Ram also said the United States Open should only proceed if all qualified players are able to travel to the Grand Slam.
Professional tennis was suspended in early March as countries went into lockdown to contain the spread of the virus and the season will not resume until early August.
Wimbledon was cancelled for the first time since World War Two while the French Open was postponed to September.
A decision is expected to be taken this month.
“I don’t see players feeling 100 percent safe without a vaccine because there would always be a risk of contracting the virus,” Ram, who won his first Grand Slam men’s doubles title at the Australian Open this year, said.
“I don’t think the United States open or any event will take place if a certain number of players feel uncomfortable or unsafe while playing.”
Media reports have said the United States Tennis Association (USTA) is considering flying players in by chartered flights and hosting the tournament with no fans in attendance.
“We can’t have the United States Open until everyone who has qualified for the event is in a position to travel to the event.
“Until that happens, we are going to be at a standstill,” said Ram, who also won the Olympic silver in mixed doubles in 2016.