Has Covid messed with our immune systems?
China, immune debt, and the latest immunology data story
Last week, a scare around an undiagnosed cluster of pediatric pneumonia in China rippled through social media. This was coupled with reports of overwhelmed pediatric hospitals in certain regions. The WHO confirmed this isn’t likely due to some novel pathogen but rather a resurgence of our “regular” viruses, like flu.
As you may remember, the U.S. experienced a similar resurgence of flu and RSV last year (and still somewhat this year).
This has, nonetheless, reignited a discussion around “immunity debt” and whether Covid-19 infections make us immunocompromised.
“Immunity debt”
In the first 2-3 years of the pandemic, RSV and flu, for example, were incredibly suppressed due to pandemic control measures. This led to a new phrase: “immunity debt” or “immunity gap.”
It’s centered around an increasing “susceptibility” pool, or how many people are vulnerable to infection. During the emergency, more and more people became susceptible due to a lack of infection (or maternal antibodies), susceptible people were born, and recovered people died. Then, when restrictions were lifted and the “normal” viruses returned, there was a HUGE susceptibility pool leading to many infections. This resulted in more infections than in the pre-pandemic seasons, which caused crowded hospitals in China, for example.
The U.S.—which is one year ahead of China in lifting restrictions—still has higher than “normal” RSV infections. It will likely take a few years to re-synchronize viral dynamics, but the dramatic effect is less apparent every subsequent year. Below is my best attempt at visualizing this phenomenon.
While the term might be new to the public, this phenomenon has been seen before. For example, when sanitation improved, polio initially got much worse.
Immunocompromised after Covid-19 infections?
There has been discussion around whether anything else could be causing this rise in pediatric infections, like: Could there be more viral infections because Covid-19 is doing something weird with our immune systems?
This does happen with other viruses. HIV and measles are notorious for it, for example.
However, the case for Covid-19 is weak thus far:
T cells. Early in the pandemic, scientists found that the T cells expressed many markers that implied exhaustion (or low T-cell count). After more inquiry, it was clear the actual behavior of the T cells was still very much functional. Another concern was a drop in the blood’s T cell levels. But low counts can be attributed to T cells doing their job: leaving the blood and going to the tissues to fight off infections. This can happen after any infection, even with the common cold.
B cells. One paper argues that Covid-19 infections might harm B cell responses (i.e., our antibody factories). This hasn’t been reproduced. Also, the high antibody levels we see after vaccination and infections show our antibody factories are still working.
Epidemiological RSV data. One study has shown that children are at increased risk for RSV infections after a positive Covid-19 test. While this concerns us parents, there were many limitations. For example, the Covid-19 negative patients were not tested for SARS-CoV-2 antibodies. If severe RSV and Covid-19 share risk factors in young kids, this could lead to artifactual findings exaggerating the risk.
We certainly need more studies. But there are specific situations that are genuinely concerning regarding immunocompromise after Covid-19 infections:
Severe Covid-19 disease can cause you to develop antibodies against certain messengers (called cytokines like interferon), which can block critical messages from being sent, drastically reducing your ability to respond to infections. This is seen after critical pneumonia, too. The good news is that, now, these severe cases of disease are more rare, and in most people, this issue fades over time.
Some niche immune cells seem to change a lot after Covid-19 infection, but they are relatively minor populations, and the consequences to our overall health from these changes aren’t entirely clear. (Also, these data are all pre-vaccine.)
Neither of these states is common enough in young children to explain current epidemiological trends.
This is not to say that Covid-19 is something that we can just ignore—it comes with plenty of risks unrelated to what it may or may not do to the immune system (such as blood clots), and many still suffer from long Covid-19 for reasons we don’t fully understand.
Bottom line
We will continue to see “immunity debt” play out on a population level. Keep up to date on vaccines and take reasonable precautions against respiratory viruses. This will help keep both healthcare systems and ourselves as healthy as possible.
Love, YLE and EN
“Your Local Epidemiologist (YLE)” is written by Dr. Katelyn Jetelina, MPH Ph.D.—an epidemiologist, wife, and mom of two little girls. During the day, she is a senior scientific consultant to several organizations, including the CDC. At night she writes this newsletter. Her main goal is to “translate” the ever-evolving public health world so that people will be well-equipped to make evidence-based decisions. This newsletter is free, thanks to the generous support of fellow YLE community members. To support this effort, subscribe below:
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Please don’t contribute to what is already a veritable swamp of disinformation, Dr. Jetelina.
“Immunity debt” isn’t a thing, because we know that immune systems don’t get stronger with repeat exposure to viruses. Additionally, this idea doesn’t hold up under even the most piddling questions from a non-scientist like me, such as:
1) If this were true, why are states that never had masking/distancing/“school lockdowns” (like in the Southern states) still suffering major waves of illness? Shouldn’t they have been spared these so-called “catch-up” waves, since they have been letting viruses tear through populations this whole time? I live in Georgia, where masking was NEVER a thing— even in medical settings— and schools never had masking requirements and only closed for about 8 weeks in April-May 2020. And I know that many other states— Alabama, Mississippi, Florida, South Carolina, Texas, Arizona, Oklahoma, Kentucky all come to mind— were the same way. So, if one were to buy into the “immunity debt” idea, why are those states still seeing record illness levels?
2) Why are places like Sweden, which famously boasted about its refusal to lockdown, still recording high excess deaths?
3) Why are places like India— which occasionally tries to do the mask mandate thing but hasn’t been very consistent across its enormous population — still getting slammed with waves of COVID and other weird opportunistic infections?
4) We know that the astronauts lucky enough to go to space have to quarantine before a space trip (no hospitals up there) and those going to the ISS stay up there— in a disease-free environment— for months. We know that their bodies are subjected to extensive study and analysis upon their return— which is how we know about the effects of gravity on muscle and bone, for example— and not once in the last 50 years has anyone found an astronaut with “immunity debt” from lack of viral exposure. We also know that immune-naive babies are born every hour of every day of every year all over the world, and we don’t see crushing waves of illness as those little immune systems run up against pre-2020 viruses.
5) Why is this “immunity debt” phenomenon totally new in medical literature and never seen before 2021, and only to justify a “return to normal”? In fact, before 2021, public health officials’ position was that AVOIDING illness was the better way to go, instead of loudly courting repeat illness as they are now, in service to this “immunity debt” deity that they invented out of thin air.
Also, Dr. J, if your position is that the evidence is “thin” on COVID-induced immune dysregulation, then you’re not looking too hard. There are dozens of studies highlighting the effects on CD4, CD8, and T cells at this point.
Lymphopenia/lymphocytopenia, a lack of white blood cells to fight infection, is caused by several things— but even according to official statements from NIH and pharmaceutical company Merck, one of the main causes of that condition is a COVID infection.
I think there is a combination of factors at play, including temporary immunity debt from quarantine/previous infection prevention measures… but I think the additional argument that immune system dysregulation is occurring much more broadly than we would like to admit, needs to be considered. Here is a somewhat alarming counterpoint, but worth a read and discussion:
https://whn.global/scientific/covid19-immune-dysregulation/