Translation:Because of the cold weather, Sofia got sick.
It makes you more likely to be inside, being exposed to more people in a smaller area. It also increases sexual desire, opening you up to a slightly increased chance of STIs.
When in a cold environment, the body prioritizes it's energy on keeping warm. This means that it would not exert as much energy on other functions- such as the immune system.
Additionaly, being cold for an extended period of time makes it more difficult to sleep. This could lead to chronic fatigue, which as well, lowers your immune system.