Infectious disease and vaccines

This page is reference information compiled from the cited sources. It is not medical advice. For any decision about health, diagnosis or care, consult a qualified professional.

What it is

A vaccine is a biological preparation that provides active acquired immunity to a particular infectious or malignant disease. It typically contains an agent that resembles a disease-causing microorganism, often made from weakened or killed forms of the microbe, its toxins, or one of its surface proteins. The agent stimulates the immune system to recognize the agent as a threat, destroy it, and recognize and destroy any of the microorganisms associated with that agent in the future. Vaccines can be prophylactic to prevent or alleviate the effects of a future infection, or therapeutic to fight a disease that has already occurred. The administration of vaccines is called vaccination.

Key facts

The safety and effectiveness of vaccines has been widely studied and verified. Vaccination is the most effective method of preventing infectious diseases, and widespread immunity due to vaccination is largely responsible for the worldwide eradication of smallpox and the restriction of diseases such as polio, measles, and tetanus. The World Health Organization reports that licensed vaccines are available for twenty-five different preventable infections. Some vaccines offer full sterilizing immunity, in which infection is prevented. Vaccines also help prevent the development of antibiotic resistance, for example by reducing the incidence of pneumonia caused by Streptococcus pneumoniae and thus reducing the prevalence of antibiotic-resistant infections. There is overwhelming scientific consensus that vaccines are a very safe and effective way to fight and eradicate infectious diseases. The measles vaccine is estimated to prevent a million deaths every year. As long as the vast majority of people are vaccinated, it is much more difficult for an outbreak to occur or spread, an effect called herd immunity. Limitations to effectiveness exist, and protection can fail for vaccine-related reasons like failures in attenuation or administration, or for host-related reasons if the immune system does not respond adequately. In some cases, vaccines may result in partial or temporary immune protection rather than full or permanent immunity, but they can still mitigate the severity of infection.

When to seek professional help

Host-related determinants can be factors affecting the severity of infection and response to a vaccine. These determinants include genetics, health status such as underlying disease, nutrition, pregnancy, sensitivities or allergies, immune competence, and age. Individuals may be allergic to ingredients in the vaccine. The host's immune system may not respond adequately or at all for host-related reasons, which occurs in an estimated 2–10% of individuals. Factors for this lack of response include genetics, immune status, age, health and nutritional status. One type of primary immunodeficiency disorder resulting in genetic failure is X-linked agammaglobulinemia. Those who are older often display less of a response than those who are younger, a pattern known as immunosenescence.

Source: Vaccine (CC BY-SA 4.0 (Wikipedia)), retrieved 2026-09-19.