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In 7-9 by Rockstar (4.8k)  
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by Rockstar (4.8k)  
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What is a virus?

- Viruses are structures made of proteins that need the genetic machineries of life forms to reproduce. Whether viruses are considered alive or not is still under debate.

- Specific viruses usually infect specific host species, and cross-species infections are rare. For example, viruses infecting plants cannot infect animals. Viruses infecting specific animals usually do not infect other animals (although it can happen, like with the HIV or the COVID).

- Viruses are often harmless to their host organism, but they can be at the origin of pathologies if they disrupt the functioning of their host organism.

- Detrimental infection by viruses are fight by the host organism through their immune system.

Immune system and pathogens

- Pathogens are agents, such as viruses or bacteria, that are disrupting the functions of an organism.

- Affection by a pathogen is at the origin of many diseases, but the immune system is what allows the organism to eliminate the pathogens.

- When affected by viruses, the immune system usually "remembers" how to fight future infections by the same virus: it is what provides immunity.

Vaccines and immunity

- Immunity is what allows the immune system of an organism to fight a pathogen before it does damages to the organism.

- Vaccines are using this system to create an immunity to a disease without having to suffer a pathology. 

- By mimicking a virus, vaccines create an immune response and induce an immunity without having to suffer the actual disease.

- It is extremely effective to reduce the occurrence of many viruses like cholera, hepatitis B, measles, polio, rabies, tetanus, typhoid... 

- One of the most impressive achievement of vaccines is the eradication of the smallpox, a virus which had a 30% mortality rate and has been officially eradicated in 1980.



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