If you get any of the COVID-19 vaccines now approved for emergency use in the United States, you may have side effects (and more after the second dose of Pfizer-BioNTech or Moderna shots as opposed to the first). Symptoms, which are generally short-lived and last for a day or two, may include headache, fatigue, injection site reactions, fever and muscle aches and pains. However, they are by no means contagious.

Sabrina Assoumou, MD, MPH, an infectious disease physician at Boston Medical Center and an assistant professor at Boston University’s School of Medicine, explained that the side effects are a result of your body’s normal immune response and there is no living part of COVID-19- virus in the vaccines.

“When I was vaccinated for about 24 hours or 36 hours, I had pain in my arm, the injection site where I was vaccinated. I felt really tired. And after my second shot, I not only felt tired and in pain, but I also had a little fever, “Dr. Assoumou told POPSUGAR.” The reason I got these symptoms was that my body was busy making all these antibodies. “That’s what the immune system does when it recognizes something foreign. in the body (although you should know that if you have zero side effects from the vaccine, it does not mean that you are not building an immune response).

Antonio Crespo, MD, an expert in infectious diseases at Orlando Health, further explained to POPSUGAR that both types of vaccines available in the United States right now tell your body how to create harmless copies of the spike protein found on the surface. of SARS-COV 2 virus, which initiates the production of antibodies; the only difference is how this information is transported into your cells.

The MRNA vaccines from Pfizer and Moderna teach immune cells how to get SARS-COV-2 virus to spike protein through instructions provided in “small lipid beads”, explained Dr. Crespo. Once the protein is made, the cells break down the instructions and dispose of them. The single-shot Johnson & Johnson vaccine uses a special type of virus, adenovirus type 26 (Ad26), as a vector to deliver a piece of the DNA that makes the spike protein. Ad26, according to the FDA, can cause pink eye or cold, but it has been modified for the vaccine and can not cause disease.

“The vaccine does not have a version of the virus that you can spread,” said Dr. Assoumou. So you do not have to worry about “getting” a virus from someone in your household who has symptoms after the vaccine or vice versa. However, it is important to note that it is still possible to get COVID-19 between doses of the mRNA vaccines – and the CDC only classifies someone as fully vaccinated two weeks after the second mRNA vaccine or Johnson & Johnson dose.

POPSUGAR aims to provide you with the most accurate and up-to-date information on coronavirus, but details and recommendations regarding this pandemic may have changed since its publication. For the latest information on COVID-19, please see resources from WHO, CDC and local public health departments.