Reinfection and Long COVID

Emily Oster

11 min Read Emily Oster

Emily Oster

Reinfection and Long COVID

Emily Oster

11 min Read

My mind, like many of ours, has been on worries other than COVID of late. But it’s also clear COVID is still very present, and for the first time in a while I found myself spiraling a bit on what to do about gathering with friends, mask-wearing, and indoor dining.

Part of my challenge, I’ve realized, is that I’m struggling with two aspects of the data. One is the risk of reinfection. I’ve had three shots and I’ve had COVID. And yet it does seem like people in that same boat are getting COVID again. How often? The second aspect is long COVID, discussed everywhere but something I’ve struggled to get my head around.

Today I’m going to offer — and sorry in advance that this is so long —- some data on both. The spoiler is that we do not have ideal evidence on either question so I’ll try to surface what we do have. I’m not going to offer much beyond the data today; I’ll try to be back in the next few weeks with some follow-up interpretation for paid subscribers.

The long COVID discussion is especially…long. I do urge you to read it all, but I’ll surface a summary paragraph:

My sense, putting this all together, is that persistent symptoms of fatigue, loss of smell, and coughing happen to a reasonable proportion of adults post-COVID, even after mild breakthrough infections. In some cases, these take months to resolve. But my sense is also that things like the CDC’s claims that COVID causes a dramatically elevated risk for pulmonary embolism and substance abuse disorder — the most significant disability and disease risks that they attribute to long COVID — are likely overstated by the lack of a reliable set of control individuals. This is triangulation, though. It’s informed triangulation, but others may well triangulate differently. 

Reinfection

How often will we get COVID?

We do not know for sure. What we do know is that COVID reinfection is possible and not uncommon over longer time scales. We also know that prior infection, vaccination, and (especially) both contribute significantly to protection against serious illness. This remains true over long time scales. But for someone like me with three shots and who had COVID in January, what’s the likelihood of getting it again — and when?

Reinfection is hard to measure reliably. It is getting harder because testing is getting less common and PCR testing even less so. Even if people rapid test at home, this may not get into an official system. A tremendously unscientific Instagram poll I ran the other day had 7% of about 20,000 people reporting having had COVID more than once since December. But who knows what that means and I didn’t ask the question well.

The most compelling (non-Instagram produced) data we have on this is from the UK through their ONS surveillance system. In their most recent data, they provide estimates of daily reinfection rates in the post-Omicron period. The way their data works is they effectively assume the first three months after infection are protected; they note this is somewhat arbitrary. It is possible to be reinfected within that window, but it looks unlikely (putting aside the Paxlovid rebound issue).

They then provide estimates of the daily rate of reinfection after that 90 days, based on the data they see and models they’ve developed. In the graph below, I converted these to monthly risks of reinfection each month post-infection. Because the ONS assumes the first three months are not “at risk,” I’ve put the first three months at zero.

This suggests a slightly less than 1% on average chance of reinfection each month, so perhaps a 5% risk of reinfection over six months. In their data, this is higher among unvaccinated people and those with an asymptomatic first infection. To be honest, based on what we’re seeing in the world, these numbers overall seem low (although they are considerably higher than in earlier waves).

It would be helpful, of course, to get more data on this going forward. In principle, survey data may be feasible if people are testing reliably. In reality, I’m not sure how much better we’ll do than the ongoing UK data. So thanks, UK, for picking up the slack.

Long COVID

This is an enormous topic, and I’m going to focus on the chaos of what we know about just one little piece of it — overall long COVID prevalence. Even still, this is not close to a comprehensive review.

Interestingly, although in general our evidence of COVID in children is worse than our understanding in adults, this is one area where we actually have slightly better data on kids. An example is one study that compares long-term symptoms of children who tested positive for COVID to those who tested negative in surveillance testing. They found extremely small differences in long-term symptoms, and any symptoms were mild. In general, studies of children that use appropriate control groups do not show a significant long COVID burden in this group.

When we turn to adults, it’s clear that long COVID is a more significant issue. But the estimates of the prevalence and the disease burden vary widely, for several reasons.

First, there is no standard definition of “long COVID”; definitions differ in what symptoms they include and in how long is “long.” If you define long COVID as any symptoms a month after infection, the rates will be higher than if you require three months. The more symptoms are included, the more likely it is that people have them. When we talk about long COVID, people sometimes imagine this only refers to debilitating cardiac and lung issues that persist for months and months, but a persistent sore throat for six weeks post-infection would also be part of this group.

