Original Antigenic Sin

This is why although vaccines are an incredible tool, vaccination is not always sufficient in the long term, depending on the rate of recombination of the bug and other factors.

Although you gain a highly specific response to whatever was in the vaccine, you may weaken the general response which could later have saved you from a weird microbe that has features that are way different from what was in the vaccine.

Don't tell the antivaxxers though.