Alexander Gintsburg, director of the Gamaleya Institute which developed the vaccine, said in April that the gap between the shots could be increased to 90 days.
The RDIF official quoted Gamaleya trials as showing longer gaps had secured a better immune response, but provided no further details of the trials. The official issued the statement after a Reuters request for comment, and denied it was related in any way to Russian deliveries of Sputnik V.
RDIF has notified all foreign partners and vaccine buyers that prolonging the gap between doses to 90 days helps to slightly increase the immune response, the official said.