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Vaccination works in two ways. One, every person who receive vaccines become immune to the disease they are vaccinated against. Two, vaccinations protect the society through herd immunity. The immunity developed from vaccinations provides protection for that individual against the disease, while herd immunity prevents infectious diseases from spreading in society.
Immunity for those vaccinated
Vaccination provides the vaccinated person with protection against getting sick when they later encounter an infection. For some vaccines, one dose is sufficient for protection. While for other vaccines, several doses are required. Sometimes you need to get booster doses, for long-term protection.
The immune system creates immunity, that is, the protection against getting sick from the infection.
When a person cannot become sick from an infection, then that person cannot spread the infection to others. So, when you vaccinate large parts of a population, the infection cannot spread. This herd immunity becomes a very important part of vaccination protection.
If a mother was vaccinated, they provide some vaccination protection to the newborn baby. But that protection disappears during the first few months of life. Therefore, infants will always be susceptible to infections before they have had time to receive their vaccination protection. In a well-vaccinated population, we protect infants through herd immunity.
Live vaccines (eg. measles and chickenpox vaccines) cannot be given to people with very severely compromised immune systems. Their immune system can be very severely compromised through cancer treatment or treatment for certain autoimmune diseases. Some people are born with severe immunodeficiency. These people will not only be unprotected against measles, but exposure to the disease will put them at high risk of becoming extra ill . Herd immunity protects them.
Eradicating a disease
Herd immunity makes it possible to eradicate certain infectious viral diseases. Viruses cannot live by themselves, they must always live in a host. So if you vaccinate large populations, then most people will be immune to the virus, and therefore the virus will not be able to find a host to live in. Thus you eradicate the disease. This is applicable to diseases where humans are the only host. Smallpox became extinct by worldwide vaccination.
Polio is close to extinction, but as terror groups have prevented vaccination in some areas of North Africa, the disease continues there. A few decades ago, there was hope of eradicating measles. Unfortunately though, we have seen many major outbreaks in both Europe and the United States in recent years. These outbreaks usually start from countries where there has been poor vaccination protection or groups of people who have been opposed to vaccination and thus opted out of it. In these groups there is no herd immunity and therefore the disease can spread.
Everyone must have their own protection against Tetanus
Tetanus is a deadly and painful bacterial disease in which the bacteria live in soil. There is no herd immunity. Therefore everyone must be given their own protection against tetanus. Children receive protection against tetanus with the three-month vaccine in accordance to the Swedish National Immunization Program.
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