Vaccinations are used to stimulate your body's natural defences to try and reduce the chances of you catching certain infections.

There are three main types of vaccine:

• live attenuated vaccines, which use minute quantities of the live virus or bacteria which causes the infection which has been changed (attenuated) so that it will not give the infection but will stimulate the immune system to develop antibodies in the blood which will protect against the infection.
• inactivated vaccines which use minute doses of dead virus or bacteria to stimulate immunity.
• detoxified toxins, which use traces of chemicals produced by the virus or bacteria to stimulate immunity.

Cancer and its treatment can affect your immune system in a number of ways. Some cancers, particularly lymphomas and leukaemias, may reduce the effectiveness of your body's natural defences and it is currently recommended that anyone who has had a lymphoma or leukaemia should always avoid live attenuated vaccines. Surgery seldom has any effect on the immune system. Radiotherapy often has a mild temporary effect on the immune system but this is unlikely to be troublesome except for people who have had whole body irradiation. Chemotherapy, however, can often have quite a major effect on the immune system, reducing the body's defences against infection for some months during and after treatment.

If either the cancer or its treatment have reduced the effectiveness of your immunity then live attenuated vaccines should be avoided. But inactivated vaccines and detoxified toxins are quite safe, although if your immune system is not working normally they may not be as effective in preventing infection.

Live vaccines include those against measles, mumps, rubella, yellow fever, BCG (to protect against tuberculosis) and the oral forms of polio and typhoid vaccine.

The current recommendations are that patients who have had steroid therapy in the last three months or chemotherapy in the last six months should not have these vaccines.

Inactivated vaccines and detoxified toxins include those against diphtheria, tetanus, whooping cough, influenza, hepatitis A, hepatitis B, rabies, cholera and the injectable form of polio and typhoid vaccine. These vaccines can safely be given after chemotherapy but may not offer as much protection against infection as normal in the first six months after treatment.

The type of vaccinations you might need for your holiday will depend on where you are going. When you have found out from your travel agent what is recommended then you should get your doctor's advice on what is best for you.