Vaccines can be of different types; those against COVID-19 (unlike others that may contain modified forms of a virus or a bacterium) contain a particular substance present in the same virus, the Spike protein, which alone does not cause the disease but has the task of soliciting a immunological response similar to that caused by the infection of the SARS-CoV-2 virus, teaching our immune system to respond, when attacked, in a short time, thanks to a kind of immunological memory.