Made up of millions of individual white blood cells, the immune system patrols the body in search of germs. When tissues are under threat, it mounts a two-pronged attack. First, the innate immune system gets to work to slow germ growth and prevent spread. Then the adaptive immune system comes in to eliminate the threat.
The adaptive immune system has powerful weaponry, but it takes a while to deploy. This is because the cells of the adaptive immune system can each only attack one type of infection. When the body encounters a new germ, it needs to find the right cells and prepare them for battle. This process can take up to one week, and in that time people can sometimes become very unwell.
This is where vaccines come in. Rather than wait to encounter a dangerous disease like measles in the world , a vaccine gives the immune system a chance to prepare in advance. Vaccines contain weakened or dead germs, or parts of germs, along with something called an adjuvant. This helps to alert the immune system to danger, encouraging it to start mounting an attack. With access to parts of the germ, the immune system can find the right cells and get them ready.
Many of the cells made during a vaccination disappear afterwards, but some stick around as ‘memory cells’. They stay in the bloodstream for decades, constantly on the lookout for their matching germ. If the infection then happens for real, these memory cells spring into action straight away. They divide to produce an army of clones that appears in a matter of hours instead of days. This can clear the infection before it takes hold, preventing us from getting sick at all.