 favorites]

No, and that isn't an option now that I've been vaccinated, right? Both Pfizer and Moderna.

I've looked into this because I've had the same curiosity (over two years, to my knowledge have never been infected, and I have more or less been participating in "normal life" since receiving dose 2 last year, although not to the same extent as pre-2020), and it's an option if you get a nucleocapsid protein antibody test. A spike-based antibody test will not tell you if you've ever been infected, because the vaccine means you have spike antibodies, but if you get one for the N protein, that's based on a different protein that's not included in any vaccine authorized for use in the US. So if you were to test positive, it means you were exposed and developed antibodies at some point.

You may have to pay out of pocket for it and possibly get a physician to order one for you. Not sure if insurance would cover it, but my guess would be no.

I'm very curious to have an idea of whether I was an asymptomatic positive at some point but probably not curious enough to fork over a few hundred dollars or whatever it would be to pay out of pocket for an antigen test.
posted by Kosh at 1:45 PM on June 10, 2022 [3 favorites]

You may have a good immune system, or are lucky. Even simple masks help some. Buy a lottery ticket!
posted by theora55 at 1:47 PM on June 10, 2022

I had read somewhere that there's a small, very small chance there's a genetic reason as to why some people have not gotten COVID. The same article also speculated that prior infection of another Coronavirus may also have helped. But it's all speculation at this point. I have 4 family members, some double and boostered, some single, and some no vax at all, who have been mostly unmasked and out in public the whole pandemic, and have never gotten it. And for 3 of them, if one had gotten, the likelihood of the other 2 getting it would have been quite high due to living so close together.
posted by 922257033c4a0f3cecdbd819a46d626999d1af4a at 1:55 PM on June 10, 2022 [1 favorite]

Has my constant but low exposure to COVID helped me fight it off? Or did I just get lucky?

I think your constant exposure probably helped you fight it off.

Gertrude Rey wrote an interesting essay about the varieties of vaccine induced and exposure induced and maintained immunity in this pandemic over at virology blog:

Do SARS-CoV-2 vaccines induce sterilizing immunity? The answer to this question is complicated. There are many studies showing that most people have high levels of antibodies in the months following vaccination, and this large proportion of circulating antibodies could likely sequester an incoming virus before it has a chance to enter cells, infect them, and replicate. In this sense, the SARS-CoV-2 vaccines do induce sterilizing immunity, but only within a certain time period after vaccination. As antibody levels contract over time (a normal process), they leave behind a baseline population of memory B cells that can quickly expand and mass-produce new antibodies upon a subsequent encounter with SARS-CoV-2. Likewise, memory T cells can quickly react to incoming virus and virus-triggered signals, and destroy infected cells. Therefore, it is likely that when circulating SARS-CoV-2-specific antibody levels decline months and years after vaccination, the collective activity of memory immune cells will protect one from disease, but probably not infection, meaning that the SARS-CoV-2 vaccines no longer induce sterilizing immunity at that time. In other words, vaccinated people could briefly replicate and transmit low levels of virus, at least until memory immune responses kick in, which then prevent illness and additional viral replication and spread.

The fact that you were continuously exposed to whatever came through the door over a long period not only kept the level of your immune response from tailing off, but made it more likely that you were exposed to each incremental step in changes in the virus over time, allowing your immune system to continuously update its ability to recognize the virus.

Whereas if you had remained isolated during a similar interval, the virus would have been more likely to accumulate a level of changes which might have dampened your immune responses enough to allow a clinical infection to develop.
posted by jamjam at 2:03 PM on June 10, 2022 [4 favorites]

I'm not superstitious, but, whew, you are brave.

