The vaccine made by dead cells of virus or bacteria is called killed vaccine. For example, vaccination against influenza, cholera, polio, rabies, hepatitis etc.

The vaccine prepared by inactivating live bacteria is called live vaccine. For example, vaccination against measles, mumps, rubella, chicken pox, typhoid etc.

Vaccines are divided into five categories. These are-

1. Live vaccine: The vaccine prepared by inactivating live bacteria is called live vaccine. For example, vaccination against measles, mumps, rubella, chicken pox, typhoid etc.
2. Killed vaccine: The vaccine made by dead cells of virus or bacteria is called killed vaccine. For example, vaccination against influenza, cholera, polio, rabies, hepatitis etc.
3. Toxoid vaccine: Toxoid vaccine is made by inactivating the toxic substances of bacteria with formaldehyde. For example, vaccination against diphtheria, tetanus, etc.
4. Sub unit vaccine: This vaccine is made from a small part of the germ cell (protein). E.g. Hepatitis B, Papilloma Virus Vaccination.
5. Conjugate vaccine: The vaccine made by two different components of the virus is called Conjugate vaccine. E.g. Haemophilus vaccine.

A suspension of live, half-dead or dead bacteria capable of inducing antibodies is called a vaccine. It does not cause any disease in the body. However, it prevents disease.

The process by which antibodies stimulate the process of phagocytosis is called opsonization. In this process, hundred times more germs are destroyed in less time.

Strong antibodies attack the germ coat. It destroys the germ layer. As a result, germs are eliminated.

The process in which the harmful effects of microbes are neutralized is called neutralization. Antibodies cover the toxin site of the bacterium. In this the bacteria cannot apply antigens to the host body. As a result, there is less chance of damage.

The precipitation of substances due to the action of antibodies and antigens is called precipitation. Reaction occurs between antibody and antigen. The reactants are precipitated. As a result, the germs die.

The process by which the antibody reacts with the antigen and clumps the bacteria together is called agglutination. Each antibody has two antigen binding sites. So each antibody blocks two antigens. It then binds and engulfs the antigen.

The function of antibodies in the immune system is specific. That is, a specific antibody acts against a specific antigen or pathogen. The mechanism of action of antibodies in the human body is discussed below.

1. Agglutination: The process by which the antibody reacts with the antigen and clumps the bacteria together is called agglutination. Each antibody has two antigen binding sites. So each antibody blocks two antigens. It then binds and engulfs the antigen.
2. Precipitation: The precipitation of substances due to the action of antibodies and antigens is called precipitation. Reaction occurs between antibody and antigen. The reactants are precipitated. As a result, the germs die.
3. Neutralization: The process in which the harmful effects of microbes are neutralized is called neutralization. Antibodies cover the toxin site of the bacterium. In this the bacteria cannot apply antigens to the host body. As a result, there is less chance of damage.
4. Lysis: Strong antibodies attack the germ coat. It destroys the germ layer. As a result, germs are eliminated.
5. Opsonization: The process by which antibodies stimulate the process of phagocytosis is called opsonization. In this process, hundred times more germs are destroyed in less time.