A living area should ideally be heated to around 64°F. Less than this and your body will have to start working to keep your main organs at their desired temperature of around 100°F
If the temperate drops to 32°F, you can start to shiver as the body attempts to work maintain core temperatures.
Cognitive tasks may take longer as there is less blood being delivered to the brain.
Your heart will beat faster and your blood pressure will rise which is why more people have strokes and heart attacks in winter.
Cold air contains less moisture and it is moisture that can trap viruses. When people meet up indoors in winter, they do so in rooms where windows are closed and there is less air circulating which also helps spread virus.