Immunizations that stimulate the body’s defense system to fight off disease are the best way to protect yourself from serious illness at home and on the road. When traveling, your need for a particular vaccine depends on the countries you are visiting, your age, the season, your length of stay, your lifestyle and overall health.

The Centers for Disease Control and Prevention divides vaccines for travel into three categories: routine, recommended and required. Routine vaccines include those that you ordinarily would — or should — receive from your physician or healthcare provider, such as the tetanus, diphtheria and acellular pertussis (Tdap) vaccine; the measles, mumps and rubella (MMR) vaccine; and flu shots. Adults who received these vaccines as children may require “booster” shots later in life. This depends on the immunization and when you received it. Ask your physician for advice and remember that some immunizations are not recommended for pregnant women or adults with certain medical conditions.

Recommended vaccinations, as defined by CDC, serve two purposes. First, they protect you from illnesses that might be prevalent in the places you visit. Second, they help control the spread of disease by ensuring that you do not bring infectious diseases home with you.

You won’t be turned away at the proverbial door if you arrive on foreign soil without these routine and recommended immunizations, but they’re suggested for your protection. For instance, the diphtheria vaccine is recommended for travel to Russia, the independent countries of the former Soviet Union, and parts of Africa, Asia, Eastern Europe and Central and South America. In addition, every traveler should be vaccinated against tetanus since even a small cut can turn into a big concern if it exposes you to the spores that cause the disease.

Vaccination against polio is recommended for travel to parts of Africa, Asia, the Middle East and much of the former Soviet Union. If you never received a polio vaccination, which is administered as a liquid, the recommended schedule is two doses of vaccine given four to eight weeks apart with a third dose given six to 12 months later. If you were vaccinated against polio in childhood, you can request a single, lifetime booster dose as an adult.

Typhoid vaccine is highly recommended for travelers to India. Malaria vaccine is recommended for travelers to certain tropical and subtropical destinations.

Other recommended vaccines include those for hepatitis A and hepatitis B. The latter is recommended for travelers to Southeast Asia, Africa, the Middle East, some Pacific Islands, Haiti, the Dominican Republic and the Amazon region of South America. Hepatitis B may be contracted by travelers who undergo medical or dental procedures overseas and those who receive injections with needles that are not properly sterilized.

Required vaccinations are the ones that you must have in order to be granted permission to enter certain countries. Most common is the vaccination against yellow fever. Sixteen countries in tropical South America and sub-Saharan Africa, including Cameroon, French Guiana, Ghana, the Ivory Coast and Rwanda, will deny entry to travelers who have not received yellow fever immunization. In addition, a much longer list of countries, including some in Europe and the Caribbean, require yellow fever vaccination if you have traveled from, or through, countries in “endemic zones” — that is, regions where yellow fever is present and actively transmitted. Endemic zones include virtually all of central Africa, including Ethiopia, Kenya and Tanzania, and large sections of South and Central America, including much of Brazil, Colombia, Peru and Venezuela.

When you receive your vaccination, request a signed, stamped International Certificate of Vaccination from the physician or clinic where the vaccine was administered. Carry the certificate with you when you travel; you might be required to present it when you arrive at your international destination. The certificate is valid for 10 years from the date of vaccination.

As mentioned above, some vaccines are strongly recommended or required for travel at particular times of the year. One example is the meningococcal vaccination to guard against the spread of meningitis that is required for travel to Saudi Arabia during the Hajj. (The government of Saudi Arabia may also require travelers from certain countries to present proof of yellow fever immunization for travel during the Hajj.)

Because vaccines take a few days to become effective (and some require a course of doses) you must plan your vaccination schedule well in advance of your travel — ideally, visit your healthcare provider four to six weeks before you depart. Travel web sites such as http://www.cdc.gov/travel and http://www.travelersvaccines.com allow you to search by destination to determine the vaccinations recommended for your travels.