Depending on the target, vaccines can allow the immune system to eliminate it before it can start multiplying significantly. For things like measles etc, this effect is strong enough to provide effective immunity. Whether vaccines can stop infections depends a lot on how you define infection. They won’t magically stop the virus being able to enter your body. They can stop them from establishing themselves and stop you becoming infectious to others.
Unfortunately, the coronavirus family viruses are particularly slippery. Even our primary immunity from infection is often short lived. COVID is ridiculously good at both hiding from the immune system, and spreading to new hosts. The vaccine provides significant protection, but isn’t effective enough to provide complete immunity.
Vaccines aren’t designed to stop infection. They never intended to.
The vaccine is intended to get your body familiar with the virus so that when you do get it your body knows exactly how to fight it.
Depending on the target, vaccines can allow the immune system to eliminate it before it can start multiplying significantly. For things like measles etc, this effect is strong enough to provide effective immunity. Whether vaccines can stop infections depends a lot on how you define infection. They won’t magically stop the virus being able to enter your body. They can stop them from establishing themselves and stop you becoming infectious to others.
Unfortunately, the coronavirus family viruses are particularly slippery. Even our primary immunity from infection is often short lived. COVID is ridiculously good at both hiding from the immune system, and spreading to new hosts. The vaccine provides significant protection, but isn’t effective enough to provide complete immunity.