Steroids can do either, and the difference often comes down to timing and the specific virus involved. Corticosteroids are powerful immune suppressors, and during a viral infection that means they can quiet a dangerously overactive immune response or they can kneecap the very defenses your body needs to clear the virus. The landmark RECOVERY trial during the COVID-19 pandemic illustrated both sides of this coin in a single disease: dexamethasone cut deaths by roughly a third in patients on ventilators, yet it appeared to increase the risk of death in patients who were not yet sick enough to need supplemental oxygen. That split result is not unique to COVID. Across viral infections, the evidence consistently points to the same uncomfortable truth: the answer depends on when, how much, and which virus.
Why Steroids Cut Both Ways
Corticosteroids dial down the immune system broadly. That includes the inflammatory pathways responsible for fever, swelling, and tissue damage, but it also includes the antiviral machinery your body relies on to fight infection. In lab and animal studies, glucocorticoids suppress interferon production, which is one of the first-line chemical signals your immune system uses to contain viral spread. Fluticasone, a common inhaled steroid, reduced key antiviral interferons by as much as 75 to 85 percent in mice infected with rhinovirus, and virus levels in those animals climbed accordingly.1Nature Communications. Corticosteroid suppression of antiviral immunity increases bacterial loads and mucus production in COPD exacerbations The same pattern shows up in human airway cells: glucocorticosteroids knock down interferon-stimulated genes and let respiratory viruses replicate more freely.2Scientific Reports. Glucocorticosteroids enhance replication of respiratory viruses: effect of adjuvant interferon
This is the core problem. During the early phase of most viral infections, your body needs those interferon signals to limit how far the virus spreads. Suppressing them with steroids during that window can give the virus a head start. But in the later phase of certain severe infections, the immune response itself becomes the threat. Runaway inflammation, sometimes called a cytokine storm, can damage lungs, blood vessels, and organs far more than the virus alone would. In that scenario, reining in the immune system is exactly the right move.
COVID-19 and the Dexamethasone Story
The clearest evidence for steroid benefit in viral infection came from the RECOVERY trial, one of the largest randomized studies conducted during the pandemic. Among patients sick enough to need mechanical ventilation, dexamethasone reduced 28-day mortality from about 41 percent to about 29 percent. Patients on supplemental oxygen also saw a meaningful survival benefit.3PubMed. Dexamethasone in Hospitalized Patients with Covid-19 A later retrospective study confirmed the pattern and found that the benefit extended to at least one year of follow-up, with the greatest effect in patients on non-invasive ventilation.4PubMed Central. The impact of dexamethasone on short- and long-term mortality in hospitalized COVID-19 patients: a retrospective study
But the same RECOVERY trial showed something sobering in patients who were not on any respiratory support at the time they received steroids: the death rate was actually higher in the dexamethasone group than in usual care. A separate study of hospitalized COVID patients not receiving intensive respiratory support found an even sharper signal. Patients on no supplemental oxygen who received dexamethasone had a 76 percent increased risk of death at 90 days compared to those who did not receive it.5PubMed. Dexamethasone in hospitalised COVID-19 patients not on intensive respiratory support
Timing within the course of illness mattered too. An observational study of patients with mild COVID found that starting systemic corticosteroids within the first seven days of symptom onset was an independent risk factor for progressing to low oxygen levels. Patients who received steroids before day seven progressed to hypoxia at more than twice the rate of those who received them on day seven or later.6Drug Discoveries & Therapeutics. Role of systemic corticosteroids in preventing hypoxia among patients with mild COVID-19: An observational study The likely explanation is that early steroids blunted the antiviral immune response during the phase when the body was still trying to control viral replication, while later steroids arrived after the immune-mediated damage had become the dominant problem.
