USCIS officers use Form I-693, Report of Medical Examination and Vaccination Record, to determine whether an applicant for an immigration benefit in the United States is inadmissible under the health-related grounds of inadmissibility. By specifying that the Form I-693 must be signed no more than 60 days before the applicant files the underlying application for which Form I-693 is required, the validity of the form is more closely tied to the timing of the underlying application.
Additionally, requiring submission of a Form I-693 that was signed no more than 60 days before the date the underlying application was filed may, in some cases, maximize the period of time Form I-693 will be valid while the underlying application is under USCIS review. Officers will still have the discretion, as they have always had, to request a new Form I-693 if they have reason to believe an applicant may be inadmissible on the health-related grounds. Delays in adjudicating the underlying application will also be reduced if fewer requests for updated Forms I-693 are necessary.
Source: www.uscis.gov