Am I immune to measles?
You are most likely immune if:
you were born in US before 1957 who
had measles disease
2 doses of measles vaccine
Blood test proved measles IgG (immunity)
If you were born in 1960s-1980s before 2 dose measles vaccine recommendation in 1989, only way to be sure you are immune is to check immunity or get a booster MMR vaccine.
In Japan 2 dose measles vaccine recommendation started in 2006. If you were born and raised in Japan and now in your 50s or older, you probably had measles disease as a child.