A mark on the forehead or the hand is where one will receive the mark of the beast.
Satan wants us deceived. He also twists the Holy Scripture. So how better to do this than to get a bunch passionate but scripturally illiterate zealots to start reinventing unscriptural conclusions about the Mark of the beast. So when it really comes along everyone will say well this isn’t it because it was a vaccine.
Revelation 14
9 Then a third angel followed them, saying with a loud voice, “If anyone worships the beast and his image, and receives his mark on his forehead or on his hand,
10 “he himself shall also drink of the wine of the wrath of God, which is poured out full strength into the cup of His indignation. He shall be tormented with fire and brimstone in the presence of the holy angels and in the presence of the Lamb.
11 “And the smoke of their torment ascends forever and ever; and they have no rest day or night, who worship the beast and his image, and whoever receives the mark of his name.”