Why the Same Drug Fails in Influenza
If dexamethasone worked for severe COVID-19, a natural assumption is that it should work for severe influenza too. It does not. Observational studies of hospitalized influenza patients have consistently found that corticosteroid use is associated with increased risks of nosocomial pneumonia, critical illness, and death.7The Journal of Infectious Diseases. Host Immunomodulatory Interventions in Severe Influenza A critical appraisal of the literature concluded that corticosteroids are likely to increase overall mortality in severe influenza, a trend that held regardless of study quality or sample size, and were associated with higher rates of hospital-acquired pneumonia and longer time on ventilators.8PubMed Central. Corticosteroids for severe influenza pneumonia: A critical appraisal
The explanation likely comes down to differences in how the two viruses behave. Influenza replication peaks early and relies on a rapid interferon response to be contained. Suppressing that response with steroids during the critical early window gives the virus room to spread and invites secondary bacterial infections. Severe COVID, by contrast, tends to feature a delayed interferon response followed by a prolonged hyperinflammatory phase. Steroids that arrive during that later phase can tamp down the runaway inflammation without significantly interfering with viral clearance, because by that point replication has often already peaked.9PubMed Central. The role of corticosteroids in severe viral pneumonia: lessons from COVID-19 and influenza Systemic corticosteroids combined with antiviral therapy in influenza are not recommended, and the additional risk of opportunistic fungal infections adds another reason for caution.
RSV and Bronchiolitis in Children
For decades, clinicians hoped that steroids might help infants hospitalized with respiratory syncytial virus (RSV) bronchiolitis, given how much airway inflammation the disease causes. The evidence has been uniformly disappointing. A randomized trial of prednisolone in 147 infants with RSV found no effect on any measured outcome, either during the acute illness or at follow-up one month and one year later.10Pediatrics. Prednisolone Treatment of Respiratory Syncytial Virus Infection: A Randomized Controlled Trial of 147 Infants A separate trial of oral corticosteroids alongside inhaled bronchodilators in infants with mild-to-moderate bronchiolitis found identical clinical improvement between the steroid and placebo groups after three and seven days of treatment.11PubMed. Efficacy of corticosteroids in acute bronchiolitis: short-term and long-term follow-up Nebulized budesonide similarly showed no short- or long-term benefit for RSV bronchiolitis, with readmission rates, symptom resolution, and medication use all statistically indistinguishable between the steroid and placebo groups.12PubMed. Randomised placebo controlled trial of nebulised corticosteroids in acute respiratory syncytial viral bronchiolitis The collective message from these trials is clear enough that guidelines now recommend against routine steroid use in infant bronchiolitis.
Herpes Viruses and the Antiviral-Plus-Steroid Approach
Shingles, caused by the reactivation of varicella-zoster virus, is one viral condition where steroids do have a recognized role, though only when paired with an antiviral drug. A randomized trial comparing acyclovir plus prednisone to acyclovir alone or placebo found that the combination sped up crusting and healing and roughly tripled the rate at which patients returned to normal daily activities and stopped needing pain medication. However, prednisone did not reduce the risk of postherpetic neuralgia, the persistent pain that can linger for months after shingles.13PubMed. Acyclovir with and without prednisone for the treatment of herpes zoster. A randomized, placebo-controlled trial A separate trial confirmed that steroids reduced acute-phase pain in shingles patients but found no significant long-term difference in pain outcomes between groups.14PubMed. A randomized trial of acyclovir for 7 days or 21 days with and without prednisolone for treatment of acute herpes zoster The lesson: steroids can improve quality of life during the acute illness by reducing inflammation, but they do not fix the nerve damage that leads to chronic pain.
