The aim of a vaccine is to 'prime' the immune system with a concoction that will stimulate it into making its memory cells or antibody. Then if the bacteria or virus is encountered later in life the immune system can react quickly and effectively.

You might want to look at "The Immune System" before you read the rest of this!

The first time we meet a particular germ, whether it is a bacteria, virus, fungi, yeast or even larger bugs such as parasites, the immune system has to start from the beginning. However, thanks to memory cells, that live for a long time, if the same micro-organism is met later in life the immune system can leap into action very quickly and usually defeats the germ before it causes an illness.

Earlier generations had to suffer an illness to gain this immunity to later attacks. Now there are vaccines for many of the diseases that our grandparents had to endure.

The immune system has different ways to fight different germs. There are different types of white cells that have different roles and some help others to work more efficiently.

The B cells are the family of cells that make antibodies. However sometimes they need help from another group of cells that belong to the T cell family.

Children with 22q11 deletion usually have normal B cells but their T cell count may vary from normal to absent. As they grow up most 22q11 deletion children form enough T cells to help the B cells but until there are enough around then the vaccine would be useless.

The T cells that can help the B cells have a 'marker' and are often called CD4 cells. Doctors will wait until the level of CD4 cells is high enough, usually around a count of 400 cells/µL of blood before giving some vaccines.

A blood test may be taken at a later time to check if the patient has responded to the vaccine and can be considered immune to that particular disease.

Vaccines are made in various ways.

Some may be made from a product of a germ that causes the effects of the illness: Tetanus germs produce a poison that causes the muscles to go into 'spasm' and are unable to relax. The vaccine used is directed against this poison or 'toxoid' instead of the actual germ.

Others may be made from dead germs that the B cells can still recognise.

A few are made from a harmless but live germ that is a close relative to a nasty germ (like measles) that can cause a disease. This type of vaccine MUST NEVER be given to a patient with an immune system that cannot work properly.

Thus, vaccines fall into two major groups:

Inactivated vaccines

Those prepared from killed or purified fragments of bacteria or viruses that can fool the immune system into thinking it has met the real germ.

In the routine vaccines these are:

• combined Diphtheria, Pertussis (whooping cough), Tetanus, (Hib - Haemophilus influenzae type b) and polio (DTaP/IPV/Hib)

• Meningitis C (Men C)

• Cervical Cancer (Human papillomavirus - HPV)

• Pneumonia (Prevenar - PCV)

Live Vaccines

contains a variation of the germ that does not cause disease in people with a healthy immune system. The vaccine variant must share enough similarities with its infectious relation that a response to the variant in the vaccine protects against the nasty germ.

In routine vaccines these are:

• combined Mumps, Measles and German Measles (Rubella) – (MMR)

This is the UK 2011 Routine Immunisation Schedule published by the Dept of Health

Two Months Old (two injections)

• Diphtheria, tetanus, whooping cough, polio and Hib

• Pneumonia (Prevenar - PCV)

Three months old (two injections)

• Diphtheria, tetanus, whooping cough, polio and Hib (DTaP/IPV/Hib)

• Meningitis C (MenC)

Four Months Old (three injections)

• Diphtheria, tetanus, whooping cough, polio and Hib(DTaP/IPV/Hib)

• Meningitis C (MenC)

• Pneumonia (Prevenar - PCV)

Between 12 and 13 months of age (three injections)

• Hib and meningitis C (Hib/MenC)

• Pneumonia (Prevenar - PCV)

• Measles, mumps and rubella (MMR)

(within a month of the first birthday)

Three years four months to five years old (two injections)

• Diphtheria, tetanus, whooping cough and polio (DTaP/IPV or dTaP/IPV)

• Measles, mumps and rubella (MMR)

Girls aged 12 to 13 years old (a course of three injections)

• Cervical Cancer (Human pappilovirus - HPV)

Thirteen to 18 years old (one injection)

• Tetanus, diphtheria and polio (Td/IPV)

So Children routinely have received these vaccines by these ages:

• By four months: Three doses of DTaP/IPV/Hib. Two doses of PCV and MenC.

• By 13 months: A booster dose of Hib/MenC and PCV and the first dose of MMR.

• By school entry: Fourth dose of DTaP/IPV or dTaP/IPV and the second dose of MMR.

• Before leaving school: Fifth dose of Td/ Fifth dose of Td/IPV and, for girls, three doses of HPV vaccine.

Other Vaccines that may be offered:

• TB (Tuberculosis) – (BCG) – This is now only usually offered if there is a high risk of contracting the disease or if a family member has had it within the last 6 months - it is no longer routinely included in the UK schedule for teenagers, so for most patients will not raise a question. BCG should not be given to any infants with significant T lymphocyte abnormalities. For individual cases where BCG is being considered, advice should be sought from an immunologist.

• Chicken Pox Vaccine (varicella) is discretionary, but is safe to give if the CD4 T lymphocyte count is above 400 cells/µL of blood.

Vaccination advice summary:

Many parents are worried about vaccinating their children, especially with the MMR vaccine. However the advice given by Max Appeal's panel of immunologists is very clear and this is the summary.

• Everyone with 22q deletion should be seen by an immunologist at least once to have their blood analysed.

• The normal vaccination schedule should be followed as long as there is CD4 T lymphocyte count of more than 400 cells/ml of blood.

• Primary immunisations should be given to all babies without delay.

• A very small number of people with 22q deletion will have very low T cell counts (this is a severe immunodeficiency) and the immunisations those rare patients there may be no benefit because the vaccines will not stimulate antibody production.

• There may be follow up blood tests to see how well the person has responded to the vaccines, if there is poor response then further monitoring by an immunologist may be needed.

• For the majority of children (who will have a CD4 T lymphocyte count above 400 cells/µL of blood), immunisation with the measles, mumps and rubella (MMR) vaccine is safe. So all those children should receive MMR.

• Currently in the UK the chicken pox vaccine (varicella) use is discretionary, but is safe to give if the CD4 T lymphocyte count is above 400 cells/µL of blood.

• TB (BCG) immunisation is no longer routinely included in the UK schedule for teenagers, so it will generally not raise a question. BCG should not be given to any babies with significant T lymphocyte abnormalities. For individual cases where BCG is being considered, advice should be sought from an immunologist.

Finally:

Speak to your doctor if you are at all uncertain about your child's immunisation programme.

Your concerns are valid. Make sure you are happy before you proceed, that isn't being over-anxious!