MS is often described as an autoimmune disease, which means the immune system attacks the body’s own tissues. Understanding what this involves can help explain why certain things matter more with MS, including winter colds, flu vaccination, and COVID boosters.

Understanding the immune system can help you make sense of your disease-modifying therapy, understand why some infections affect you more, and plan ahead each winter.

This article explains how the immune system works, what changes in MS, and what that means for protecting yourself during flu season and beyond.

Key Takeaways

• How the immune system normally works
• What happens in the body during MS
• Why infections can affect MS symptoms
• Which vaccines are considered safe and recommended with MS
• How to plan vaccination and winter care with your healthcare team

A Quick Tour of the Immune System

The immune system protects the body by finding and stopping invaders such as bacteria, viruses, and fungi. It has two main parts.

The first is the innate immune system, which acts quickly. It responds to signs of a problem and raises the alarm, but it is not very specific to particular threats.

The second is the adaptive immune system. These cells, including B cells and T cells, take longer to respond, but they learn to recognise specific threats and remember them. This memory is the reason vaccines work.

In a healthy immune system, these two parts work together, responding to threats while leaving the body’s own tissues alone.

What Goes Wrong in MS

In MS, the immune system mistakenly targets the body’s own tissue. Some specialist cells, mainly certain T cells and B cells, identify myelin, the protective coating around nerves, as a threat. They cross into the brain and spinal cord and attack myelin as if it were a foreign invader.

This leads to inflammation, damaged myelin, and disrupted nerve signals. It is what produces MS lesions on an MRI and, over time, the symptoms of MS.

Researchers do not fully understand why this happens. A combination of factors appears to contribute, including genetics, certain viral infections (particularly Epstein-Barr virus), low vitamin D, smoking, and patterns linked to geographic latitude.

How MS Treatments Work with the Immune System

Every disease-modifying therapy (DMT) acts on the immune system in some way. Some reduce the activity of certain T cells, some reduce certain B cells, and some prevent immune cells from crossing into the brain. Each approach has different effects, including on the general risk of infection.

This is why your neurologist will ask about your vaccination history, and why vaccines are sometimes recommended at particular times around starting a new medication. The aim is to keep protection in place where the immune system still needs it.

Why Infections Can Affect MS

Many people with MS notice that a cold, the flu, or a urinary tract infection makes their symptoms worse. This is known as a pseudo-relapse. Existing symptoms return or feel worse, not because MS is actively causing new damage, but because a raised body temperature and immune activation can slow nerve signals that are already affected.

A true relapse can also be triggered by significant infections, particularly viral ones. This is one reason infection prevention is given more attention for people with MS than for the general population.

Flu Season and MS: What to Know

Australian winters bring influenza, colds, RSV, and ongoing COVID activity. For people with MS, this is an important time to consider protection.

The flu vaccine is safe and recommended with MS. Large studies and clinical guidelines support annual flu vaccination for people with MS. Research also indicates that people with MS generally develop a good immune response to the flu vaccine, including most of those on DMTs.

The nasal flu spray is generally avoided. This is a live-attenuated vaccine and is not recommended for people with MS, particularly those on immune-modifying medication. The standard injectable flu vaccine is the recommended option.

COVID vaccines are recommended. Keeping up with boosters helps reduce the risk of severe illness and hospitalisation.

Timing matters with some DMTs. Certain medications, such as ocrelizumab, rituximab, or fingolimod, work best when vaccines are given at particular intervals. Your neurologist or MS nurse can help plan this.

Live vaccines are usually not suitable. For people on immune-suppressing DMTs, live vaccines, such as yellow fever or the Zostavax shingles vaccine, are generally avoided. Non-live alternatives are available for most of these. Shingrix, for example, is a non-live shingles vaccine.

Practical Ways to Stay Well Through Winter

• Have your annual flu vaccination, which is free for many Australians with chronic conditions through the National Immunisation Program
• Keep up with COVID boosters as recommended
• Wash your hands often, particularly after outings or contact with others
• Where possible, avoid close contact with people who have active respiratory infections
• Rest well, eat well, and keep warm
• See your GP early if you think you are becoming unwell, particularly if you are on a high-efficacy DMT
• Keep your vitamin D levels within range (your GP can test this)

If distance makes it hard to see your GP, telehealth can often be used to assess and treat minor infections, so you do not have to wait until symptoms become more serious.

Summary

MS is an autoimmune condition in which the immune system mistakenly targets myelin in the brain and spinal cord. Understanding this helps explain how treatments work and why winter infections can sometimes worsen symptoms.

The flu vaccine, COVID boosters, and sensible winter hygiene are simple and effective tools. Planning vaccines around your DMT with your GP and neurologist, and treating infections promptly, can help you stay well through the colder months.

FAQs

Will the flu vaccine trigger an MS relapse? Research consistently indicates that the standard injectable flu vaccine does not increase relapse risk in people with MS.

Can I still get the flu if I have had the vaccine? Yes, although it is usually milder. The vaccine reduces severity, complications, and the risk of hospitalisation.

Should I avoid crowds during flu season? Avoiding all crowds is not necessary, but extra care during peak flu weeks can be sensible, particularly for people who are immunosuppressed.

Does a cold count as a relapse? No. A cold may temporarily worsen symptoms, known as a pseudo-relapse, but symptoms usually return to baseline once you recover. If they do not, it is worth speaking with your MS nurse.

Can I take antibiotics for infections while on a DMT? Yes. Prompt treatment of bacterial infections, particularly urinary tract infections, is important to help avoid symptom flares.

References

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2. Farez, M. F., Correale, J., Armstrong, M. J., et al. (2019). Practice guideline update summary: Vaccine-preventable infections and immunization in multiple sclerosis. Neurology, 93(13), 584–594.
3. Confavreux, C., Suissa, S., Saddier, P., et al. (2001). Vaccinations and the risk of relapse in multiple sclerosis. New England Journal of Medicine, 344(5), 319–326.
4. Loebermann, M., Winkelmann, A., Hartung, H. P., et al. (2012). Vaccination against infection in patients with multiple sclerosis. Nature Reviews Neurology, 8(3), 143–151.
5. Bjornevik, K., Cortese, M., Healy, B. C., et al. (2022). Longitudinal analysis reveals high prevalence of Epstein-Barr virus associated with multiple sclerosis. Science, 375(6578), 296–301.
6. Ciotti, J. R., Valtcheva, M. V., & Cross, A. H. (2020). Effects of MS disease-modifying therapies on responses to vaccinations. Multiple Sclerosis and Related Disorders, 45, 102439.