Skip navigation

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

URL of this page: //


What's this?Play health video with audio description: //



Vaccines help to give the body immunity from infections. Different vaccines work in different ways. Some vaccines inject fragments of a virus or bacteria called antigens into the body. Once in the blood, these antigens circulate among the blood cells, which include red blood cells and white blood cells. White blood cells, such as B and T cells, help fend off foreign invaders.

When antigens invade tissue, they attract macrophages. These are scavenger cells that engulf the antigens. The macrophages then signal to T-cells that the antigens are invading. Killer T cells gather and attack the antigens. Then suppressor T cells stop the attack.

After the vaccination, B-cells make defensive antibodies against the antigen. These antibodies help the cells remember this particular antigen, so that they can fight it off if the body is infected again.

Review Date 7/3/2022

Updated by: Neil K. Kaneshiro, MD, MHA, Clinical Professor of Pediatrics, University of Washington School of Medicine, Seattle, WA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

Related MedlinePlus Health Topics