Prevention of infection

Vaccines can protect both the people who receive them and those with whom they come in contact. Vaccines are responsible for the control of many infectious diseases that were once common around the world, including polio, measles, diphtheria, pertussis (whooping cough), rubella (German measles), mumps, tetanus, and Haemophilus influenzae type b (Hib). Vaccine eradicated smallpox, one of the most devastating diseases in history. Over the years vaccines have prevented countless cases of infectious diseases and saved literally millions of lives.
Vaccine-preventable diseases have a costly impact, resulting in doctor’s visits, hospitalisations, and premature deaths. Sick children can also cause parents to lose time from work.

Uses of vaccines
Vaccines contain the same antigens or parts of antigens that cause diseases, but the antigens in vaccines are either killed or greatly weakened. Vaccine antigens are not strong enough to cause disease but they are strong enough to make the immune system produce antibodies against them. Memory cells prevent re-infection when they encounter that disease again in the future. Through vaccination, children develop immunity without suffering from the actual diseases that vaccines prevent.

Most people use the terms ‘vaccination’ and ‘immunisation’ interchangeably but their meanings are not exactly the same.

• Vaccination means having a vaccine – that is actually getting the injection.
• Immunisation means both receiving a vaccine and becoming immune to a disease, as a result of being vaccinated.
The immune system recognises germs that enter the body as “foreign” invaders, or antigens, and produces protein substances called antibodies to fight them. A normal, healthy immune system can produce millions of these antibodies to defend against thousands of attacks every day, doing it so naturally that people are not even aware it is happening. Antibodies often disappear once they have destroyed the invading antigens, but the cells involved in antibody production remain and become “memory cells.” Memory cells remember the original antigen and then defend against it if the same antigen attempts to re-infect a person, even after many decades. This protection is called immunity.

Immunisation enables the body to better defend itself against diseases caused by certain bacteria or viruses. Immunisation may occur on its own (when people are exposed to bacteria or viruses), or doctors may provide it. When people are immunised against a disease, they do not get the disease or get only a mild form of it.

There are two types of immunisation: active and passive.
In active immunisation, vaccines are used to stimulate the body’s natural defense mechanisms.

Vaccines are preparations that contain one of the following:
Non-infectious fragments of bacteria or viruses
A usually harmful substance (toxin) that is produced by a bacteria but has been modified to be harmless—called a toxoid
Weakened (attenuated), live whole organisms that do not cause infection

The body’s immune system responds to a vaccine by producing substances (such as antibodies and white blood cells) that recognize and attack the specific bacteria or virus contained in the vaccine. Then whenever the person is exposed to the specific bacteria or virus, the body automatically produces these antibodies and other substances. The process of giving a vaccine is called vaccination, although many doctors use the more general term immunisation.

In passive immunisation, antibodies against a specific infectious organism are given directly to a person.

These antibodies are obtained from several sources:
The blood (serum) of animals (usually horses) that have been exposed to a particular organism or toxin and have developed immunity
Blood collected from a large group of people—called pooled human immune globulin
People known to have antibodies to a particular disease (that is, people who have been immunised or who are recovering from the disease)—called hyperimmune globulin—because these people have higher levels of antibodies in their blood
Antibody-producing cells (usually taken from mice) grown in a laboratory

Passive immunisation is used for people whose immune system does not respond adequately to an infection or for people who acquire an infection before they can be vaccinated (for example, after exposure to the rabies virus). Passive immunisation can also be used to prevent disease when people are likely to be exposed and do not have time to get or complete a vaccination series. For example, a solution containing gamma globulin (a common type of antibody) is used to help prevent hepatitis in people who travel to certain parts of the world. Passive immunisation lasts for only a few days or weeks, until the body eliminates the injected antibodies.

Vaccines and antibodies are usually given by injection into a muscle (intramuscularly) or under the skin (subcutaneously). Antibodies are sometimes injected into a vein (intravenously).
Vaccines available today are highly reliable, and most people tolerate them well. They rarely have side effects, but they do not work in everyone.

Some vaccines are given routinely—for example, the tetanus toxoid is given to adults, preferably every 10 years. Some vaccines are routinely given to children.

Other vaccines are usually given mainly to specific groups of people. For example, the yellow fever vaccine is given only to people travelling to certain parts of Africa and South America. Still other vaccines are given after possible exposure to a specific disease. For example, the rabies vaccine may be given to a person who has been bitten by a dog.

The Expanded Programme on Immunization (EPI) was established in 1974 through a World Health Assembly resolution (resolution WHA27.57) to build on the success of the global smallpox eradication programme, and to ensure that all children in all countries benefited from life-saving vaccines. This has been adopted by the South African National Department of Health and forms the national protocol for immunisation of children.
The aim of the Expanded Programme on Immunisation in South Africa (EPI-SA) is to prevent death and reduce suffering from vaccine-preventable diseases by immunisation of children.

Immunisation against infections like measles, polio, diphtheria, whooping cough (pertussis), tetanus, hepatitis B, haemophilus influenza type b, rotavirus diarrhoea, pneumococcal diseases and tuberculosis, remains the most cost effective health intervention currently available. These vaccines are provided at no cost


Extract from www.nicd.az.za