Babies A to Z

VACCINATION

Vaccination is the process in which a substance (antigen) is injected, swallowed or otherwise taken into the body in order to trigger a reaction in the immune system, which causes the production of proteins (immunoglobulins) known as antibodies. A very small number of the antibodies against a particular antigen remain in the body for many years, or for the rest of the patient’s life. While these antibodies remain, the body retains the memory of how to produce them, so that at a later time, if an antigen to which it has been previously exposed enters the body, the body can rapidly produce more antibodies to destroy it. This rapid response enables the body to defend itself against antigens that may be harmful.

All viruses and bacteria have proteins on their surface, which may act as an antigen to trigger an antibody response. This is the basis of vaccination. A harmless part of a virus (for example), or all of a killed virus, is introduced into a person to trigger an antibody response without causing the disease for which the virus is normally responsible. This then gives long-term immunity against the virus. The immune system sometimes needs several prompts by repeated doses of the antigen in order to obtain long term immunity. A patient whose immune system has responded appropriately to the vaccination so that they have immunity is said to have seroconverted (become seropositive). This means that the antibodies against the virus can be detected by the appropriate blood test. A small number of patients may not form adequate levels of antibodies in response to an antigen and are described as failing to seroconvert (they are seronegative).

Viruses are far simpler structures than bacteria, and as a result vaccines against viruses are far easier to produce than those against viruses, or even more complex parasites. The majority of vaccines available act against viruses, there are a few against bacteria, and none as yet against parasites, although research is continuing on a vaccine that will act against the malaria parasite.

For the same reason, once a person has had a viral infection (eg. chickenpox), they normally have lifelong immunity to that disease due to the antibody response that the first infection triggered in the patient.

Many other substances can act as antigens, including all types of cells, many chemicals, foods, dusts, pollens etc. In most vases the body recognises that these antigens are not harmful and has no, or a minimal reaction to these antigens, but in some people the antibody response to a particular antigen may become excessive to create an allergy reaction due to an over reaction by the immune system.

See also BACTERIA; VACCINATION OF CHILDREN; VACCINES; VIRUS

VACCINATION OF CHILDREN

Unless there are very good medical grounds not to vaccinate, all children should receive the full course of injections to protect them against tetanus, whooping cough and diphtheria; the HiB vaccine against Haemophilus influenzae B infections; the measles, mumps and rubella vaccine; hepatitis B vaccine; and the Sabin vaccine by mouth for polio. A chickenpox vaccine has been available since 2000 and is being steadily more widely used, a Meningococcal meningitis vaccine was introduced in 2002 and a Pneumococcal pneumonia vaccine in 2003. The risk of vaccination is infinitesimal, and when compared with the potential side effects of any one of these diseases, it is a far preferable course of action. Another person (adult or child) only has to breathe the infecting germs in the direction of a child and he or she may catch one of these dread diseases.

Tetanus is around us constantly in the soil. The bacteria causing this disease are carried by animals and are therefore not likely to be eradicated in the near future. The series of tetanus injections received as a child do not give lifelong immunity, and boosters are required every ten years, or more frequently if injury occurs.

Most young doctors have never seen a case of diphtheria. The incidence of this disease is now low, but older citizens may recall losing childhood friends to it. Diphtheria is still around though, and many children still catch the disease each year, and suffer the difficulty in breathing, and possible heart complications that can accompany it.

Whooping cough is becoming a very worrying problem, as it is increasing in the community due to undervaccination of many children. This is a potentially fatal disease, and even if the child survives the distress of weeks or months of severe coughing, they may be left with permanent brain or lung damage.

Haemophilus influenzae B causes a severe form of meningitis, and rarely a throat infection (epiglottitis) that can cause part of the throat to swell so much that the child suffocates. This infection can be prevented by three or four HiB vaccines starting at 2 months of age.

Hepatitis B is a viral infection of the liver, which may cause life long complications. It is spread by blood, bodily fluids and sex. It requires three vaccinations in childhood.

Measles is often considered to be a mild disease, but a small percentage of children even in developed countries develop debilitating ear, chest and brain complications that may affect them for the rest of their lives. The measles vaccine is combined with the mumps and rubella vaccination and is given at 12 months and again at 4 years of age, but it can be given at any age if vaccination has been neglected at the correct age.

Mumps is a relatively benign disease of childhood, but it too may have serious consequences, particularly if it is caught in adult life when it may spread to the testes and cause sterility, or infect the brain and cause permanent damage.

