Influenza A vs. B: What's the Difference?
Blue Daily
| 3 min read
As Americans have experienced difficult flu seasons in recent years, you may wonder about the difference between influenza A and influenza B and what you can do to stay healthy this winter.
Flu levels in the U.S. were as high as they’ve been in 15 years across the 2025-2026 flu season, according to the U.S. Centers for Disease Control and Prevention (CDC). There have been an estimated 32 to 57 million illnesses, up to 800,000 hospitalizations and as many as 81,000 deaths from flu so far, per the CDC.
As we head into the fall months, it's good to be proactive ahead of the 2026-2027 flu season. Part of being proactive is analyzing flu a vs. b to understand the difference.
Influenza A vs. B: What is the difference?
There are four types of influenza viruses: A, B, C and D. C causes only a mild respiratory illness, and D is not known to infect humans, narrowing the flu strains you need to protect yourself against to A and B.
Influenza A is much more common than influenza B, making up more than 90% of cases in 2024, according to the Cleveland Clinic. These flu types are distinguished by key differences, the most important of which is type B only infects humans, while type A can infect humans and animals. This makes influenza A more dangerous because inter-species transmission can lead to new flu strains, which can then lead to seasonal epidemics and pandemics. Bird flu is an example of this, as it emanates from flu A.
Influenza A is more common in adults, and Influenza B is more common in children, because they have underdeveloped immune systems and less immunity to the virus than adults. Type B can cause complications that sometimes lead to hospitalization or death in children, according to the CDC.
Timing is also a key way to differentiate flu A and flu B, the latter of which usually makes you sick toward the tail end of flu season because it mutates more slowly than flu A. Because of slower mutation, Influenza B strains do not vary from year to year as much as Type A strains.
What do influenza A and influenza B have in common?
Influenza A and B do share a few characteristics, including:
- They spread the same way and cause similar symptoms like:
- Diarrhea and vomiting (usually only in children)
- Fever/chills
- Headaches
- Muscle and body aches
- Runny of stuffy nose
- Sore throat
- Weakness and fatigue
Both flu strains are more likely to affect babies and older adults, causing more serious symptoms in these age groups.
Healthcare providers treat flu A and flu B the same way. So, if you’re asking yourself, “how do I know if I have influenza A or B?” it isn’t that important for recovery as the treatment is the same. For either virus, providers will recommend rest, drinking plenty of fluids, taking over-the-counter medications and getting vaccinated.
Get vaccinated to protect against the flu
Getting the shot is the best way to prevent a potentially deadly disease. Vaccines have been proven to lower the risk of severe illness and death resulting from the flu.
Flu shots are recommended every year for individuals ages 6 months and older. The best time to get a flu vaccine is September or October, but it’s certainly not too late to get one in February or March, especially considering how deadly this year’s flu season is. As we are seeing now, flu sicknesses often hit their second peak in February.
Flu shots are available at pharmacies, primary care offices, urgent care centers, health departments and clinics. Workplaces, schools and colleges often host vaccination events. You can find places to get a flu shot by visiting vaccines.gov.
Additionally, practice flu prevention by washing your hands, avoiding close contact with people who are sick and covering your mouth when you sneeze or cough.
Photo credit: Getty Images
