Flu B symptoms typically last five to seven days for most healthy people. The worst of it, including fever, body aches, and headache, usually peaks in the first three days and then gradually eases. However, a lingering cough and fatigue can stick around for two weeks or longer, which catches many people off guard even though it’s completely normal.
Day-by-Day Symptom Timeline
Flu B follows a fairly predictable pattern once symptoms appear, which is usually one to four days after you’re exposed to the virus.
Days 1 through 3 are the roughest stretch. Fever, headache, muscle pain, and weakness hit suddenly, often alongside a dry cough, sore throat, and nasal congestion. This is when most people feel too sick to do anything but rest. It’s also the period when you’re most contagious.
Day 4 is typically the turning point. Fever and muscle aches start to fade, but your throat may feel hoarse and your cough can actually become more noticeable as the upper respiratory symptoms take center stage. Many people describe feeling “flat” or wiped out even though the worst pain is behind them.
Days 5 through 7 bring continued improvement. Most of the acute symptoms resolve during this window. You’ll likely feel functional again, though not fully yourself.
Day 8 and beyond is where lingering effects show up. A dry cough and tiredness can persist for one to two weeks after the main illness resolves. For older adults and people with chronic lung conditions, that cough and general fatigue can stretch even longer.
How Long You’re Contagious
You can spread flu B to others starting about one day before your symptoms even appear, which is part of why the virus spreads so effectively. You remain contagious for five to seven days after getting sick. Young children and people with weakened immune systems may shed the virus for longer than that.
The most contagious window is the first three days of illness, when viral levels are highest. Current CDC guidance says you can return to work, school, or public activities once both of these are true: your symptoms are improving overall, and you’ve been fever-free for at least 24 hours without using fever-reducing medication.
Why the Cough and Fatigue Linger
Even after your immune system clears the virus, the inflammation it caused in your airways takes time to heal. That’s why a dry, nagging cough can hang on for two weeks or more. It doesn’t mean you’re still sick in the traditional sense, and it doesn’t necessarily mean you’re still contagious. Your body is just repairing the damage.
Post-viral fatigue works similarly. Fighting off the flu demands enormous energy from your immune system, and it’s normal to feel drained for a week or two after your fever breaks. This is especially common in older adults. Pushing back to a full schedule too quickly can make the fatigue feel worse, so easing back into your routine over several days is a practical approach.
Recovery for Higher-Risk Groups
Most people recover from flu B within a few days to two weeks, but the timeline stretches for certain groups. Adults 65 and older face a harder recovery partly because the immune system weakens with age. While the body is focused on fighting the flu, it becomes more vulnerable to secondary infections like pneumonia, which can extend the illness by weeks.
People with chronic conditions like asthma, diabetes, heart disease, or kidney disease are also at greater risk for complications that delay recovery. The same applies to residents of nursing homes or long-term care facilities. For children, flu B can sometimes hit harder than flu A, and their contagious period may run longer than the typical five-to-seven-day window.
Can Antivirals Shorten Recovery?
Prescription antiviral medications can trim about a day off your illness if started early enough. The key is timing: the biggest benefit comes when treatment begins within 48 hours of symptom onset. One clinical trial found that even starting antivirals at the 72-hour mark still reduced symptoms by roughly one day compared to no treatment.
For flu B specifically, one newer antiviral has shown a meaningful advantage, cutting the time to symptom improvement by more than 24 hours compared to older options. Antivirals aren’t necessary for every flu case, but they make the biggest difference for people at high risk of complications.
Signs the Flu Isn’t Resolving Normally
The pattern to watch for is improvement followed by a setback. If your fever or cough gets better and then returns or worsens, that’s a warning sign of a secondary complication like pneumonia or a bacterial infection. In children, a fever above 104°F that doesn’t respond to fever-reducing medication also warrants prompt medical attention.
Straightforward flu B, even when it feels miserable, follows a clear arc: rapid onset, peak misery for a few days, then steady improvement. If that arc reverses at any point, or if you develop difficulty breathing, chest pain, or confusion, those are signals that something beyond the original virus needs attention.