Mass. Gen. Laws ch. 111, § 183

Any person over eighteen presenting a certificate, signed by the register of a probate court, that he is under guardianship shall not be subject to section one hundred and eighty-one; and any child presenting a certificate, signed by a registered physician designated by the parent or guardian, that the physician has at the time of giving the certificate personally examined the child and that he is of the opinion that the physical condition of the child is such that his health will be endangered by vaccination, shall not, while such condition continues, be subject to the two preceding sections.