"Getting a booster is the best possible defence against COVID for you and your family," said the Liverpool captain, who is also an NHS Charities Ambassador.
Alisson added: "Help keep everyone safe and join me and get boosted now."
The duo's calls for fans to protect themselves and others come after their head coach Klopp shared his experience of having the third jab.
"I have no issue telling you I received my booster jab as soon as I was eligible," said Klopp. "[And] Again that will be the case for many if not nearly all within our ranks in the coming days and weeks."
"We have to save a lot of people and then we are together, we are a match," he said. "If a lot of players are vaccinated, COVID doesn't come.
"The booster is the most important thing to save you and your family. I mean everything, the first, the second and the booster."