Worry that a flu shot will stir up an autoimmune condition is one of the most common reasons people with these diseases skip it.1PubMed. Barriers and facilitators to influenza and pneumococcal vaccine hesitancy in rheumatoid arthritis: a qualitative study For the standard flu shot, though, large studies across several autoimmune diseases have mostly found no rise in flares. The more useful comparison is with catching the flu itself, which carries more risk than the shot for people whose immune systems are already working against them.
What the Large Studies Show About Flares
A UK study of nearly 15,000 people with rheumatoid arthritis, spondyloarthritis or lupus who got the flu shot found no link with flares or other harmful effects.2Annals of the Rheumatic Diseases. Association between inactivated influenza vaccine and primary care consultations for autoimmune rheumatic disease flares: a self-controlled case series study using data from the Clinical Practice Research Datalink Each person’s flare rate in the weeks after the shot was set against their own rate at other times, so differences like age, disease severity and medicines didn’t muddy the result. If the shot truly caused flares, the extra ones would bunch up just after vaccination. None did.
Rheumatology’s main US guideline says the vast majority of studies show no increase in flares after a flu shot.3PubMed Central. 2022 American College of Rheumatology Guideline for Vaccinations in Patients With Rheumatic and Musculoskeletal Diseases It recommends the standard flu shot whether your disease is quiet or active.4PubMed Central. 2022 American College of Rheumatology Guideline for Vaccinations in Patients With Rheumatic and Musculoskeletal Diseases
Some people do feel worse afterward, which is why the fear persists. Flares come and go on their own in these diseases, so some will land in the weeks after any shot by chance. Flu season also brings colds and stress, which can trigger flares too, and only a comparison of timing across thousands of people can sort that out. One person’s experience can’t.
One pooled analysis found that people with RA reported more side effects after the flu shot than people without RA, mostly mild ones.5PubMed. Is rheumatoid arthritis associated with reduced immunogenicity of the influenza vaccination? A systematic review and meta-analysis Normal reactions are a sore, red arm, tiredness or mild aches that last a day or two. A flare looks like your usual disease pattern returning: swollen joints, rash or gut symptoms that don’t fade within a couple of days.
If you can’t tell which one you’re dealing with, write down the day symptoms began and what they feel like. If they match your usual pattern and haven’t eased after a few days, call your specialist team.
How a Vaccine Could in Theory Trigger the Immune System
The main theory is that a piece of a virus or vaccine resembles one of your own proteins, so immune cells aimed at it may also attack you.6IMAJ. Influenza vaccine and autoimmunity Your immune cells learn to recognize a target by its shape, and occasionally a viral fragment has a shape close enough to one of your own proteins to confuse them. For most autoimmune diseases, this remains a hypothesis rather than an established cause.
It has been confirmed in one place. With flu and the sleep disorder narcolepsy, researchers found the same immune cells reacting to a flu protein and a brain protein.7News Center. Mistaken identity: Influenza/narcolepsy autoimmunity link confirmed That shows mimicry can be real, which is why scientists take the theory seriously and keep checking. But that link involved a specific flu strain and setting, not the routine flu shots studied in the large flare studies.
A second theory is that a strong immune response to a vaccine can switch on nearby immune cells that weren’t its target.8PubMed Central. SARS-CoV-2 vaccine-triggered autoimmunity: Molecular mimicry and/or bystander activation of the immune system If some of those neighbors already react against your own tissue, being woken up could in theory push them to act. In animal experiments this happened even without the extra immune-boosting ingredients some vaccines add.9PubMed Central. Bystander activation of irrelevant CD4+ T cells following antigen-specific vaccination occurs in the presence and absence of adjuvant
A plausible mechanism isn’t the same as a real risk. Infections trigger these same processes, usually more strongly than a vaccine does. The real test is whether flares rise in actual patients, and the large studies say they don’t.
