Dear Doctor: Is a COVID-19 vaccine the same as a flu shot? I had a violent reaction to a flu shot in 1976 that continues to have an effect in my body today, and I am 74 years old. I want to get the COVID-19 vaccine, but I fear another severe reaction.
Dear Reader: The vaccine against the coronavirus that causes COVID-19 is not the same as the influenza vaccine. Although each vaccine targets a virus that causes a respiratory illness, they use different mechanisms to prime the body’s immune response.
Let’s start with the flu vaccine. This is what is known as an inactivated vaccine. It contains a portion of the microorganism that causes the disease the vaccine is targeting. However, the word “inactivated” means that this microorganism has been rendered harmless. It cannot cause disease. When injected, the body’s immune system recognizes the inactivated virus as a threat and learns how to mount a defense against it. Then, when the body becomes infected with an actual virus of the same type, it’s already primed to fight it off.
The coronavirus vaccines, by contrast, are a class of vaccines known as mRNA vaccines. Instead of a particle of the virus to teach the immune system what to look out for, they use a single strand of genetic code known as messenger RNA. In the case of the new coronavirus vaccines, it’s a harmless fragment of the spike protein that the coronavirus uses to penetrate a host’s cell. Armed with the molecular code to the spike protein, the body now knows how to recognize and dismantle it. And with its spike proteins disabled, the coronavirus infection is stopped in its tracks.