For herpes simplex encephalitis, a devastating brain infection, the picture is much less settled. Researchers have hoped that adding steroids to standard acyclovir treatment might limit the immune-mediated brain injury that causes long-term cognitive problems. A recent phase 3 trial of dexamethasone as an add-on to acyclovir in adults with herpes simplex encephalitis found no significant improvement in verbal memory scores at 26 weeks.15The Lancet Neurology. Dexamethasone as an adjunct to aciclovir in adults with herpes simplex virus encephalitis (DexEnceph): a multicentre, randomised, observer-blind, phase 3 trial A systematic review and meta-analysis also found that existing studies did not support a clear benefit, with one oft-cited small study reporting more deaths in the steroid-treated group despite a non-significant trend toward better outcomes in survivors.16PubMed Central. Steroids for the treatment of viral encephalitis: a systematic literature review and meta-analysis
Viral Myocarditis
When a virus inflames the heart muscle, the inflammation itself can be life-threatening. It seems intuitive that an anti-inflammatory drug would help. Yet a Cochrane review covering eight randomized trials found no significant difference in mortality between corticosteroid and control groups for viral myocarditis.17PubMed Central. Corticosteroids for viral myocarditis The trials were small and methodologically limited, so the evidence is not definitive in either direction. Animal data, however, sound a cautionary note: in a mouse model of acute viral myocarditis, prednisolone treatment significantly reduced survival and kept viral levels elevated far longer than in untreated controls, which had largely cleared the virus by the same time point.18Journal of the American College of Cardiology. Effects of prednisolone on acute viral myocarditis in mice This raises real concern that suppressing the immune response in the heart during active viral replication may allow the virus to do more structural damage.
Dengue Fever
Dengue is another infection where steroids have been tried repeatedly without convincing success. A Cochrane review of trials in both dengue-related shock and early-stage dengue found no detectable effect on mortality, the need for blood transfusions, development of shock, or severe bleeding. The review concluded the evidence is inconclusive, with low to very low quality across outcomes, and that there is insufficient evidence to recommend corticosteroids for dengue outside of a research setting.19PubMed Central. Corticosteroids for dengue infection Despite occasional clinical use in severe cases, the most that can be said is that steroid efficacy in dengue remains unproven.
Infectious Mononucleosis
Epstein-Barr virus, the cause of mononucleosis, can produce dramatic throat swelling that occasionally threatens the airway. Steroids are sometimes used in those situations to reduce the swelling quickly, and they do appear to work for that specific purpose.20PubMed Central. Airway compromise in infectious mononucleosis: a case report But for routine mono symptoms like fatigue, sore throat, and swollen glands, steroids are generally reserved only for life-threatening complications such as severe airway obstruction, dangerous drops in platelet counts, or severe hemolytic anemia. There is no strong evidence supporting their use for uncomplicated mono, and given the immune-suppressing effects, the risk-benefit ratio does not favor casual use against a virus that will resolve on its own in most people.
Hepatitis B Reactivation
One of the more insidious risks of steroid therapy has nothing to do with the infection being treated. People who carry hepatitis B, even those who seem to have recovered from a past infection, face a real danger of the virus flaring back to life when they take corticosteroids. Steroids reactivate HBV through two routes: they suppress the immune surveillance that keeps the virus in check, and they directly stimulate viral gene sequences. A retrospective study found that about 16 percent of HBV-positive patients on systemic corticosteroids for three months or more experienced viral reactivation, compared to roughly 3 percent on inhaled corticosteroids.21Frontiers in Medicine. Hepatitis B Virus Reactivation Associated With Therapeutic Interventions The risk climbs with dose: patients on the equivalent of more than 20 milligrams per day of prednisolone had reactivation rates around 14 percent, versus about 4.5 percent at lower doses. Even short, high-dose courses lasting less than a week can push the risk close to 10 percent when the peak dose exceeds the equivalent of 40 milligrams of prednisolone. A study of lupus patients on immunosuppressants found that nearly 40 percent of those who were HBV surface antigen-positive experienced reactivation, and over half of those had severe hepatitis flares.22PubMed. Increased risk of hepatitis B virus reactivation in systemic lupus erythematosus patients receiving immunosuppressants: a retrospective cohort study This is why screening for hepatitis B before starting steroid therapy and providing antiviral prophylaxis when needed is standard practice in many clinical settings.
