(a) Any employee who was a member in service at the time of sustaining an injury or undergoing a hazard on account of which he becomes entitled to payments under the provisions of chapter one hundred and fifty-two shall, during the period while he is receiving weekly payments for total incapacity under the provisions of sections sixty-nine to seventy-five, inclusive, of such chapter or of sections thirty-four, thirty-four A, thirty four B, thirty-five A, thirty-five F or thirty-six of such chapter in the case of an employee of the Massachusetts Department of Transportation, the Massachusetts Port Authority, the Greater Lawrence Sanitary District, the Blue Hills Regional Vocational School system, or the Minuteman Regional Vocational Technical School District, or during any period determined, as set forth, in paragraph (c), represented by the allocation of the amount of any lump sum settlement payable directly to him under the provisions of section forty-eight of such chapter in lieu of such weekly payments and also, in either event, during a further period of thirty days, retain all the rights of a member in service while he is living, unless and until a retirement allowance becomes effective for him under the provisions of sections one to twenty-eight, inclusive. During such periods, however, no deductions for the annuity savings fund of the system shall be made from payments such members shall receive under the provisions of chapter one hundred and fifty-two nor shall he withdraw his accumulated total deductions therefrom. Any such member shall have credited to him as creditable service under the system the period during which he is receiving such weekly payments or lump sum settlement in lieu of such weekly payments. The board of each system shall keep an annual record of all such creditable service. At the time of his retirement there shall be transferred from the pension fund of the system of which he was a member at the time of the accident, to the annuity savings fund of the system of which he is then a member, the amount which said person would have paid into said fund had his employment in the service of the commonwealth or political subdivision thereof not been interrupted by his industrial accident with regular interest to the date of retirement, but in no event more than would be credited to him if regular deductions with interest were made on his full salary or wages; provided, that any sum so paid by the commonwealth or any political subdivision thereof shall be used only to provide an increased retirement allowance of the person on whose account such payment is made. Any period during which an employee is receiving weekly benefits for total incapacity under chapter one hundred fifty-two shall not be counted in computing such employee's sick leave for severance pay purposes; nor may an employee use sick leave accrued during the time of total incapacity during such total incapacity.