Second, a large share of the studies we have on long COVID rely on selected samples, and most of them do not have controls. To be clear: such studies can be useful in helping us map out the picture of long COVID symptoms. But they aren’t as useful for evaluating prevalence. As an example, I found a quote from one review article stating: “In a very large study (2001 outpatients and 112 inpatients), only 0.7% of the population was symptom-free approximately 3 months after the initial infection.” That’s really scary, but in looking at the original article, we see this data is based on a sample recruited from a Facebook group for individuals who are suffering from persistent COVID symptoms. This is not useful for evaluating population prevalence.

A third issue is that even in large studies which do have a comparison group, it can be difficult to avoid the problem that those who get COVID may be different before COVID than others. An example of this is a new CDC study, which suggests approximately 20% of people 18 to 64 who have tested positive for COVID then develop long COVID, and 25% of those over 65. This study uses electronic medical record data and compares the rate of medical problems for individuals who were diagnosed (either inpatient or outpatient) with COVID to a comparison group who were not. The time period is 30 days to 365 days post-diagnosis, so this is intended to capture the long COVID period.

The study finds a higher rate of many illnesses in the COVID group: pulmonary embolism, substance abuse disorders, fatigue, heart failure, type 2 diabetes, and so on. Overall, 16% of the control group and 38% of the COVID group had a medical issue sometime in the year post-COVID, and the difference between these groups leads to the one in five long COVID headline numbers.

What makes this a bit hard to interpret is the authors are not able to adjust for any other differences across groups — including fairly basic things like gender, race, socioeconomic status, and other preexisting conditions. Since we know that some groups have been more vulnerable to symptomatic and serious COVID than others and that those characteristics are also associated with higher risks for other illnesses, it’s difficult to know how much of this to attribute to COVID. Most notably, obesity is associated with COVID and also with many of the long COVID symptoms identified. This isn’t to say that there isn’t significant evidence of long COVID in this study — notably, a persistent loss of taste and smell seems clearly COVID-associated — but just that the numbers are challenging to interpret.

A better version of this approach is this study, from September 2021, which looks for evidence of excess disease among people who had COVID relative to matched controls and compares this to the same approach for influenza. The authors find an excess long-term illness risk of 16 percentage points. This study has a lot to recommend it, although it is from an earlier period of the pandemic.

This raises the final issue: we have little sense of how long COVID intersects with vaccination or with COVID variants. There is a general sense that long COVID is less common with post-vaccine breakthrough infections, but we do not have precise information. Recently, a study based on Veterans Affairs data showed that individuals with breakthrough COVID infections were at a greater risk for long-term health issues than controls; the elevated risk was small but still present for those who were not hospitalized. But, again, it’s hard to separate COVID impacts from the other factors that raise the risk of having serious COVID in the first place.

Adding to all this complication, last week we got this new study, in Annals of Internal Medicine, which compared a sample of 189 people who had had COVID with 120 controls. Fifty-five percent of their COVID population reported persistent symptoms, relative to only 13% of the controls who hadn’t had COVID. This lines up with high rates of reported long COVID, but when the study looked at laboratory measures of inflammation, pulmonary activity, cardiac activity, cognitive function, and many others, they didn’t show any significant differences. This suggests we have a lot more to understand.

The bottom line is that if you’re wondering about the risk of long COVID after a mild to moderate Omicron breakthrough infection, we are in a bit of a data desert. We could triangulate — one study from spring 2021 shows the risk of persistent symptoms is 10 times lower after vaccination — so maybe we take our favorite estimate of 16% pre-vaccine and lower it to 1.6%. But none of this is direct. And we’re even worse off if we want to understand the degree of illness. Vaccination could lower the risk overall and decrease the severity of any long COVID symptoms which do occur. But we don’t really know.

My sense, putting this all together, is that persistent symptoms of fatigue, loss of smell, and coughing happen to a reasonable proportion of adults post-COVID, even after mild breakthrough infections. In some cases, these take months to resolve. But my sense is also that things like the CDC’s claims that COVID causes a dramatically elevated risk for pulmonary embolism and substance abuse disorder — the most significant disability and disease risks that they attribute to long COVID — are likely overstated by the lack of a reliable set of control individuals. This is triangulation, though. It’s informed triangulation, but others may well triangulate differently.