What We Know for Each Condition
In a nationwide lupus study, health problems were no more common in vaccinated than unvaccinated patients.10PubMed Central. Effects of annual influenza vaccination on morbidity and mortality in patients with Systemic Lupus Erythematosus: A Nationwide Cohort Study Across nearly 2,000 vaccinated lupus patients, 32 had mild flares and 2 had severe ones.11PubMed Central. Immunogenicity and Safety of Influenza Vaccination in Systemic Lupus Erythematosus Patients Compared with Healthy Controls: A Meta-Analysis Lupus flares on its own, with or without any shot. In one comparison, vaccinated patients had 3 flares over 12 weeks versus 6 among unvaccinated patients, a difference too small to mean anything.12PubMed. Influenza virus vaccination of patients with systemic lupus erythematosus: effects on disease activity
A major MS study found the flu shot did not raise the chance of a relapse in the following two months.13PubMed. Vaccinations and the Risk of Relapse in Multiple Sclerosis A relapse means new or worsening neurological symptoms, such as numbness, vision trouble or weakness, lasting more than a day or so. If you have MS and notice new symptoms after a shot, they are worth reporting to your neurology team, but the shot is not a likely cause.
A UK-wide study found no link between the flu shot and Crohn’s or colitis flares in the 90 days after.14PubMed Central. Uptake, safety and effectiveness of inactivated influenza vaccine in inflammatory bowel disease: a UK-wide study Among people on immune-suppressing or biologic drugs given a swine-flu vaccine, about 96 to 97 in 100 had no flare four weeks later.15PubMed. H1N1 vaccines in a large observational cohort of patients with inflammatory bowel disease treated with immunomodulators and biological therapy
Several studies of children with juvenile arthritis found no change in disease activity and no relapses after the flu shot, only mild arm pain and brief joint aches.16PubMed Central. Influenza vaccination in patients with juvenile idiopathic arthritis under different treatments: safety and immune response17PubMed Central. Prospective surveillance study of acute respiratory infections, influenza-like illness and seasonal influenza vaccine in a cohort of juvenile idiopathic arthritis patients One small study of 31 children saw flares in about 1 in 8 within a month and about 1 in 3 over six months.18PubMed. Safety and efficacy of influenza vaccination in a prospective longitudinal study of 31 children with juvenile idiopathic arthritis Juvenile arthritis flares often anyway, and that study’s long window catches ordinary ups and downs, so the larger picture stays reassuring. If your child has juvenile arthritis, note any flare symptoms and tell the rheumatology team at the next visit.
Some conditions, like polymyalgia rheumatica, have only individual case reports rather than large studies. If your condition isn’t among the well-studied ones, ask your specialist.
Should You Pause Your Medicines Around the Shot
Methotrexate, a common weekly RA drug, can blunt the body’s response to vaccines.19PubMed Central. Treatment with Biologicals in Rheumatoid Arthritis: An Overview Briefly stopping it after the flu shot improves how well the shot works.20PubMed. Effect of Temporary Methotrexate Discontinuation on Vaccine Immunogenicity and Disease Flare in Rheumatoid Arthritis: A Systematic Review A one-week pause gave the same protection as a two-week pause, with about 7 in 10 people responding well either way.21rheumatology.org. Study Finds Holding Methotrexate for One Week after Flu Vaccine May Be as Effective as a Two-Week Hold The cost is flares: about 1 in 22 people flared in the month after a one-week pause, versus about 1 in 8 after a two-week pause.22PubMed Central. A Multicenter, Prospective, Randomized, Parallel‐Group Trial on the Effects of Temporary Methotrexate Discontinuation for One Week Versus Two Weeks on Seasonal Influenza Vaccination in Patients With Rheumatoid Arthritis So if a pause is advised, one week is usually enough.
In practice, you get the shot and then skip only the next weekly methotrexate dose, resuming on your usual day the following week. Agree the plan with your rheumatologist before the shot so you both know the dates. If you notice joint swelling or stiffness during the pause, report it to your team rather than waiting it out.
Skipping the pause can also be a reasonable choice. If your disease is hard to control, staying on methotrexate may matter more, and the shot still gives some protection without a pause. The decision balances your flare history against your infection risk.
Other drugs are simpler. TNF blockers such as adalimumab or etanercept, and tocilizumab, do not reduce flu shot response.23PubMed Central. Treatment with Biologicals in Rheumatoid Arthritis: An Overview24Medical Clinics of North America. Vaccinations in Patients with Rheumatic Disease: Consider Disease and Therapy Rituximab does weaken vaccine response,25PubMed Central. Treatment with Biologicals in Rheumatoid Arthritis: An Overview so if you take it, ask about timing the flu shot relative to your infusion. And never stop or skip a medicine for a vaccine without your prescriber’s say-so.
