Get a flu shot from your doctor. This is especially important if you plan to visit Japan between November and April, when the flu bug is most commonly circulating.
Ensure that you get two doses of the vaccination for measles, mumps and rubella, if you've never been immunized against those diseases. This is only necessary for travelers whose birth year is 1956 or later. Get a blood test to check for immunity if you're unsure whether or not you need to seek this protection.
Protect against tetanus and diptheria by getting the appropriate vaccinations from your family doctor. Make sure that your tetanus and diptheria shots are up to date. Doctors say you should get revaccinated at least once every 10 years.
Guard against Japanese encephalitis if you're planning to stay in Japan for longer than a month and will be frequenting rural areas. This is recommended if you will be in Japan between June and September. If you're going to the Ryuku Islands, the risk period for encephalitis runs from April through October.
Don't worry so much about the avian influenza. Despite the paranoia surrounding the bird flu, it is not common in Japan and travelers generally do not need to be concerned about contracting it. Only people who come in direct contact with live or dead infected birds are at elevated risk of contracting it.
Protect yourself against rarer forms of infectious diseases, if you want to be really thorough about your immunizations. Hepatitis E, leptospirosis, lung and Oriental liver fluke, tularemia and scrub typhus are among the other infections travelers may want to be wary of contracting.