Our lack of data and understanding here is extremely problematic. We need more data, larger samples, and better designs. We need controls and better adjustments for pre-existing differences across groups. An example would be to use populations (i.e. college students) who are tested for surveillance reasons. Combining college-testing data with electronic medical records could provide insight into persistent symptoms in this population (and you could get some older people in there by including faculty and staff).

When we work to improve our data, a central goal should also be to distinguish among the forms of long COVID. What puts people at risk for longer-term disability versus persistent but more mild symptoms? Does Paxlovid or Evusheld help limit these risks? What treatments work?

I know there are those whose reaction here is to emphasize the need to return to more restrictions — masking, in particular. Without getting into the question of what should or shouldn’t be done, the reality is that COVID is going to continue to circulate. To the extent long COVID is a risk, it will continue to be one. Which means we need to understand it.

Covid-19 rapid antigen tests arranged in a pattern on a yellow background.

Feb 20 2023

12 min read

COVID-19: Where to Go from Here

A long-term view of the virus

Emily Oster
Covid-19 rapid antigen tests arranged in a pattern on a yellow background.

Oct 20 2022

9 min read

Should You Get the Bivalent Booster?

The latest on the risks and benefits of COVID vaccines boosters for older adults, pregnant people, and kids

Emily Oster
A line graph with pink, yellow, and blue dots representing life's ups and downs.

Aug 16 2022

3 min read

Wins, Woes, and Doing It Again

We have our first story from a dad! And it’s a good one. 10/10 —Girl Dad with Confidence Growing by Read more

Emily Oster
Covid-19 rapid antigen tests arranged in a pattern on a yellow background.

Aug 15 2022

8 min read

Updated CDC Guidelines for School and Child Care

NO QUARANTINES!!!

Emily Oster

Instagram

left right
Just eat your Cheerios and move on.

Just eat your Cheerios and move on. ...

The AAP’s guidelines recommend sleeping in the same room as your baby “ideally for the first six months.” However, the risk of SIDS is dramatically lower after four months, and the evidence in favor of the protective effect of room sharing is quite weak (both overall and even more so after four months). There is also growing evidence that infants who sleep in their own room by four months sleep better at four months, better at nine months, and even better at 30 months.

With this in mind, it’s worth asking why this recommendation continues at all — or at least why the AAP doesn’t push it back to four months. They say decreased arousals from sleep are linked to SIDS, which could mean that babies sleeping in their own room is risky. But this link is extremely indirect, and they do not show direct evidence to support it.

According to the data we have, parents should sleep in the same room as a baby for as long as it works for them! Sharing a room with a child may have negative impacts on both child and adult sleep. We should give families more help in navigating these trade-offs and making the decisions that work best for them.

#emilyoster #parentdata #roomsharing #sids #parentingguide

The AAP’s guidelines recommend sleeping in the same room as your baby “ideally for the first six months.” However, the risk of SIDS is dramatically lower after four months, and the evidence in favor of the protective effect of room sharing is quite weak (both overall and even more so after four months). There is also growing evidence that infants who sleep in their own room by four months sleep better at four months, better at nine months, and even better at 30 months.

With this in mind, it’s worth asking why this recommendation continues at all — or at least why the AAP doesn’t push it back to four months. They say decreased arousals from sleep are linked to SIDS, which could mean that babies sleeping in their own room is risky. But this link is extremely indirect, and they do not show direct evidence to support it.

According to the data we have, parents should sleep in the same room as a baby for as long as it works for them! Sharing a room with a child may have negative impacts on both child and adult sleep. We should give families more help in navigating these trade-offs and making the decisions that work best for them.

#emilyoster #parentdata #roomsharing #sids #parentingguide
...

It was an absolute pleasure to be featured on the @tamronhallshow! We talked about all things data-driven parenting and, in this clip, what I call the plague of secret parenting. To balance having a career and having a family, we can’t hide the fact that we’re parents. If mothers and fathers at the top can speak more openly about child-care obligations, it will help us all set a new precedent.

