Flu B is treated the same way as flu A: rest, fluids, fever management, and in many cases, prescription antiviral medication. Most people recover within one to two weeks, but the first 48 hours after symptoms appear are critical if you want antiviral treatment to make the biggest difference.
The 48-Hour Window for Antivirals
Prescription antiviral drugs are the most effective tool for shortening a flu B infection, and timing matters more than anything else. Clinical benefit is greatest when you start treatment within 48 hours of your first symptoms. Multiple large analyses of clinical trials confirm that early treatment reduces the duration of both fever and overall illness compared to no treatment at all.
Two main antiviral options exist. The more common one (oseltamivir, sold as Tamiflu) is taken twice daily for five days as a pill or liquid. The newer option (baloxavir, sold as Xofluza) is a single-dose pill. For flu B specifically, baloxavir reduced the time to symptom improvement by more than 24 hours compared to oseltamivir in a randomized trial. That makes it a particularly strong choice when flu B is confirmed.
If you’ve missed the 48-hour window, antivirals can still help, though the benefit is smaller. One study in children found that starting oseltamivir even at 72 hours after symptom onset still shortened symptoms by about a day. For people at high risk of complications, including young children, adults 65 and older, pregnant women, and anyone with a chronic condition like asthma or diabetes, doctors typically prescribe antivirals regardless of timing.
Managing Fever and Body Aches
Flu B typically causes high fever, intense body aches, headache, and fatigue. Over-the-counter pain relievers and fever reducers are your first line of comfort. Acetaminophen (Tylenol) and ibuprofen (Advil, Motrin) both work well for bringing down fever and easing muscle pain. If you’re taking acetaminophen, keep your total daily intake under 4,000 milligrams to protect your liver. This is especially important if you’re also taking a multi-symptom flu product, since many of those already contain acetaminophen.
For children and teenagers, never use aspirin during a flu infection. Aspirin has been linked to Reye’s syndrome, a rare but serious condition where the liver swells, blood sugar drops, and the brain can develop dangerous swelling. Symptoms of Reye’s syndrome typically appear three to five days after the viral infection begins and can include persistent vomiting, unusual sleepiness, and confusion. Stick with acetaminophen or ibuprofen for kids.
Staying Hydrated
Fever, sweating, and reduced appetite can dehydrate you quickly during the flu. Under normal conditions, men need roughly 15 cups of fluid per day and women need about 11 cups, and illness pushes those needs higher. Water is fine, but drinks with electrolytes or oral rehydration powders that combine salt and sugar can help your body absorb fluid more efficiently.
If nausea or vomiting makes it hard to keep fluids down, take small sips of about 30 milliliters (roughly two tablespoons) every three to five minutes rather than trying to drink a full glass at once. Broth, diluted juice, and popsicles all count toward your fluid intake. Watch for signs of dehydration: dark urine, dry mouth, dizziness, or going many hours without urinating.
Rest and Recovery Timeline
Most flu B symptoms peak in the first two to four days, with fever often breaking within five days. Cough and fatigue tend to linger longer, sometimes for two weeks or more. There’s no way to speed this part up beyond giving your body the rest it needs. Sleep as much as you can, especially in the first few days.
You’re contagious starting about one day before symptoms appear and for five to seven days after getting sick. The first three days of illness are when you’re most likely to spread the virus. Young children and people with weakened immune systems may be contagious even longer. Stay home until you’ve been fever-free for at least 24 hours without using fever-reducing medication.
Warning Signs That Need Emergency Care
Most flu B infections resolve on their own, but some develop into serious complications. In adults, seek emergency care for:
- Difficulty breathing or shortness of breath
- Persistent chest or abdominal pain or pressure
- Confusion, dizziness, or difficulty staying awake
- Not urinating (a sign of severe dehydration)
- Seizures
- Fever or cough that improves, then returns worse
In children, watch for fast or labored breathing, ribs pulling in with each breath, bluish lips or face, refusal to walk due to muscle pain, or no urine output for eight hours. Any fever in an infant under 12 weeks old during flu season warrants immediate medical evaluation. A fever that breaks and then spikes again, or a cough that clears up and comes back worse, can signal a secondary bacterial infection like pneumonia.