COVID-19 can weaken your immune system, both during acute infection and for months afterward. The virus depletes key immune cells, triggers prolonged inflammation, and leaves some people more vulnerable to secondary infections. How much it affects you depends on the severity of your infection, whether you were vaccinated beforehand, and whether you develop long COVID.
How the Virus Depletes Immune Cells
When SARS-CoV-2 takes hold, it triggers a massive inflammatory response sometimes called a cytokine storm. This flood of inflammatory signals shifts the body’s metabolism toward a more acidic state, which suppresses the growth of T cells, the white blood cells responsible for hunting down infected cells and coordinating your immune response. Worse, the inflammatory environment actively pushes T cells toward programmed cell death. Up to 85% of people with severe COVID-19 show significant drops in T-cell counts in their blood.
The virus may also kill T cells directly, though the exact mechanism is still being worked out. The result is a temporary but meaningful gap in your immune defenses during and after infection, leaving you less equipped to fight off other pathogens at the same time.
Immune Changes That Last Months
The damage doesn’t fully resolve when your COVID symptoms clear. Dendritic cells, which act as the immune system’s scouts by detecting threats and alerting T cells, remain depleted for at least seven months after infection. A study published in Cellular and Molecular Immunology found that two important types of dendritic cells stayed at reduced levels seven months out, regardless of whether patients had been hospitalized. In people who were hospitalized, the ability of these cells to produce a key antiviral signal (interferon alpha) was still not restored at that point either.
T cells also show signs of exhaustion well after the infection clears. In people with long COVID, T cells display elevated levels of exhaustion markers like PD-1 and CTLA4 at eight months compared to people who fully recovered. The good news is that these exhaustion markers do fade. By 24 months, PD-1 and TIM-3 levels on T cells no longer differ between long COVID and recovered groups, suggesting the immune system does gradually reset.
Higher Risk of Other Infections
The immune disruption translates into real-world vulnerability. A large study comparing COVID-19 patients to people who tested negative found that even those with mild, non-hospitalized infections had a 17% higher rate of new infectious illness diagnoses afterward, including bacterial, fungal, and viral infections. For respiratory infections specifically, the risk jumped 46%. Hospitalizations for infectious illnesses were 41% higher in the COVID group.
To put this in perspective, researchers also compared people hospitalized for COVID against people hospitalized for seasonal flu. The COVID group still came out worse: 24% more likely to be hospitalized again for an infectious illness and 35% more likely to develop sepsis. This isn’t just a general consequence of being sick. Something about COVID-19 specifically leaves the immune system more compromised than a comparable respiratory infection.
How Long COVID Keeps the Immune System Off Balance
For people who develop long COVID, immune dysfunction becomes a defining feature rather than a temporary aftereffect. Research published in Nature Immunology in 2025 identified a clear pattern: chronic inflammation paired with immune exhaustion persisting more than 180 days after the initial infection. People with long COVID showed elevated levels of multiple inflammatory markers, including IL-6 and components of a key inflammatory pathway called JAK-STAT, alongside reduced signals for T-cell activation and differentiation.
This creates a paradox. The immune system is simultaneously overactive (chronic inflammation, elevated complement and coagulation signals) and underperforming (exhausted T cells that respond poorly to threats). The inflammatory signaling correlates directly with T-cell exhaustion, meaning the more inflamed the system stays, the less capable the T cells become. It’s not that the immune system shuts down. It’s stuck in a dysfunctional loop where it’s burning energy on inflammation while losing its ability to mount targeted responses.
Is This Like Measles “Immune Amnesia”?
You may have seen comparisons to measles, which is known to cause “immune amnesia,” a phenomenon where the virus infects long-lived immune memory cells in the bone marrow and essentially erases the body’s library of antibodies against other diseases. This can set someone back years in immune protection, even undoing the benefits of previous vaccinations.
COVID-19 does not appear to work the same way. Measles directly infects the cells that store your immune memory. SARS-CoV-2 primarily disrupts the immune system through inflammation, cell exhaustion, and depletion of frontline responders rather than erasing existing antibody memory. The mechanisms are different, and the consequences are different. COVID weakens your current immune capacity rather than wiping out your historical defenses. That said, some researchers have noted that if measles circulates widely alongside COVID, the combination of immune amnesia from measles and immune exhaustion from COVID could compound each other’s effects on population-level immunity.
Vaccination Reduces the Immune Damage
Prior vaccination meaningfully blunts the immune disruption caused by a breakthrough COVID infection. Research published in Science Translational Medicine found that vaccinated people who caught COVID showed a less activated, less inflammatory profile in monocytes and natural killer cells compared to unvaccinated people with primary infections. Essentially, vaccination prevented the kind of immune overactivation that drives much of the downstream damage.
This matters because it’s the excessive inflammatory response, not just the virus itself, that depletes T cells and exhausts the immune system. By keeping that inflammatory surge in check, vaccination appears to protect not only against severe disease but against the lingering immune dysfunction that follows. The study also found sex-specific differences in how vaccination shaped the immune response, though the protective effect held across groups.
Autoimmune Risks After Infection
Beyond temporary immune suppression, COVID-19 also increases the chance that the immune system turns on the body’s own tissues. A 2025 meta-analysis covering 97 million individuals found that COVID-19 was associated with a 49% increased risk of developing a new autoimmune condition. Out of 23 autoimmune diseases studied, 17 showed statistically significant increases after COVID infection.
The highest risks were for antiphospholipid syndrome (a clotting disorder, with roughly double the risk), a type of blood vessel inflammation called ANCA-associated vasculitis (also about double), mixed connective tissue disease, and immune thrombocytopenic purpura, a condition where the immune system destroys platelets. These aren’t common conditions to begin with, so a doubled risk still represents a small absolute number of people. But the pattern is consistent: COVID can push a dysregulated immune system toward attacking the body itself, particularly in people who may have been genetically predisposed.
What Recovery Looks Like
For most people, the immune system does recover. T-cell exhaustion markers normalize by about two years. The heightened infection risk is most pronounced in the months following COVID and gradually diminishes. But the timeline isn’t uniform. People with more severe infections, those who weren’t vaccinated, and those who develop long COVID face longer and deeper immune disruption. Repeated infections may compound the effect, though long-term data on cumulative immune impact from multiple COVID infections is still being gathered.
The practical takeaway is straightforward. COVID-19 does weaken your immune system, through a combination of T-cell depletion, dendritic cell loss, chronic inflammation, and immune exhaustion. For most people this is temporary. For some, particularly those with long COVID, it persists for many months. Vaccination before infection is the most effective way to limit the damage.