Watch the full segment at the link in my bio 🔗

#tamronhall #tamronhallshow #emilyoster #parentingsupport #workingparents

It was an absolute pleasure to be featured on the @tamronhallshow! We talked about all things data-driven parenting and, in this clip, what I call the plague of secret parenting. To balance having a career and having a family, we can’t hide the fact that we’re parents. If mothers and fathers at the top can speak more openly about child-care obligations, it will help us all set a new precedent.

Watch the full segment at the link in my bio 🔗

#tamronhall #tamronhallshow #emilyoster #parentingsupport #workingparents
...

Invisible labor. It’s the work — in our households especially — that has to happen but that no one sees. It’s making the doctor’s appointment, ensuring birthday cards are purchased, remembering the milk.

My guest on this episode, @everodsky, has come up with a solution here, or at least a way for us to recognize the problem and make our own solutions. I’ve wanted to speak with Eve for ages, since I read her book Fair Play. We had a great conversation about the division of household labor, one I think you’ll get a lot out of!

Listen and subscribe to ParentData with Emily Oster in your favorite podcast app 🎧

#emilyoster #parentdata #parentdatapodcast #parentingpodcast #householdtips #fairplay #invisiblelabor

Invisible labor. It’s the work — in our households especially — that has to happen but that no one sees. It’s making the doctor’s appointment, ensuring birthday cards are purchased, remembering the milk.

My guest on this episode, @everodsky, has come up with a solution here, or at least a way for us to recognize the problem and make our own solutions. I’ve wanted to speak with Eve for ages, since I read her book Fair Play. We had a great conversation about the division of household labor, one I think you’ll get a lot out of!

Listen and subscribe to ParentData with Emily Oster in your favorite podcast app 🎧

#emilyoster #parentdata #parentdatapodcast #parentingpodcast #householdtips #fairplay #invisiblelabor
...

Prenatal vitamins 💊 If there is any product that seems designed to prey on our fears, it’s this one. You’re newly pregnant and you want to do it right. Everyone agrees you need prenatal vitamins, so you get them. But do you want to be that person who just… buys the generic prenatal vitamins?

Good news: fancier vitamins are not better.  Folic acid is the most important prenatal ingredient. Iron (with vitamin C) and DHA are also nice to have. Other included ingredients have only weak or no evidence to support their use. (If you do not consume animal products, add B12, plus a few others depending on your diet.)

Vitamins are just vitamins. Any prenatal vitamin that contains these is enough. 

Comment “Link” for a DM to an article with everything you need to know about prenatal vitamins.

#emilyoster #parentdata #prenatalvitamins #pregnancydiet #pregnancytips

Prenatal vitamins 💊 If there is any product that seems designed to prey on our fears, it’s this one. You’re newly pregnant and you want to do it right. Everyone agrees you need prenatal vitamins, so you get them. But do you want to be that person who just… buys the generic prenatal vitamins?

Good news: fancier vitamins are not better. Folic acid is the most important prenatal ingredient. Iron (with vitamin C) and DHA are also nice to have. Other included ingredients have only weak or no evidence to support their use. (If you do not consume animal products, add B12, plus a few others depending on your diet.)

Vitamins are just vitamins. Any prenatal vitamin that contains these is enough.

Comment “Link” for a DM to an article with everything you need to know about prenatal vitamins.

#emilyoster #parentdata #prenatalvitamins #pregnancydiet #pregnancytips
...

When it comes to introducing your newborn to the world, timing matters. It’s a good idea to minimize germ exposure in the first 6-8 weeks; after that, it’s inevitable and, very likely, a good idea! This doesn’t mean you need to be trapped inside. The most significant exposure risks are from seeing other people at home — family, etc. These interactions are not infinitely risky, but they do pose more risk than a walk or a trip to the grocery store, since they involve closer interaction. Think simple and make sure everyone is washing their hands before holding the baby. 💛

#parentdata #emilyoster #newborncare #parentingadvice #parentingtips

When it comes to introducing your newborn to the world, timing matters. It’s a good idea to minimize germ exposure in the first 6-8 weeks; after that, it’s inevitable and, very likely, a good idea! This doesn’t mean you need to be trapped inside. The most significant exposure risks are from seeing other people at home — family, etc. These interactions are not infinitely risky, but they do pose more risk than a walk or a trip to the grocery store, since they involve closer interaction. Think simple and make sure everyone is washing their hands before holding the baby. 💛

#parentdata #emilyoster #newborncare #parentingadvice #parentingtips
...

