Messenger RNA vaccines are a new type of vaccine that works different than the other types of vaccines that we are used to getting. Normally, vaccines are made by injecting a ‘deactivated’, harmless portion of the virus itself into the body to allow the body’s immune system to recognize the structure of the virus or of it’s associated proteins, without the risk of a harmful infection. The body identifies the foreign body and creates antibodies specific to it. These antibodies are what makes us immune to any disease. When the person catches the actual virus, the body is ready to fight off the infection with the antibodies that it made from the vaccine.
Messenger RNA vaccines work in a different manner. In this type of vaccine, we inject modified messenger RNA, that contains a sequence of bases that would be able to teach the cells of our body to make portions of viral proteins, into the muscles cells of our body. Normally mRNA in our body functions by taking instructions from the DNA, in bits and pieces and carries that information to the protein synthesis pathway for the synthesis of proteins. With the vaccine mRNA in the muscle cells, the protein synthesis pathway now starts making viral proteins but due to modified nature of the vaccine mRNA, the protein made is harmless.
The body recognizes the protein being made as foreign and starts creating antibodies against that protein structure, which is similar to the actual viral protein structure and effectively makes us immune to the virus itself.
Some of the COVID-19 vaccines, including Pfizer vaccine, uses this mechanism of action. These vaccines have been rigorously tested and have been held to high standards before allowing emergency use in the United States and other countries. MRNA vaccines do not use the live virus and therefore you cannot get infected with the vaccine.