It would be interesting to find out someday, but I don't think we have any idea right now. I've been in NYC virtually the entire time since March 2020. I'm lucky enough to be able to work from home and not to be a caregiver for small humans, and, while I have avoided the permanent catastrophe mindset some people have adopted, I've been fairly careful about being in public, but, when you look at the statistics, it's hard to explain. I assume my number will be up sooner or later.
posted by praemunire at 2:16 PM on June 10, 2022 [1 favorite]

I was one of these people. Lived in DC since March 2020, work from home and took precautions, but not extreme precautions and never got it... until this week when my partner and I both got sick. Hope your luck continues to hold out.
posted by fancypants at 2:21 PM on June 10, 2022

Good luck.
Good management.
Good genes.
You already had it but didn't notice.

Any combination of the foregoing.
posted by i_am_joe's_spleen at 2:24 PM on June 10, 2022

My old lab [I R retire] in Dublin is part of an international consortium, the Viral Resistance Project, looking for people who shared spittle a bed with someone who tested positive but they themselves remain negative. Newspaper report.

The backstory is that they/we were working with a cohort of women who received therapeutic blood products subsequently found to be contaminated with Hep C virus who stoutly refused to be infected [PCR -ve, antibody -ve]. Their innate immune system was meticulously scanned to see if "all" these women had some genetic variant in common which wasn't shared by similar women who did catch hepatitis. backback story: anti-D scandal.

Current hypothesis is that some folks have a genetic variant which prevents SARS-CoV2 from getting a toe-hold.
posted by BobTheScientist at 2:36 PM on June 10, 2022 [6 favorites]

The fact that you were continuously exposed to whatever came through the door over a long period not only kept the level of your immune response from tailing off, but made it more likely that you were exposed to each incremental step in changes in the virus over time, allowing your immune system to continuously update its ability to recognize the virus.

What you are suggesting is repeated asymptomatic infection. While there is certainly a significant amount of asymptomatic infection happening, there's pretty good evidence (e.g. from the UK ONS infection survey that tests people weekly or surveys of N-antibody levels from blood donations) that people are not being infected repeatedly to that degree.

Whereas if you had remained isolated during a similar interval, the virus would have been more likely to accumulate a level of changes which might have dampened your immune responses enough to allow a clinical infection to develop.

This is not how Covid has evolved. We have not observed slow drift across the population, but different variants replacing each other in the general population in waves. The intermediate evolutionary steps have happened in one person or possibly a small group of people or other animals. Except for BA.4 and BA.5, which are just starting to cause a significant proportion of infections in the USA, and subvariants like BA.2.12.1, none of the major variants like Delta or Omicron were descendants of another major variant. In other words, the changes in immune evasion we have seen between variants have been large, discrete changes, not slow, continuous changes.
posted by ssg at 2:52 PM on June 10, 2022 [9 favorites]

I live in a state where very little was done to control the spread of COVID and which consequently had, at one point during the fall of 2020, the worst rate of new cases per capita in the entire world. Because I had a severe and life-threatening reaction (anaphylaxis) to a component of another vaccine many years ago, every physician I spoke to was hesitant to administer any of the available COVID vaccinations, so I went unvaccinated until September of 2021 and am now only double vaccinated. I worked at a hospital during the tail end of the worst of the pandemic, although in the pathology lab rather than in a department with direct patient contact. I've been around multiple unmasked people who subsequently tested positive.

As far as I'm aware, I still have not yet had COVID. At this point, I just assume I had it and was totally asymptomatic, which is surprising as I have fairly severe asthma. I just hope that I didn't transmit the virus to anyone else who might not have been so lucky.
posted by easy, lucky, free at 3:15 PM on June 10, 2022 [2 favorites]

I wear proper masks and eye protection now, but there was a long spell where I was wearing just a cloth mask or a single surgical mask, and the people I encountered at various jobs often weren't in masks.

Eh this would have described me too (well, except for the eye protection) until two months ago, when whoopsie doodle, got COVID. I wasn't doing anything different when I got it, and ironically was probably being more careful than usual at the time because I had an event coming up.

Best I can figure, the only thing that might have nudged the odds against me is that some of our mask mandates officially came down shortly beforehand. Most people at my store and gym kept masking anyway, and the mandate on transit remained, but there were certainly a handful of unmasked folks I wouldn't have encountered before.