Polio was probably the most feared of childhood diseases. If it didn't kill a child, it probably left them crippled for life. 1956 was the last year before the original Salk injectable vaccine became available, and it was the year of the last polio epidemic in Australia. Parents were so scared for their children, that when the vaccine became available, there were queues down the street from the clinic front doors that rivalled the scene before a modern pop concert. They wanted their children protected, and as soon as possible. The Sabin vaccine is now given by mouth to prevent this disease, but boosters are required into adult life every ten years.

German measles (rubella) vaccination is more important for girls as it can cause severe deformities to the foetus if contracted in pregnancy. To reduce the risk of spreading this disease, the vaccination is given in combination with measles and mumps at 12 months of age, and an additional booster is given at 4 years of age.

All routine childhood immunisations are now given by injection. The oral polio vaccine (Sabin) was used until about 2005 and was given as a few drops that were swallowed. If the child has a high fever or other significant illness, the vaccination may be delayed for a few days until it has recovered.

Significant complications after all childhood vaccinations are rare. A sore arm or leg at the site of the injection is relatively common, and likely to be worse with bruising caused by movement of the child during the injection. Firm restraint by the parent for the 15 seconds that the injection takes can prevent this.

Fever and irritability may occur after a triple antigen, and giving paracetamol before the injection is sensible.

Measles vaccines may cause a very mild case of measles in about 2% of children.

Any other risks are minimal, and certainly far rarer than the serious complications of any of these diseases.

See also CHILDHOOD; TRIPLE ANTIGEN; VACCINES

VACCINES

Vaccines are antigenic substances that are introduced into the body (by injection, tablet or mixture) to induce immunity to a particular disease by causing the production of antibodies against the infecting agent. Vaccines are

often in the form of killed bacteria or viruses and are given by injection, or living organisms that have been altered so that they cannot cause disease (eg. Sabin polio) and are given by mouth.

Vaccines commonly available include those that protect against the following diseases:-

VACCINES AVAILABLE

Side effects vary between different vaccines but are usually confined to local inflammation at the site of the injection, fevers, irritability, and in rare cases, a very mild dose of the disease (eg. measles).

VIRUS

A virus is an infective agent smaller than a bacterium, is not a cell, is unable to be seen using a light microscope, has no internal metabolic processes, and is unable to replicate without the use of a living cell.

Viruses are unimaginably small, and millions could exist on this full stop. They can be found anywhere in the environment - in the body, or in a drop of sweat, in saliva, or the skin of the family dog.

In the body, they will be under constant attack by the body's defence system. Every minute, millions more viruses enter the body through the mouth or nose. As they enter, the defence system uses its special cells and protein particles (antibodies) to repel the attack. Sometimes the defences are overwhelmed for a short time by the rapidly multiplying viruses. When this happens, the patient may feel off-colour for a day or two. If the virus numbers manage to totally defeat the defenders, a full-blown viral infection will develop. Viruses can cause diseases as diverse as measles, hepatitis, cold sores, chickenpox, glandular fever, AIDS and the common cold.

Virus particles are so small that they cannot be seen by even the most powerful light microscope, and special electron microscopes have to be used. They are neither animal nor plant, but particles that are so basic that they are classified into a group of their own. They are not alive in any sense that we understand, but are overgrown molecules that are intent on reproducing themselves at the expense of any host that happens along. Viruses can only exist and multiply inside the cells of the body. Because they are not truly alive, they cannot be killed, and so antibiotics that are effective against the much larger and living bacteria have no effect on viruses. Other than for a limited number of viruses that cause genital herpes, shingles, cold sores and influenza in the first 36 hours of the infection doctors have no cure for virus infections.

Viruses cause diseases as diverse as measles, influenza, hepatitis, cold sores, chickenpox, glandular fever, the common cold, and AIDS. Viruses can actually infect the much larger bacteria, and this ability is used by scientists to introduce new genes into bacteria in genetic engineering.

The common cold can be caused by any one of several hundred different viruses. They cause the lining of the nose, sinuses and throat to become red, sore and swollen; and phlegm and mucus are produced in great quantities to give a stuffy head, sore throat and runny nose to their victim. The poisons created by the body destroying the viruses circulate around in the blood stream to cause the fever and muscular aches that are also associate with a cold. While the patient is suffering, the body is busy producing the appropriate antibodies to fight the infection. Once the number of antibodies produced is adequate to destroy most of the viruses, the symptoms of the disease disappear.

Doctors can vaccinate against some viral diseases, such as measles and influenza, to prevent them; but others such as the common cold cannot be prevented. Viral infections can best be avoided by a good, well-balanced diet, reasonable exercise, avoiding stress, avoiding extremes of temperature, and avoiding those who already have the infection.

See also BACTERIA; COLD, COMMON; CYTOMEGALOVIRUS INFECTION; ROTAVIRUS; TOGAVIRUS; VACCINATION