Symptoms of the flu can range from mild to severe, and include:
- Fever
- Chills
- Cough
- Sore throat
- Runny or stuffy nose
- Muscle aches
- Headaches
- Fatigue
- Vomiting and diarrhea (though the GI symptoms are more common in children)
Flu is mostly spread through the air by tiny droplets generated when infected people cough, sneeze, or talk, which can then go on to land in the mouths or noses of others. It can also be spread by contact with objects — if a person touches something with the flu virus on it and then touches their nose or mouth — though that’s less common.
As with a cold, you can shed the flu virus and infect other people up to 24 hours prior to onset of symptoms, says Winslow. “You’re most contagious the first day or two after the onset of symptoms,” he says.
By day three or four, you may still have a lot of symptoms as a result of your immune system being activated, but the amount of virus that you’re shedding is lower, he says. “Even though it’s less likely to spread by that point, you are still potentially contagious. To be safe, I would recommend that people wear a mask pretty much the whole time they have upper respiratory symptoms,” says Winslow.
The flu shot can reduce your chances of getting the flu. If you do get the flu even after getting immunized, it’s less likely that you’ll become severely ill.
There isn’t enough evidence to show that already being vaccinated against the flu influences how long you’ll be contagious if you do still get the virus, says Winslow.
But a medication such as Tamiflu (oseltamivir) taken within the first 48 hours after onset of symptoms probably does make you less contagious, says Winslow. “It definitely reduces the duration of symptoms and also very likely has at least a modest effect on reducing viral shedding because it is an antiviral,” he says.