Different countries have different diseases that are prevalent. This is an important thing to keep in mind if you travel, especially to a country like Mexico where getting healthcare may be more difficult if you do become ill. Many of the vaccinations that are recommended before visiting Mexico — such as measles, hepatitis, and polio — are vaccines that already routinely given in the U.S. and that you've probably already had. However, there are a few other vaccines that are not as common in the U.S. and that you should look into getting before you visit Mexico.
Typhoid is a bacterial disease that causes fever, weakness, stomach pain, and diarrhea. It can be spread through contaminated food and water and is quite common in Mexico. Even foods you might assume would be safe, such as salads, could be contaminated with the bacteria that cause typhoid. It is, therefore, a good idea to be vaccinated before you visit. The vaccine is not 100% effective, so you will still want to practice safe food handling and stick to bottled water, but at least you will have an extra layer of protection. The typhoid vaccine lasts about five years, and it's not even a shot; it's a pill you swallow.
The U.S. has a very effective rabies control program; pets are vaccinated, and local health departments provide shots if someone is bitten by a potentially rabid animal. However, rabies is more common in Mexico where not all pets are vaccinated and where people are more likely to come into contact with wildlife. It's a good idea to be vaccinated before you leave, especially if you plan on spending part of your vacation outdoors where rabid animals might be around. Rabies is 100% fatal once you start showing symptoms, so don't skip this one!
Hepatitis A is an infectious disease of the liver. It causes jaundice, weakness, and digestive symptoms. The symptoms typically appear a few weeks after you are exposed, so it can take a while to figure out what is going on. Hepatitis A is spread through food and water, and it is relatively common in Mexico. Therefore, your best bet is to get a vaccine, which will protect you for decades.
Each of these vaccines is quite important if you plan on visiting Mexico. You should aim to get them at least a few months before your visit so you have time to build immunity. Talk to your doctor to learn more about immunizations.