It makes itself a little "rubbery" coat, as the BBC reports:
Scientists believe they have uncovered a key reason why flu viruses tend to strike in cold weather.
They found the viruses coat themselves in fatty material that hardens to a gel, protecting them in the cold.
This coating melts in the higher temperatures of the respiratory tract, allowing the virus to infect cells. . . .
The hard rubbery coating around the virus which forms in colder temperatures gives it the protection it needs to pass from person to person. The coating is so robust it can even resist to certain detergents.
However, once inside a host the virus can only infect a target cell once the coating has melted.
But this liquid phase is not tough enough to protect the virus against the elements, and so if the protective coating melts when the virus is outside the host, it dies.
So a summer cold IS a different animal.