Shot in the arm

The Star Online > Health

Wednesday January 16, 2008

Shot in the arm

By Dr MILTON LUM

Vaccinations help prevent disease and their benefits far outweigh the risks.
Widespread vaccination has virtually eradicated many infectious diseases in the world.

ALL of us get infected by organisms like bacteria, viruses and parasites. Infants and children are particularly vulnerable. It is relevant to know how the body responds to infections and how medicine has developed ways of dealing with some infectious diseases.

Active immunity

The body responds to infections by producing antibodies, which are proteins that attach themselves to the organisms, marking them for the white blood cells to identify and destroy. As long as there are circulating antibodies, the body is protected from the infective agent. The antibody levels decrease over time and the protection may, in certain diseases, eventually disappear.

Passive immunity

In an acute infection, injecting antibodies made from the blood of humans or animals with immunity to a specific infection can provide immediate protection. Since the body is not making its own antibodies, the protection provided is temporary, as the injected antibodies do not survive for more than a few weeks, such as in the case of hepatitis A.

Another method of achieving passive immunity is to inject human immunoglobulin which is obtained from pooled donated blood containing a collection of antibodies to diseases common in the general population such as measles, mumps, rubella, hepatitis A and chicken pox. The immunoglobulins do not have antigens, which are substances that stimulate the production of an antibody in a carrier of the disease. There are also immunoglobulins made from donors who have had specific diseases, such as hepatitis B and tetanus.

As there are two types of immunity, so there are two types of immunisation, active and passive, with the former always preferable to the latter, since prevention is better than cure. However, passive immunisation may be needed to treat an acute infection. It is often not uncommon that passive and active immunisation are combined, the former providing immediate treatment while the active production of antibodies provides longer term protection. Why immunise

Widespread vaccination has virtually eradicated many infectious diseases in the world. The classical example is small pox, which now only exists in certain laboratories. The incidences of some infectious diseases have decreased considerably with vaccination. Since the World Health Organisation (WHO) launched its Global Polio Eradication Initiative in 1998, infections have decreased by about 99%, saving about five million people from paralysis.

Newer vaccines have been and are being developed and this has contributed to protection against more serious infectious diseases. The hepatitis B vaccine which was introduced about two decades ago helps in the prevention of liver cancer, while the recently introduced human papilloma virus (HPV) vaccine helps in the prevention of HPV infection, a leading causative factor of cervical cancer.

Vaccination provides protection against specific diseases. There may be side effects and risks, which are very much less than that of the disease itself. The benefits of immunisation far outweigh the risks.

Types of vaccines

Vaccines stimulate the production of antibodies without the person having the illness. There are three main types of vaccines:

# Live attenuated vaccine is an extremely weak preparation of a live infectious organism (measles, mumps, rubella)

# Inactivated vaccine is a preparation of a killed infectious organism (typhoid)

# Detoxified exotoxins and extracts of exotoxins are preparations of poisonous substances made by some bacteria that have been made safe for human use by chemical processes (diphtheria, tetanus).

Some vaccines are given as combinations, such as diphtheria-pertussis-tetanus (DPT) and measles-mumps-rubella (MMR).

Immunisation schedule

Immunisation is provided to all babies born in both the public and private sectors. Various countries have slightly different immunisation schedules, depending on the prevalence of the serious infectious diseases and affordability. It is advisable to adhere to the schedule to obtain maximum benefit.

Efforts should be made to ensure the immunisation of children who are at greater risk of infectious diseases, such as children with congenital heart disease and/or mongolism (Down’s syndrome) and those who are born premature, remain small for their age, are HIV positive or have asthma.

When not to immunise

Active immunisation with live vaccines can pose danger to certain individuals, such as those with severe immunodeficiency disorders, those who have had severe reactions to vaccines previously, anyone suffering from any acute illness and anyone on high doses of steroids or immunosuppressive medicines.

An infant who is HIV positive should receive live vaccines for measles, mumps, rubella, and polio and inactivated vaccines for hepatitis B, diphtheria, tetanus, pertussis, polio, cholera and typhoid.

Vaccination can result in severe allergic reaction in those who are very sensitive to one or more of its components. Those with egg allergy should not be given MMR vaccine as it is made in chicken eggs. Some vaccines contain very small amounts of antibiotics, for instance neomycin and polymxin, which can stimulate an allergic reaction in some individuals.

It is advisable for parents of children with food allergies to consult their doctor prior to vaccination. Vaccination should be postponed until an infant has recovered from an acute illness. Vaccination may be given to an infant who has a minor illness, without fever, or with minimal symptoms.

Most vaccines are given by injections into the skin. Some vaccines like polio are given as mouth drops.

Effectiveness and safety

Although there is no vaccine that is 100% safe or effective, all vaccines used in routine immunisation are very effective in preventing disease. It is usual to give more than one dose of a vaccine to increase the likelihood of developing antibodies.

Although vaccination is generally safe, some babies may develop side effects or adverse reactions, which are minor . Some vaccines, such as polio, have very few side effects while others, such as rubella, may produce a very mild form of the disease.

Swelling at the injection site, a low grade fever and rashes are not uncommon. This usually goes away in about 36 hours and is a sign that the baby’s immune system has been stimulated.

Serious complications are very rare. Severe allergic reaction (anaphylaxis) is extremely rare. Its incidence is one in 100,000 with measles vaccine. It is dangerous and may result in damage. It is impossible to predict who may get this unless an allergic reaction had occurred previously.

Media reports have tended to sensationalise the extremely rare, adverse reactions to vaccination. If you have any concerns about any aspect of vaccination, a discussion with your doctor instead of withholding vaccination from your child, is a wiser approach.

When children are not vaccinated, they are very vulnerable to preventable diseases. The children are much more likely to be harmed by the disease than by the vaccine itself.

# Dr Milton Lum is chairperson of the Commonwealth Medical Trust. This article is not intended to replace, dictate or define evaluation by a qualified doctor. The views expressed do not represent that of any organisation he is associated with.

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