Which Flu Vaccine to Choose
Most flu shots are inactivated, meaning they contain killed virus or pieces of it that cannot cause infection. Because of that, the shot cannot cause flu, even in someone with a weakened immune system. These vaccines are considered safe for people with autoimmune rheumatic disease, though they may work a bit less well on immune-suppressing drugs.26PubMed. Vaccination recommendations for adult patients with autoimmune inflammatory rheumatic diseases
The nasal spray flu vaccine is different. It contains weakened but living virus, and it is generally not given to people on immune-suppressing treatment.27PubMed. Vaccination recommendations for adult patients with autoimmune inflammatory rheumatic diseases Ask for the injected shot, not the spray. At the pharmacy, mention your immune-suppressing drugs and confirm it is an injection.
Some flu shots for older adults contain an added ingredient to strengthen the response. An expert review found no convincing evidence that these added ingredients cause autoimmunity.28PubMed. Safety of vaccine adjuvants: focus on autoimmunity Still, one reported case described a severe polymyalgia rheumatica flare in a 70-year-old after such a shot.29PubMed Central. Relapse of polymyalgia rheumatica following adjuvanted influenza vaccine: A case-based review If you have polymyalgia rheumatica and are offered a boosted shot, ask your doctor whether a non-boosted shot suits you better.
Guillain-Barré Syndrome and the Flu Shot
Guillain-Barré syndrome (GBS) is a condition where the immune system attacks nerves, causing weakness that usually starts in the legs. It occurs in about 1 to 2 of every 100,000 people in the US each year for any reason.30Centers for Disease Control and Prevention. Guillain-Barré Syndrome and Flu Vaccine If the flu shot adds risk, it’s about 1 to 2 extra cases per million doses.31Centers for Disease Control and Prevention. Guillain-Barré Syndrome and Flu Vaccine When it happens, it appears within about 6 weeks of the shot.32vaccinesafety.edu. Can a Flu Shot Cause an Autoimmune Flare?
Flu itself is the bigger trigger. Flu infection has been linked to about 17 GBS cases per million infections, versus about 1 per million vaccinations.33Global Autoimmune Institute. Infection vs. Vaccination: Which Raises Autoimmune Disease Risk? Getting vaccinated likely lowers your overall GBS risk by preventing flu.
Tingling or weakness that starts in the feet and legs is the typical early sign of GBS. Weakness that spreads upward or appears on both sides of the body is a warning sign. Trouble walking, breathing or swallowing means emergency care right away. Tell the doctors about your recent flu shot, because the timing helps them with diagnosis. If you’ve had GBS within 6 weeks of a flu shot before, discuss your options with your doctor.
Why the Flu Itself Is the Bigger Threat
Autoimmune reactions are far more common after infections than after vaccines.34Global Autoimmune Institute. Infection vs. Vaccination: Which Raises Autoimmune Disease Risk? People on immune-suppressing drugs are more likely to have serious flu complications such as pneumonia. A flu infection can also set off a flare directly, since fever and illness stress alone can push one along. It may force you to pause your medicines while sick, which leaves your disease less controlled just when your body is under strain. Even if the shot works a bit less well on your medicines, partial protection still lowers your chance of serious illness.
A few steps help beyond the shot. Ask household members to get vaccinated too. Contact your doctor early if flu symptoms start, since antiviral pills work best within two days. And ask whether you need other vaccines such as pneumococcal.
What to Do If You Feel Worse After Your Shot
Mild aches in the first one to two days usually pass on their own. Rest and simple pain relief your doctor has approved are usually enough. Track your symptoms for a day or two, and use your usual flare plan if you have one, since it was written for this kind of situation.
If joint swelling, rash or gut symptoms persist beyond a few days, contact your specialist. In one trial, fewer than 1 in 10 needed extra pain medicine after the shot, even with a medicine pause.35PubMed Central. A Multicenter, Prospective, Randomized, Parallel‐Group Trial on the Effects of Temporary Methotrexate Discontinuation for One Week Versus Two Weeks on Seasonal Influenza Vaccination in Patients With Rheumatoid Arthritis
If you had a rough reaction, prepare for next year. Write down what happened and when, and discuss whether timing around your medicines could be adjusted.