Can I be reimbursed for purchasing social security after finding out a major illness?

You can't. Social security needs to be paid for half a year to be reimbursed.

Social medical insurance reimbursement is after discharge or transfer.

Settlement procedures for inpatient and outpatient treatment of special diseases:

Designated medical institutions should report the expense list, hospitalization list and related materials of patients discharged from hospital last month to the medical insurance agency before 10 every month, which will be used as the basis for monthly pre-allocation and year-end final accounts after examination;

The medical insurance agency pre-allocated the hospitalization and outpatient co-ordination expenses for special diseases last month;

Insured persons who have been identified as suffering from special diseases shall go to the designated medical institutions designated by the labor and social security departments for medical treatment and medicine purchase, and the medical expenses incurred shall be directly recorded and settled immediately.

Emergency settlement procedure: the medical expenses incurred by the insured in emergency rescue to non-designated medical institutions in the city and medical institutions in different places shall be paid in advance by individuals or units. After the emergency rescue, the medical insurance agency shall go through the reimbursement procedures according to the provisions with the hospital emergency medical records, inspections, laboratory tests, invoices and detailed list of medical expenses.