Newborn around flu

Helpppppp my son is 4 months old and his older brother who is 4 had been kissing all over him and just now spiked a fever of 103. Idk if it’s the flu but that’s what I’m thinking . 😩😩 I’m scared my newborn is gonna get it . And the flu for newborns can be fatal . Anyone ever have a newborn have the flu?!