The first edition of Hot Flash is out now! Comment “Link” for a DM to learn more about the late-reproductive stage.

There are times when we expect hormonal shifts. Our reproductive lives are bookended by puberty and menopause. We discuss those changes often because they are definitive and dramatic — a first period is something many of us remember clearly. But between ages 13 and 53, our hormones are changing in more subtle ways. During the late-reproductive stage (in your 40s), you can expect a lot of changes in your menstrual cycle, including the length and symptoms you experience throughout. It’s an important time in our lives that is often overlooked!

🔥 Hot Flash from ParentData is a weekly newsletter on navigating your health and hormones in the post-reproductive years. Written by Dr. Gillian Goddard, Hot Flash provides all of the information you need to have a productive, evidence-based conversation about hormonal health with your doctor.

#emilyoster #parentdata #hotflash #perimenopause #womenshealth

The first edition of Hot Flash is out now! Comment “Link” for a DM to learn more about the late-reproductive stage.

There are times when we expect hormonal shifts. Our reproductive lives are bookended by puberty and menopause. We discuss those changes often because they are definitive and dramatic — a first period is something many of us remember clearly. But between ages 13 and 53, our hormones are changing in more subtle ways. During the late-reproductive stage (in your 40s), you can expect a lot of changes in your menstrual cycle, including the length and symptoms you experience throughout. It’s an important time in our lives that is often overlooked!

🔥 Hot Flash from ParentData is a weekly newsletter on navigating your health and hormones in the post-reproductive years. Written by Dr. Gillian Goddard, Hot Flash provides all of the information you need to have a productive, evidence-based conversation about hormonal health with your doctor.

#emilyoster #parentdata #hotflash #perimenopause #womenshealth
...

There are plenty of reels telling you how to parent. Plenty of panic headlines saying that “studies show” what’s best for your kid. Even good data, from a trusted source, can send us into a spiral of comparison. But I want you to remember that no one knows your kid better than you. It’s important to absorb the research, but only you will know the approach that works best for you and your child. 💙

Now tell me in the comments: what’s a parenting move you’ve made recently that feels right to you?

#parentingcommunity #parentingsupport #parentingquotes #emilyoster #parentdata

There are plenty of reels telling you how to parent. Plenty of panic headlines saying that “studies show” what’s best for your kid. Even good data, from a trusted source, can send us into a spiral of comparison. But I want you to remember that no one knows your kid better than you. It’s important to absorb the research, but only you will know the approach that works best for you and your child. 💙

Now tell me in the comments: what’s a parenting move you’ve made recently that feels right to you?

#parentingcommunity #parentingsupport #parentingquotes #emilyoster #parentdata
...

Let’s talk about sex (after) baby! Today on the podcast, I was lucky enough to speak with @enagoski about her new book on sexual connection in long-term relationships. Especially after having kids, this is something many people struggle with. Emily tells us to stop worrying about what’s “normal” and focus on pleasure in its many forms.

Listen and subscribe to ParentData with Emily Oster in your favorite podcast app 🎧

#parentdata #parentdatapodcast #emilyoster #emilynagoski #comeasyouare #cometogether #longtermrelationship #intimacy #relationships

Let’s talk about sex (after) baby! Today on the podcast, I was lucky enough to speak with @enagoski about her new book on sexual connection in long-term relationships. Especially after having kids, this is something many people struggle with. Emily tells us to stop worrying about what’s “normal” and focus on pleasure in its many forms.

Listen and subscribe to ParentData with Emily Oster in your favorite podcast app 🎧

#parentdata #parentdatapodcast #emilyoster #emilynagoski #comeasyouare #cometogether #longtermrelationship #intimacy #relationships
...

Ever wondered if you can safely use leftover baby formula? 🍼 The CDC says to throw out unused formula immediately because of the risk of bacterial growth. However, research suggests that bacterial concentrations do not appreciably increase after 3, 12, or even 24 hours at refrigerator temperatures. Good news! This means there’s not a strong data-based reason to throw out formula right away if you store it in the fridge.

Comment “Link” for a DM to an article on another common formula question: should you throw away old formula powder?

