The chickenpox (varicella) vaccine

In Ireland, chickenpox is a very common childhood disease. Although usually mild, it can be a serious disease, especially for people with weak immune systems (such as those receiving chemotherapy) and pregnant women. Chickenpox is caused by the varicella zoster virus - a member of the herpesvirus family - which is spread very quickly between infected people.

Chickenpox vaccines contain 'live-attenuated' varicella zoster. Because the vaccine is live, you can develop some symptoms of the disease you are being vaccinated against (though this doesn't happen very often), but the symptoms are much milder - for example, about 2% of children develop a handful of blisters after receiving the vaccine, rather than the usual 200-500 blisters that develop during a dose of chickenpox. There is a small chance of passing on the infection if you develop blisters following vaccination - this is extremely rare, but it is a good idea to stay away from vulnerable people (such as those with weak immune systems) while you have the rash.

The first vaccinations against chickenpox took place in Japan in the 1970s. Vaccination is now routine in some countries, and many schools and childcare facilities ask for evidence of immunity against chickenpox - that they have either been vaccinated against the virus that causes chickenpox, or have had the disease - before the children are allowed to attend.

In Ireland, the VARIVAX vaccine (produced by Sanofi Pasteur MSD) has been available since 1997, and is recommended to be given in one or two doses to children over 12 months old (it is not recommended for babies under 9 months old). However, because the vaccine is not included in the HSE vaccination schedule in Ireland, parents have to pay for this privately - your GP will be able to advise you about the price and how long it will take to order the vaccine.

There are other chickenpox vaccines available worldwide, including a measles, mumps, rubella and varicella (MMVR) combination vaccine which has been available in the USA since 2005. However, these alternatives are not yet licensed for use in Ireland. There are also vaccines available to prevent shingles in adults (available privately in Ireland, for adults). Shingles is a very painful condition caused by a reactivation of the virus that causes chickenpox. It can develop in people who have had chickenpox at some point, usually those who are over 50 years of age (it is extremely rare in children).

Most common side effects are mild and temporary. They are a result of the child's immune system responding to the vaccination, and making antibodies that will protect the child in the future. Most side effects will ease after a day or two and any discomfort can be treated with over-the-counter medicines such as paracetamol or ibuprofen (ask your pharmacist for medicine appropriate for your child's age).

Before getting the vaccination, speak to your doctor if your child has been sick or 'off form' over the past few days. Illness can reduce the effectiveness of a vaccine. The nurse or doctor administering the vaccine will check your child’s temperature first, to see if they may have any other infections or illnesses.

Common side effects that are usually no cause for concern: soreness, redness or swelling at the injection site, high temperature, mild rash or a few small bumps and irritability.

Other rarer side effects include headache, conjunctivitis (eye infection), cough and runny nose, diarrhoea and vomiting, tiredness, and seizures. These side effects are rare and have been reported in very few children.

Remember that the benefits of receiving vaccines that protect your child from serious diseases hugely outweigh any mild side effects from vaccination.

If you are concerned about your child, contact your doctor or local hospital for advice.

Allergies to substances within vaccines can occur, though they are very rare (they happen in fewer than 1 in 10,000 people receiving the vaccine). An allergic reaction to a vaccine would happen quickly - probably before you left the GP's surgery. Signs of an allergic reaction may include itchy skin, rash, shortness of breath and swelling of the face or tongue.

Before getting the vaccination, speak to your doctor if your child has experienced any allergic reactions previously.

If you are concerned about your child, contact your doctor or local hospital for advice.

Vaccines are tested exhaustively before they are provided to the public (it normally takes 10-15 years to develop a new vaccine). VARIVAX (chickenpox vaccine produced by Sanofi Pasteur MSD) was licenced for use in the USA in 1995. Clinical trials were carried out initially on over 5,000 children (clinical trials are used to assess the safety of the vaccine and to collect data on possible side effects, such as those listed above), and the vaccine is now used routinely in many countries.