How do the vaccines work?

Poster for video

mRNA vaccines and immunity

Melanie Swift, M.D., COVID-19 Vaccine Allocation and Distribution, Mayo Clinic: We've got two really effective vaccines from Pfizer and Moderna. These vaccines are about 95% effective at preventing COVID-19 disease.

These vaccines work by delivering some of this mRNA into our cells. The SARS COV-2 virus got a genetic code of its own. There is a little segment, a tiny little snippet of that, that actually codes for the spike protein. The spike protein is the thing that helps this virus get into our cells and infect us.

mRNA is like a little recipe for how to make that spike protein. When we get these vaccines, our body makes that spike protein and we develop an immune defense to it without ever having to be exposed to the whole virus. It's not exposing us to the whole virus at all, live or killed. It's only allowing us to make a little bit of that spike protein, which is just a tiny portion of the virus, and then we react to that and become protected from the whole virus.

mRNA in these vaccines can only get into the main part of the cell, but it can't get into the nucleus of the cell, which is where our own DNA lives. It can't incorporate into our DNA. It also doesn't live very long, and it doesn't last very long. It's very fragile, and that's why it has to be stored at these ultra cold temperatures. It's not stable for very long. So, it goes into the body, it goes into the cell for a matter of hours, and starts to make this protein. Then in the coming days, our bodies react to that protein but that messenger RNA doesn't hang around nor does it get into our DNA.

Key takeaways


COVID-19 vaccines cause the immune system to make antibodies to fight the COVID-19 virus.

The Food and Drug Administration (FDA) has given emergency use authorization to two types of COVID-19 vaccines and approval to one vaccine. Coronaviruses have a spikelike structure on their surface called an S protein. Messenger RNA (mRNA) vaccines give your cells instructions to build a harmless piece of an S protein. Viral vector vaccines place genetic material from the COVID-19 virus into a modified version of a different virus. When this different virus enters your cells, it delivers genetic material from the COVID-19 virus that gives your cells instructions to make copies of the S protein. Both vaccines then cause the immune system to make antibodies to fight the COVID-19 virus.

More about how the COVID-19 vaccines work