Immunisation Side Effects

Overview

Immunisation side effects are the expected reactions your body can have after a vaccine. They are not the disease the vaccine protects against. Most are mild, like a sore arm or a short fever, and go away on their own.

Mild side effects are common. Serious side effects are rare.

Anyone can get them, from babies to older adults. Children are more likely to get a fever or be fussy after some vaccines. Older adults may notice a sore arm, tiredness, or aching. Severe reactions can affect anyone but are very uncommon.

Symptoms

Common symptoms

• Soreness, redness, or swelling where the needle went in
• Mild fever
• Feeling tired or sleepy
• Headache
• Muscle aches
• Feeling sick or off your food
• Swollen glands

Symptoms in children

• Fever
• Crying or being fussy
• Sleepiness or poor feeding
• Sore, red, or swollen injection site
• A hard lump at the injection site that can last a few weeks

Symptoms in older adults

• Sore arm
• Tiredness
• Headache or muscle aches
• Mild fever
• Feeling dizzy or faint around the time of injection, especially if anxious

Causes

Main causes

• The immune system responds to the vaccine, which can cause temporary redness, soreness, or fever.
• The injection itself can irritate the skin and muscle.
• Some vaccines are more likely to cause fever or tiredness than others.
• Anxiety or needle fear can cause dizziness or fainting around the time of the injection.

Risk factors

• Having had a similar reaction before
• Certain vaccines, especially some live or combination vaccines
• Young age, especially babies and young children for fever
• A history of fainting with needles
• Being very anxious about injections

When to see a doctor

See a doctor urgently if:

• Call your local emergency number immediately for trouble breathing, swelling of the face or throat, collapse, or a seizure.
• Get same-day medical advice for a fever in a baby under 3 months, a fever that is high or not settling, severe injection-site swelling, or a child who is very drowsy, floppy, or difficult to wake.
• Ask for urgent help if you feel very unwell, dizzy, or faint after leaving the clinic.

Book a routine appointment if:

• Mild side effects that last more than a few days or get worse
• A lump at the injection site that is still there after several weeks
• You are worried about a reaction or need advice about future vaccines
• You want to report a suspected side effect

Diagnosis

There is usually no test. A doctor or nurse recognises side effects from the timing, the symptoms, and the vaccine you had. They may check you over to rule out other causes, especially if symptoms are severe or unusual.

Tests that may be done

• Usually no tests are needed.
• A review of your vaccine record and the time symptoms started.
• Blood tests or allergy tests only if a serious reaction is suspected.
• A physical check of the injection site and vital signs if you feel unwell.

What to expect at your appointment

You will be asked what vaccine you had, when, and what symptoms you noticed. Most people are reassured and sent home with advice. Suspected side effects may be reported to a vaccine safety scheme so that vaccines can be monitored.

Treatment

Most side effects need no treatment. The aim is to make you or your child comfortable while the body settles. If you have a serious reaction, emergency care is needed.

Self-care at home

• Rest if you feel tired.
• Drink plenty of fluids.
• Put a cool, clean cloth on a sore or swollen injection site.
• Wear loose clothing over the area.
• Gently move the arm or leg if it is comfortable.
• Ask a pharmacist what fever or pain relief is suitable for your age; never give a child medicine without checking first.

Medical treatments

A pharmacist, nurse, or doctor can advise on age-appropriate medicine for fever or pain. They may suggest simple comfort measures. For a severe allergic reaction, emergency treatment is given in hospital. There is no specific medicine that prevents all side effects.

When is surgery considered?

Surgery is not used to treat immunisation side effects.

Living with this condition

You can usually carry on with normal daily activities if you feel well. If you have a fever or feel tired, take it easier for a day or two. Keep an eye on young children after their vaccines.

Lifestyle tips

• Plan a quiet day after vaccination if you can.
• Keep your vaccine record handy.
• Know the signs of a serious reaction and when to get help.
• Tell your nurse or doctor about any previous reaction before future vaccines.

Diet and exercise

Eat and drink normally. Fluids are especially helpful if you have a fever. Gentle movement is fine; avoid hard exercise if you feel unwell or feverish.

Mental health and emotional wellbeing

It is normal to feel anxious, especially if you or your child had a reaction or you fear needles. Tell your nurse or doctor so they can help. Slow breathing and a calm, quiet space can help with needle worry. If anxiety feels overwhelming or you are in crisis, contact your local crisis service or emergency number.

Prevention

You cannot prevent all side effects, but you can make them easier. Tell the nurse about past reactions, stay calm and hydrated, and plan a quiet day after vaccination. Serious reactions cannot be predicted, but clinics are trained to manage them.

Vaccines

Vaccines are given to prevent serious diseases. Side effects are usually a sign the immune system is responding, not a sign that the vaccine has caused the disease. The benefits of vaccination usually outweigh the risk of side effects.

Screening programmes

There is no screening test for vaccine side effects. Your vaccination record and a conversation with your healthcare provider are the best way to plan safely.

Complications

If left untreated

• Most side effects settle without treatment.
• A rare severe allergic reaction can be life-threatening if not treated quickly.
• A rare injection-site infection can happen if the area becomes very red, hot, and painful.
• Fainting can lead to a fall or injury.
• Febrile seizures can happen in young children with fever, but they usually do not cause lasting harm.

Long-term outlook

The outlook is very good. Most people feel back to normal within a few days, and serious reactions are rare. Vaccination remains an important way to protect against serious diseases.

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