You woke up suddenly feeling awful: a fever out of nowhere, aching muscles, and a cough you didn't have yesterday. You've heard flu B is spreading late this season and you're wondering if that's what hit you. Here's the reassuring part: for most healthy people, flu B looks and feels just like any other flu, and you'll likely recover within about a week.
This guide walks you through the symptoms of influenza B in 2026, how it compares to flu A, how long it tends to last, and the warning signs that mean it's time to call a clinician.
What are the symptoms of flu B?
Flu B symptoms are clinically identical to flu A. There is no separate "flu B symptom set" you can spot on your own, and the only way to confirm which type you have is a lab test ordered by a clinician. Influenza of any type tends to come on abruptly, unlike a cold that builds slowly over days.
Common influenza B symptoms include:
- Sudden fever or feeling feverish, often above 100.4°F (38°C), with chills
- Muscle and body aches
- Headache
- Dry, persistent cough
- Sore throat
- Runny or stuffy nose
- Fatigue and weakness
- Vomiting and diarrhea (more common in children than adults)
Flu B vs flu A: what's the difference?
The two types are caused by different influenza viruses, but case by case they are impossible to tell apart without testing. The differences are mostly in how the viruses behave at a population level, not in how your symptoms feel.
A few practical distinctions:
- In a typical season, flu A causes most cases and flu B a smaller share. This season followed that pattern: from late September 2025 through mid-February 2026, U.S. labs reported influenza A in about 85% of positive specimens and influenza B in about 15%.
- Flu A can infect humans, birds and pigs and mutates quickly, which is why new strains emerge. Flu B only infects humans and changes more slowly.
- Adults are more likely to get flu A, while children are more likely to get flu B.
- In children, influenza B is linked to more seizures, vomiting and diarrhea, while influenza A is linked to more ear infections.
Why is flu B spreading in spring 2026?
If you're getting sick with flu later than expected this year, that fits the pattern. Influenza B characteristically peaks later in the season than flu A. During the 2025–2026 season, influenza A(H3N2) dominated early, but flu A activity then fell while flu B activity climbed nationally into late February 2026 and the spring, with influenza B increasingly reported in later weeks.
Only one flu B lineage circulates today. B/Victoria is the seasonal strain, and the older B/Yamagata lineage has not been detected anywhere since March 2020; CDC reported no B/Yamagata cases this season. The 2025–2026 U.S. flu vaccine is built to protect against one B/Victoria virus along with A(H1N1) and A(H3N2).
How long does flu B last?
Most otherwise-healthy people recover from flu B in about a week. Fever and the worst body aches usually ease within a few days, but a lingering cough and fatigue can hang on for one to two weeks after the rest of the symptoms fade. That tail end is normal and does not mean the infection is getting worse.
Rest, fluids, and time do most of the work. If you're at higher risk, for example if you're pregnant, over 65, very young, or have a chronic condition like asthma, heart disease, or a weakened immune system, antiviral medication can help. Antivirals work best when started early, ideally within the first day or two of symptoms, so contact a clinician promptly if you fall into one of those groups.
When to see a doctor or seek emergency care
Most flu B cases can be managed at home, but some symptoms signal a medical emergency. Flu is not something to dismiss: CDC classified the 2025–2026 season as moderate overall, with high severity in the pediatric age group, and as of its Week 7 report (data through February 21, 2026) estimated at least 25 million illnesses, about 330,000 hospitalizations, and roughly 20,000 deaths, including 79 reported pediatric deaths this season.
Get emergency care right away for any of these warning signs:
- Difficulty breathing or shortness of breath
- Persistent pain or pressure in the chest or abdomen
- Persistent dizziness, confusion, or trouble waking up
- Seizures
- Not urinating or signs of dehydration
- Severe muscle pain or weakness
- Symptoms that improve, then return with worse fever or cough
- In children: fast or labored breathing, bluish lips, no tears when crying, or unusual irritability
Medical Disclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult with a qualified healthcare provider before starting any new skincare treatment, especially if you have underlying health conditions, are pregnant, or are taking medications.
