Increasing the interval between doses of a multidose vaccine
does not diminish the effectiveness of the vaccine.

Decreasing the interval between doses of a multidose vaccine
may interfere with antibody response and production.

Some people do not have good vaccination records. Only written
and dated vaccination records can be accepted as evidence of
vaccination. If a person's records cannot be located, vaccinate
according to the recommended schedule. Or, the healthcare
provider may order a serologic test to see whether the person
already has immunity.