Vaccines and safety

How do vaccines work?

Vaccines contain either a greatly weakened form of the bacterium or virus that causes a disease, or a small part of it. When the body detects the contents of the vaccine its immune system will be primed to make the antibodies (substances that fight off infection and disease) required to fight off the infection.

If your child comes into contact with the infection, the immune system will recognise it and be ready to protect him or her by producing the right antibodies. Because vaccines have been used so successfully in the UK, diseases such as diphtheria have almost disappeared from this country.

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What vaccines should I get?

For information on individual vaccines, visit The vaccines explained

To browse vaccines according to the age of your child, visit When to immunise?

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How do we know that vaccines are safe?

Years of extensive laboratory and clinical tests are undertaken during a vaccine's development.

Before a vaccine is put into general use it has to be licensed. In order to be granted a license, the manufacturers have to demonstrate its quality, safety, and efficacy in preventing the particular disease that it is intended for.

Before clinical trials can be started the relevant regulatory authorities and Ethics Review Committees (external link) have to give their approval.

The Medicines and Healthcare products Regulatory Agency (MHRA) (external link) monitors the safety of vaccines through the Yellow Card Scheme (external link).

The information collected through the Yellow Card Scheme is constantly reviewed by independent experts and used to inform national immunisation policy decisions.

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Will my baby have any side effects from the injection?

Some babies may have side effects. They may:

  • have redness, swelling or tenderness where they had the injection (this will slowly disappear on its own)
  • be a bit irritable and feel unwell
  • have a temperature (fever).

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What is a fever?

A fever is a temperature over 37.5oC. Fevers are quite common in young children, but are usually mild. If your child’s face feels hot to the touch and they look red or flushed, he or she may have a fever. You could check their temperature with a thermometer.

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Is fever common after an immunisation?

Fever can be expected after any immunisation, but is more common when the MenB vaccine is given with the other routine vaccines at 2 and 4 months of age. Fever is much less common when the MenB booster is given at 12 months. For more information about fever after an immunisation read our What to expect after immunisation: babies and young children sheet

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Is it safe to give babies paracetemol?

Although paracetamol is safe in very young children, the current advice for non-vaccine fever is that no more than two doses should be given to babies aged 2–3 months, without seeking the advice of a GP or pharmacist. This is to ensure that fever which may be due to a serious infection in babies of this age is quickly diagnosed and treated.

After MenB immunisation, giving paracetamol will reduce the risk of fever, irritability and discomfort for your baby (such as pain at the site of the injection). It is important that a total of three doses of infant paracetamol are given to babies after each of their first two MenB immunisations to reduce the chances of fever. The first dose of infant paracetamol should be given just before or just after the routine immunisations. You may already have infant paracetamol at home. If you don't, you can get the paracetamol from your pharmacist before your baby's immunisations are due.

For more information about giving your baby paracetamol after MenB immunisation, read our What to expect after immunisation: babies and young children sheet

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How to treat a fever

Keep your child cool by:

  • making sure they don’t have too many layers of clothes or blankets on (remove clothes)
  • switching down the house heating
  • giving them plenty of cool drinks (if you are breastfeeding, your child may feed more frequently) 

You don't need to put them in a bath, sponge them down or put them in front of a fan. There is no evidence that this will lower your child's fever.

A dose of infant paracetamol may help reduce your child’s fever. Read the instructions on the bottle very carefully. You may need to give a second dose four to six hours later.

If you are worried about your child, trust your instincts.

Speak to your doctor or call NHS 24 on 111 (freephone). Call the doctor immediately if, at any time, your child has a temperature of 39oC or above, or has a fit. If the surgery is closed and you can’t contact your doctor, trust your instincts and go to the emergency department of your nearest hospital.

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What are fits?

Fits are also called seizures or convulsions. Some are associated with fever and some are not. In the first five years of a child’s life, the most common type of fit is caused by fever (this may be called a ‘febrile seizure’ or ‘febrile convulsion’). Sometimes immunisations are followed by a fever that may cause a febrile seizure. Most children who have febrile seizures recover fully.

When a seizure occurs within a short time after immunisation, it might not have been caused by the vaccine or the fever. It could be due to an underlying medical condition. If your baby has a fit after an immunisation, contact the doctor. He or she may refer you to a specialist for advice about further investigation and future immunisations. If the surgery is closed or you can’t contact the doctor, trust your instincts and go straight to the emergency department of your nearest hospital.

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I’m worried that my baby may have allergies. Can he or she still have the vaccine?

Yes. Asthma, eczema, hay fever, food intolerances and other allergies do not prevent your child having any of the vaccines in the routine childhood immunisation programme. If you have any questions, speak to your doctor, practice nurse or health visitor.

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Are some babies allergic to vaccines?

Very rarely, children can have an allergic reaction soon after immunisation. This reaction may be a rash or itching affecting part or all of the body. The doctor or nurse giving the vaccine will know how to treat this. It is not a reason to withhold further immunisations.

Even more rarely, children can have a severe reaction within a few minutes of the immunisation, which causes breathing difficulties and can cause the child to collapse. This is called an anaphylactic reaction. A recent study has shown that only one anaphylactic reaction occurs in about a million immunisations. The people who give immunisations are trained to deal with anaphylactic reactions and children recover completely with treatment.

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Last reviewed on 19 April 2016

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