Vaccination aims to prevent infectious diseases by introducing weakened or inactivated forms of pathogens into the body, allowing the immune system to develop protection without causing illness.

Vaccination induces artificial immunity, which is acquired through the introduction of antigens into the body, either through vaccines or exposure to weakened or inactivated pathogens.

Memory cells play a crucial role in vaccination by recognizing and responding to specific pathogens quickly upon re-exposure, providing long-term protection against infection.

Live attenuated vaccines contain weakened or attenuated pathogens that are still capable of replication, but they are unable to cause disease. Examples include measles, mumps, and rubella (MMR) vaccine and the oral polio vaccine (OPV).

Inactivated vaccines contain pathogens that have been killed or chemically inactivated. They stimulate the production of antibodies against toxins produced by the pathogens, providing protection against diseases caused by bacterial toxins.

Toxoid vaccines contain inactivated toxins produced by bacteria. They stimulate the production of antibodies against these toxins, providing protection against diseases caused by bacterial toxins, such as tetanus and diphtheria.

Subunit vaccines contain only specific antigens or components of the pathogen, rather than the whole organism. This makes them safer and less likely to cause side effects compared to whole-cell vaccines.

The recommended vaccination schedule for children in the United States includes MMR, polio, and DTaP vaccines at birth, hepatitis B vaccine at 1 month, Hib vaccine at 2 months, and varicella vaccine at 12 months, among others.

MMR vaccine is recommended for pregnant women to prevent congenital rubella syndrome, a serious condition that can cause birth defects if a pregnant woman contracts rubella during pregnancy.

Herd immunity is achieved when a large proportion of a population is vaccinated, making it less likely for an unvaccinated individual to come into contact with an infected person and become infected. This reduces the spread of infectious diseases and protects vulnerable individuals who cannot be vaccinated.

Yellow fever vaccine is recommended for travelers to prevent yellow fever, a mosquito-borne viral infection that can cause severe illness and death. It is required for entry into certain countries where yellow fever is endemic.

The recommended vaccination schedule for adults in the United States includes Tdap vaccine every 10 years, influenza vaccine annually, pneumococcal vaccine at age 65, and zoster vaccine at age 50, among others.

Hepatitis B vaccine is recommended for healthcare workers to prevent hepatitis B, a viral infection that can cause liver damage and liver cancer. It is transmitted through contact with infected blood or bodily fluids.

Vaccination can reduce the incidence of disease to very low levels, potentially leading to the eradication of certain diseases. Examples include smallpox, which was eradicated through a global vaccination campaign.

Typhoid vaccine is recommended for travelers to prevent typhoid fever, a bacterial infection that can cause fever, abdominal pain, and diarrhea. It is transmitted through contaminated food or water.