At least for the flu vaccine. 2009-10 Influenza Prevention & Control Recommendations
Dosage, Administration, and Storage
Looking to see if that's true for others vaccines.
Huh! Hep A dosage varies, too.
"What is the dosage regimen?
Recommended dosages and schedules vary with the patient's age and which specific vaccine is used. Whether you are a child over 1 or an adult, more than one shot is needed for long-term protection. Check with your doctor or nurse to determine how many shots are needed and when to return for the next dose. The vaccine provides protection about four weeks after the first injection; a second injection protects you longer, possibly up to 20 years. Twinrix, a combined hepatitis A and B vaccine may be given to those over 18 years of age."