The Pfizer and Moderna vaccines are messenger RNA vaccines, also known as mRNA vaccines. These are a new type of vaccine to protect against infectious diseases, but they have been known and researched for decades. To trigger an immune response, many vaccines put a weakened or inactivated germ into our bodies. Not mRNA vaccines. Instead, they teach our cells how to make a protein from the virus—or even just a piece of that protein—that triggers an immune response inside our bodies. That immune response, which produces antibodies, is what protects us from getting infected if the real virus enters our bodies later.
The Novavax vaccine is a protein subunit vaccine. Instead of mRNA, the vaccine includes proteins from the virus (not the full germ). Once vaccinated, our immune system learns to recognize that the protein should not be there and builds the antibodies that will remember how to fight the virus if we are infected in the future.
The Janssen (Johnson & Johnson) vaccine is similar to mRNA vaccines. They all use a piece of the virus’ genetic code for a piece of the virus’ outer shell. After getting vaccinated, the muscle cells make that piece of the virus, then our immune systems react to that and remember it for the future if we get exposed, killing the invading virus and stopping the infection. With the Janssen vaccine, however, that piece of the virus’ genetic code is inserted into an adenovirus (think common cold) that has been modified so that it cannot replicate and cannot make you sick. Our cells open up the adenovirus, make the piece of the virus’ outer shell, and the process continues as described above.