How the Flu Shot Protects You From Getting Sick—Yale Medicine Explains

Have you ever wondered about what vaccines—such as flu shots—are doing in your body once you’ve received them?  

According to Onyema Ogbuagu, MBBCh, a Yale Medicine infectious diseases specialist, the main event after vaccination is an immune response that, it is hoped, “protects you when you see the real virus.”  

For some, that immune response can lead to symptoms that mimic the illness itself. These flu-like symptoms can include fatigue, muscle aches, and sometimes even fever. But even though these symptoms are unpleasant to experience, Dr. Ogbuagu emphasizes that they are actually a positive sign that the shot is working, indicating that your body has mounted an immune response that should protect you if you are exposed to the illness. No vaccine is 100% effective, so there will always be “breakthrough” cases. But even when vaccination doesn’t stop the illness, its symptoms will be less severe. Those who get the flu after receiving a flu shot will have a milder case than those who didn’t get the vaccine.  

But if the vaccines are sitting unused, the shots do no good whatsoever.    

“Vaccines don’t save lives, but vaccination does,” Dr. Ogbuagu says. “We can always have effective vaccines, but if people don’t take them, then we don’t achieve the protection that we all desire.”  

In this video, Dr. Ogbuagu explains how flu vaccines work—and why they’re important.