#emilyoster #parentdata #babyformula #babyfeeding #parentingstruggles

Ever wondered if you can safely use leftover baby formula? 🍼 The CDC says to throw out unused formula immediately because of the risk of bacterial growth. However, research suggests that bacterial concentrations do not appreciably increase after 3, 12, or even 24 hours at refrigerator temperatures. Good news! This means there’s not a strong data-based reason to throw out formula right away if you store it in the fridge.

Comment “Link” for a DM to an article on another common formula question: should you throw away old formula powder?

#emilyoster #parentdata #babyformula #babyfeeding #parentingstruggles
...

What’s the most important piece of advice for new parents? Here’s one answer, but I want to hear from you! Share your suggestions in the comments ⬇️

#emilyoster #parentdata #parentingtips #parentingadvice #newparents #parentingcommunity

What’s the most important piece of advice for new parents? Here’s one answer, but I want to hear from you! Share your suggestions in the comments ⬇️

#emilyoster #parentdata #parentingtips #parentingadvice #newparents #parentingcommunity
...

What's in the bag of a Vagina Economist? 👀 Someone please tell me this looks familiar to you.

What`s in the bag of a Vagina Economist? 👀 Someone please tell me this looks familiar to you. ...

Comment ”link” for a DM to learn more about tongue ties 🔗

Breastfeeding is often difficult, especially at the start. For babies with tongue ties, many infants (and their moms) struggle to get the hang of a good latch. This can lead to painful nipples and to inefficient feeding, and then low weight gain.

So what does the data say about the increasingly common practice of cutting tongue-ties in infants to improve breastfeeding success? Several weeks ago, @nytimes published a long and quite scary article on this topic.

After diving into the data, here is what I found. There is limited evidence that frenotomy procedures improve breastfeeding efficacy and the harms of the procedure are minimal. Many women do report that it alleviates pain and helps them with breastfeeding. However, it should not be a first-line treatment for breastfeeding problems.

#parentdata #emilyoster #tonguetie #tonguetiebabies #breastfeedingsupport

Comment ”link” for a DM to learn more about tongue ties 🔗

Breastfeeding is often difficult, especially at the start. For babies with tongue ties, many infants (and their moms) struggle to get the hang of a good latch. This can lead to painful nipples and to inefficient feeding, and then low weight gain.

So what does the data say about the increasingly common practice of cutting tongue-ties in infants to improve breastfeeding success? Several weeks ago, @nytimes published a long and quite scary article on this topic.

After diving into the data, here is what I found. There is limited evidence that frenotomy procedures improve breastfeeding efficacy and the harms of the procedure are minimal. Many women do report that it alleviates pain and helps them with breastfeeding. However, it should not be a first-line treatment for breastfeeding problems.

#parentdata #emilyoster #tonguetie #tonguetiebabies #breastfeedingsupport
...

Tag a friend who needs to hear this 💛 For many choices in parenting, there is no one right answer. We can use research and data to make informed decisions, but ultimately, it won’t tell you what to do. Only you can decide what will be best for your kids and your family.

I’m here to remind you to take a deep breath and trust yourself. I’ll be here to support you along the way. 

Thank you to everyone who submitted videos, including:
@sarah.consoli
@jess_lynn627
@nicolevandenwills
@thedrblair
@ncbenedict29
@haleycimini
@iamkellysnodgrass
@calesse_smith
@garnet__gordon
@jencoopgaiser87
@danigirl18c
@jamielundergreen
@carly_comber
@thecelebratingmama
@emilyannbynum
@eeliz413

#emilyoster #parentdata #parentingadvice #parentingsupport #parentingquotes

Tag a friend who needs to hear this 💛 For many choices in parenting, there is no one right answer. We can use research and data to make informed decisions, but ultimately, it won’t tell you what to do. Only you can decide what will be best for your kids and your family.

I’m here to remind you to take a deep breath and trust yourself. I’ll be here to support you along the way.

Thank you to everyone who submitted videos, including:
@sarah.consoli
@jess_lynn627
@nicolevandenwills
@thedrblair
@ncbenedict29
@haleycimini
@iamkellysnodgrass
@calesse_smith
@garnet__gordon
@jencoopgaiser87
@danigirl18c
@jamielundergreen
@carly_comber
@thecelebratingmama
@emilyannbynum
@eeliz413

#emilyoster #parentdata #parentingadvice #parentingsupport #parentingquotes
...