Vaccines contain around 25 micrograms of mercury per 0.5 mL dose.
The mercury contained in vaccines is in a healthy amount and will do no harm to you and there's no way of getting mercury poisoning or other health issues from vaccines.
You should get a vaccine when you need to because the vaccine will help protect you against other health issues and the benefits of the vaccine outweighs the risk.
The mercury that vaccines contain is required because the mercury is actually a preservative for the vaccine to extend the shelf life.
If the vaccines didn't contain the mercury it would go bad quicker.