Reassurance on vaccines and allergy

By Anna Sayburn

BMJ Group News

What do we know already?

Very occasionally, we hear about people having severe, sudden allergic reactions to medicines or vaccines. These reactions are called anaphylaxis, or anaphylactic shock, and happen when the immune system overreacts to a usually harmless substance, causing swelling, breathing difficulties, and heart problems.

Because anaphylaxis is so rare, it’s not possible to tell reliably how often it happens during clinical trials of vaccines. Even very large trials would not be big enough to get a good understanding of this.

To get a more reliable understanding of the numbers, researchers contacted specialists across the UK and asked them to report any cases of anaphylaxis in a child after vaccination, between September 2008 and September 2009.

What does the new study say?

Only 15 cases were reported, and only seven cases were confirmed as anaphylaxis. None of the cases followed routine early childhood vaccination. There were reports of anaphylaxis with the single measles vaccine, and the HPV, meningitis, hepatitis A, and typhoid vaccines. All children made a full recovery from the anaphylaxis. The estimated rate of anaphylaxis was 12 reactions for every 100,000 single measles vaccine doses given, and one reaction for every million HPV vaccine doses given.

It’s important to remember that around 5.5 million routine infant vaccinations were given to children during the period studied, and there were no reports of anaphylaxis from this programme. The routine vaccination programme includes the combined measles, mumps, and rubella (MMR) vaccine, not the single measles vaccine.

How reliable is the research?

The research is based on a monthly survey of paediatricians that has a very high response rate (more than 90 percent). Although it is possible that some cases of anaphylaxis might have been missed if the child had not been referred to a paediatrician for treatment, or for assessment afterwards, the researchers say this is unlikely. The results - showing a very low level of reactions compared to the number of vaccinations - are in line with research from other countries, and are likely to be reliable.

What does this mean for me?

This study provides reassurance that severe allergic reactions to vaccination are extremely rare. Several of the children who had an anaphylactic reaction had previously suffered a severe allergic reaction. If your child has had a severe allergic reaction before, it’s a good idea to tell the doctor or nurse before they give your child a vaccine. They may need to have their vaccines in a specialist centre.