Sure, there could be a genetic component to it but lots of folks are just lucky til they aren't.
posted by We put our faith in Blast Hardcheese at 3:35 PM on June 10, 2022 [2 favorites]

To your question about low-level exposure to small viral loads or attenuated viral loads, etc: I will say that I find this line of reasoning compelling and maybe even hopeful, but don't think there's any solid evidence yet because it is by nature a terribly hard thing to study.

We have all kinds of evidence with other viruses of the human immune system learning and providing effective defense based on various types of partial/less harmful exposures.

It's not unreasonable to suspect you may have had some benefit from this, but it would be unwise to take any specific action based upon that suspicion. (I am a biologist but not that kind of biologist.)
posted by SaltySalticid at 6:09 PM on June 10, 2022 [2 favorites]

Response by poster: > it would be unwise to take any specific action based upon that suspicion

Ah, don't worry, this is 100% curiosity.
posted by The corpse in the library at 6:10 PM on June 10, 2022 [2 favorites]

There was this study that showed a high level of asymptomatic infection for grocery store workers.
posted by Violet Hour at 10:17 PM on June 10, 2022

So just to throw this in here as anecdata, you really can't know if you have had Covid or not, even if you have tested.

My husband has had Covid 3 times now (he works in an unsafe environment where masking and social distancing does not happen and we only got the vaccine relatively late in South Africa).

Each time he'd been exposed to a person who had rested positive for Covid, he had all the classic symptoms, and his doctor confirmed that he had Covid.

Two of the three times, he never tested positive. I also got Covid, and I never tested positive.

The tests are not that reliable. So it's not really possible to say, with confidence, that you never had Covid.
posted by Zumbador at 10:32 PM on June 10, 2022

I was in the same situation you are (masked, at first in a cloth mask, then later in an N95, in public situations, double vaccinated and double boosted, never got it) until about a month ago, when I got a mild case. My spouse, to my knowledge, has never had it but he has been almost completely isolated due to stage 4 cancer. I suspect the earliy variants were less infectious.
posted by Peach at 6:28 AM on June 11, 2022

Best answer: You've had a stroke of good luck.

The odds are not unusual for someone taking precaustions to avoid infection for the duration of the pandemic to this point. The odds are not unusual for someone to have had an asymptomatic case, or multiple asymptomatic cases. On both or either counts, raise a glass to the gods of good fortune.

Signed, an epidemiologist who is currently extremely, fantastically unwell from his second COVID infection (but thank heaven for those vaccines, right? I'm typing this mild complaint to you from my bed rather than intubated in an ICU so good on you for all the precautions you've taken. Long may they continue.)
posted by late afternoon dreaming hotel at 11:12 AM on June 11, 2022 [3 favorites]

There have been a couple studies now showing that blood type could be a factor.
posted by aspersioncast at 7:13 PM on June 11, 2022

I don't know if this anecdote is useful for your purposes, but we are still learning from and about those with immunity from the 1918 flu. I imagine we'll have some similar discoveries about SARS-CoV-2 in the coming years.

In my family, my grandmother and my great-grandfather (her father) appeared to completely avoid the 1918 flu. They lived in a house full of infected family members, often sleeping in the same bed as those with active infections. Some had milder cases and other had fevers so high their hair fell out. I'm not aware of any isolation or masking and medical care was a homegrown affair (a visiting doctor might have come through now and then). Perhaps they were never infected, but it does seem more likely that they had a mild case that built enough immunity to carry them through.

I'm terribly glad to have far more information and preventative measures at my disposal, but it is interesting to consider all the ways our bodies and diseases are amazing and confounding.
posted by annaramma at 10:28 PM on June 11, 2022 [1 favorite]

My sister is an MD who has treated many many Covid patients. She has not gotten it even though her husband, her kids, their partners, and their children have all had it.
posted by mareli at 8:56 AM on June 26, 2022

Response by poster: Update: I got COVID two months after asking this. Yup, jinxed myself.
posted by The corpse in the library at 1:22 PM on September 12, 2022 [3 favorites]