Secondary Infections and Delayed Viral Clearance
Even when steroids save lives by calming a dangerous inflammatory response, they carry the cost of making the body more vulnerable to new infections. A large international registry study of hospitalized COVID patients found that early corticosteroid use was associated with roughly double the unadjusted risk of developing any secondary infection, including bacteremia, bacterial pneumonia, and septic shock. After adjusting for disease severity and other confounders, the overall association remained statistically significant, particularly for bloodstream infections and infections of unknown source.23Frontiers in Medicine. The association between early corticosteroid use and the risk of secondary infections in hospitalized patients with COVID-19: a double-edged sword
Steroids also appear to slow the body’s ability to clear the virus itself. A study of COVID patients found that high-dose corticosteroids (around 80 milligrams per day of methylprednisolone equivalent) significantly delayed viral shedding in a dose-dependent manner, while low-dose regimens did not show a statistically significant delay.24Clinical Infectious Diseases. High-dose but Not Low-dose Corticosteroids Potentially Delay Viral Shedding of Patients With COVID-19 This matters for infection control and for the patient: the longer a virus replicates, the more opportunities it has to mutate, and the longer the patient may be contagious.
Long-Term Recovery After Steroid-Treated Viral Infections
A natural question is whether steroids during an acute viral infection change the trajectory of recovery in the months and years afterward. A study from the RECOVER initiative evaluated whether corticosteroids given during acute COVID reduced the risk of developing long COVID in children and adolescents. It did not. There was no significant difference in long COVID risk between hospitalized children who received steroids and those who did not, and the same was true for outpatients.25PLOS One. Evaluation of steroids for acute COVID in the prevention of long COVID in children: an EHR and pediatric cohort study from the RECOVER initiative
That said, there is one area where steroids may offer a lasting advantage. A study of adults who had been treated with corticosteroids during acute COVID found that their lung function test results returned to baseline more rapidly than those of untreated patients, with both key measures of airflow improving at a faster monthly rate. The benefit held even in patients who were obese or had pre-existing lung disease.26PubMed Central. Long-term effect of corticosteroid treatment during acute COVID-19 infection on pulmonary function test results This fits with the idea that by limiting inflammatory lung damage in the acute phase, steroids may leave less scarring for the lungs to heal from later. Whether a similar pattern would hold in other viral pneumonias remains an open question, particularly given the opposite direction of the evidence in influenza.
Dose, Route, and the Question of Inhaled Steroids
Most of the evidence discussed so far involves systemic corticosteroids, meaning oral or intravenous drugs that circulate through the whole body. Inhaled corticosteroids, the kind used daily by millions of people with asthma and COPD, are a different story in terms of systemic exposure, though they are not entirely off the hook. A systematic review comparing inhaled and systemic corticosteroids in COPD exacerbations, many of which are triggered by respiratory viruses, found no significant differences in treatment failure rates or breathlessness, but inhaled steroids tended to cause fewer systemic side effects overall.27PubMed Central. Inhaled versus systemic corticosteroids for acute exacerbations of COPD: a systematic review and meta-analysis The trade-off was a higher rate of oral fungal infections with inhaled steroids versus more hyperglycemia with systemic ones. Lab studies do show that inhaled steroids like fluticasone can suppress antiviral interferon responses in airway cells and promote rhinovirus replication locally.28PubMed. Glucocorticoids impair type I IFN signalling and enhance rhinovirus replication For people on daily inhaled steroids for chronic lung disease, this creates an uncomfortable tension: the drug that controls their underlying condition may make respiratory viral infections somewhat harder to fight. Whether to adjust inhaled steroid use during a respiratory infection is a decision that depends on the individual’s disease severity and should be made with a physician, not unilaterally.
For systemic steroids, the meta-analysis data in COVID-19 reinforce that lower doses appear to provide a survival benefit while higher doses may carry more risk. A meta-analysis of randomized trials in severe COVID found a survival benefit at low corticosteroid doses but not at higher ones.29PubMed Central. Effects of different corticosteroid therapy on severe COVID-19 patients: a meta-analysis of randomized controlled trials Combined with the dose-dependent delay in viral clearance mentioned earlier, the message is that more is not better. The therapeutic window for corticosteroids in severe viral infection appears to be narrow: the right drug, at the right dose, at the right time in the disease course, for the right virus. Miss any of those variables and the same drug that saves lives in one context can make things worse in another.