Written By: Hanan Khalaf. RPH.

What is immunization?

Immunization is the process of introducing a killed or weakened form of an infectious germ or a derivative of it (vaccine), into the body for the purpose of triggering an immune response. Creating such an immune response means that the body will destroy the invading organism each time it attacks. Immunization process is usually carried out by injection through the skin except for oral polio.

Immunization plays a tremendous role in reducing morbidity and mortality from various infectious diseases, particularly for children below the age of 5 years.

What is the difference between natural immunity and acquired immunity?

The main difference lies in the way of acquiring the immunity. So with natural immunity, the body becomes immune by being exposed to the invading germ, while with acquired immunity it becomes immune by getting the vaccine. The end result is almost the same on the immune system, which in both cases it will attack the invading germ and produce antibodies that are responsible for fighting the germ each time it attacks the body in the future. It can also produce more antibodies if needed. However, getting immune through acquiring the disease, carries a considerable risk of morbidity depending on the type of the disease.

Do vaccines provide 100% protection against the diseases they are used for?

Most vaccines are effective for 85-95% of persons receiving them. They do not provide 100% immunity. However, some of people who are vaccinated might indeed catch the disease, but they tend to have less serious symptoms compared to non-immunized individuals.

Why are some vaccines given as single shots others as several shots?

Several doses of the same vaccine are often needed to achieve full immunity, depending on the type of the vaccine, since some people do not achieve full immunity except with the last dose.

How long does immunity last after getting vaccinated?

Some vaccines do not provide life-long immunity since immunity tend to decrease by time and a booster shot is often needed to cover the problem like tetanus. Others, however, can provide life long immunity like hepatitis B and measles.

What are different types of vaccines?
There are 4 types of vaccines commonly used nowadays:

Live Attenuated vaccines: these contain live viruses but weakened. They usually result in a strong immune response which makes one dose, sometimes, enough to provide life long immunity examples are measles, mumps, varicella (chickenpox).Inactivated vaccines: Such vaccines involve killed (inactivated) bacteria or viruses.Example is polio vaccine.Toxoid vaccine: Involve the use of bacterial toxins, after rendering them inactive, to stimulate the immune system against them. These toxins are produced by bacteria when they invade the body as with Diphtheria and Tetanus.Acellular and subunit vaccines: Involve the use of only part of the virus of bacteria to stimulate the immunity example hepatitis B and Haemophilus influenzae type b.

What types of reactions are to be expected after vaccinations?

Vaccination results mostly in no or only minor local reactions in the form of: Redness and swelling at the injection site, fever, rash. In rare occasions, however, it can trigger seizures, or other types of severe reactions like severe allergic reactions.

At what age should we start with vaccination?

Vaccination usually starts at birth or by 2 months of age, based on current vaccination schedule, and ends by the age of 6 years. However, it is not limited to childhood, adolescents and adults have their own recommended vaccination schedules. It is very important to keep a record of the vaccination history.

Is there any reason why vaccination should not be given to any person?

Vaccination should not be carried on during an acute febrile illness, and should be postponed afterwards. In addition, some vaccines should not be given to persons who suffer from severe allergic reaction to eggs as with measles (egg is used during the process of preparation of measles vaccine) and such cases should be dealt with individually. Moreover, persons with severely disturbed immunity like those immune-deficiency diseases should not receive vaccines that contain live attenuated viruses.

Can vaccination be carried out during pregnancy or lactation?

The general rule is to avoid the vaccination during pregnancy and lactation. Exceptions should be evaluated by the physician on individual basis weighing the risk to the baby versus benefit to the mother and baby as well.

What about the link between some vaccines and occurrence of autism and social and cognitive disorders?

Numerous studies have been conducted but fail to confirm a link between some vaccines as MMR and autism or other social and cognitive disorders. Despite this, numerous parents are still refusing to vaccinate their children. Its good to remember that FDA in association with CDC and National Institute of Health are working continuously to research and monitor vaccine safety and effectiveness

July 1st, 2006

References:

Center of Disease Control
Kids Health

National Library of Medicine

Vaccine InformationWorld Health Organization