Section 36D. Vaccinated animals which are over eighteen months of age may be imported into the commonwealth if within thirty days prior to entry they have reacted negatively to an approved blood test conducted in a laboratory approved by the state of origin. Vaccinated animals eighteen months of age and under may be imported into the commonwealth without such blood test if accompanied by a certificate stating the animals have been vaccinated between the ages of four to eight months, inclusive, by a veterinarian duly licensed by the state of origin of said animals.