Twinrix Paediatric is a vaccine. Vaccines work by ‘teaching’ the immune system (the body’s natural defences) how to defend itself against a disease. Twinrix Paediatric contains small amounts of inactivated hepatitis-A viruses and the ‘surface antigen’ (proteins from the surface) of the hepatitis-B virus. When a person is given the vaccine, the immune system recognises the viruses and surface antigens as ‘foreign’ and makes antibodies against them. In the future, the immune system will be able to make antibodies more quickly when it is exposed to the viruses. The antibodies will help to protect against diseases caused by these viruses.

The vaccine is ‘adsorbed’. This means that the viruses and surface antigens are fixed onto aluminium compounds, to stimulate a better response. The surface antigens of the hepatitis-B virus are produced by a method known as ‘recombinant DNA technology’: they are made by a yeast that has received a gene (DNA), which makes it able to produce the proteins.

Twinrix Paediatric is identical to the vaccine Twinrix Adult, which has been available in the European Union (EU) since 1996. The only difference between the two vaccines is the amount of vaccine in each vial or syringe. The active substances in Twinrix Paediatric and Twinrix Adult have been available in the EU for a number of years in separate vaccines: Havrix Adult for protection against hepatitis A and Engerix-B for protection against hepatitis B.