Both Influenza A And B Are Extremely Contagious, And The Shot Helps Protect Against Both
The flu virus is no joke. The 2019-2020 flu season left 38 million people sick with the influenza virus, which resulted in 18 million visits to a health care provider, 400,000 hospitalizations, and 22,000 flu deaths, according to the Centers for Disease Control and Prevention (CDC). And this year's flu season is fully underway, so you may have questions about the main types that you hear about each season: influenza A and B.
The flu can be kind of confusing because there are actually four types of influenza viruses: A, B, C and D. But for humans, it's influenza A and B that cause seasonal epidemics every winter and spring that are what you know as "flu season." Typically, influenza A is more common. But in early 2020, influenza B cases were highly prevalent, according to the CDC.
"The majority of influenza during the flu season is influenza A, but influenza B has been increasing in the last year, and some studies show more severe influenza B illness in children," says Kavita Shanker-Patel, MD, a family medicine physician at Northwestern Medicine Central DuPage Hospital.
So what are the differences between influenza A and B, and what do flu B symptoms look like? Here's what you need to know.
What is influenza B—and how is it different than influenza A?
Both influenza A and B are very contagious and have comparable rates of infection and death. But influenza A and B have some key differences that determine how prevalent they tend to be.
Influenza A: "Influenza A is a more common and faster-changing strain of influenza virus," says Dr. Shanker-Patel, which is part of the reason it spreads so easily and tends to be the dominating strain during flu season, responsible for the majority of infections. Influenza A has subtypes, which are classified based on the combo of these two proteins found on the surface of the virus: hemagglutinin (H1-H18) and neuraminidase (N1-N11). The two main circulating A subtypes in humans, says Dr. Shanker-Patel, are A(H1N1) and A(H3N2).
Influenza B: Influenza B is normally less common and a more slowly changing strain of influenza. It gets classified under two lineages: B(Victoria) and B(Yamagata), says Dr. Shanker-Patel. With influenza B, people can be contagious days before the onset of symptoms, she notes. (In general with the flu, people are contagious about a day before symptoms pop up and while they are showing symptoms, per the CDC.)
Another difference between the two: B is found only in humans, while A can be found in other species like birds and pigs, according to Dr. Shanker-Patel.
Oh, and flu season usually involves strains of both flu types (and the flu vaccine is designed to protect against specific strains of both, depending on which A and B strains vaccine developers predict circulating that season). For example, "The 2019-2020 influenza season in the northern hemisphere was predominately influenza B/Victoria and influenza A(H1N1)pdm09," says Dr. Shanker-Patel.
What are the symptoms of influenza B?
The symptoms on influenza B are pretty similar to influenza A, with a few distinctions:
Fever
Chills
Cough
Sore throat
Runny/stuffy nose
Body aches (these are thought to be more predominate with influenza B)
Headaches
Fatigue
GI symptoms, like vomiting and/or diarrhea (this tends to be the case more often in children with influenza B)
What does treatment for influenza B typically involve?
The treatments for influenza B and A are also pretty similar. You can use prescription meds to help shorten the duration of your illness, as well as other medication and lifestyle changes to lessen the intensity of your symptoms.
Antiviral medication: "These help to lower the duration of symptoms, and can help prevent serious complications," says Dr. Shanker-Patel. There are currently 4 FDA-approved flu antivirals.
Over-the-counter fever reducers: "These are for fever control, and other symptoms," says Dr. Shanker-Patel, and include nonsteroidal anti-inflammatory drugs like NSAIDs (Advil) and acetaminophen (Tylenol).
Lots of rest and hydration
Staying home
Do I need to be worried about preventing influenza B specifically?
While the flu is serious, you don't need to focus on preventing a specific strain of it. You just want to make sure you are using good hygiene and preventive practices (psst, mask wearing and social distancing are great for avoiding a flu too!) overall to avoid contracting any and all infectious diseases circulating right now. "Although influenza A is more rapidly changing and more prevalent, influenza B can cause just as severe, or more severe illness," says Dr. Shanker-Patel. "So it’s important to practice these measures to reduce risk of contracting both types of influenza virus."
Safety measures are especially important during this 2020-2021 flu season, which overlaps with the COVID-19 pandemic. According to the CDC, some of the symptoms of flu and COVID-19 are similar, making it hard to tell the difference between them based on symptoms alone. But diagnostic testing can determine if you are sick with a flu or COVID-19.
How do you stay safe from the flu again in general?
First, get your flu shot. "The flu shot is the most important step in preventing influenza," says Dr. Shanker-Patel. While getting it doesn't guarantee you won't get the flu, it reduces your chances, protects groups who cannot get a flu shot and are at risk of developing serious complications or dying from the flu, and reduces your chance of requiring hospitalization for the flu. Beside that, you should also:
Avoid close contact with sick people
Cover your coughs and sneezes (and following CDC recommendations regarding mask wearing!)
Wash your hands with soap and water often throughout the day
Try not to touch your face
Stay on top of the cleaning and disinfecting of surfaces, especially in frequently touched areas
The bottom line: Influenza A and B are both highly contagious in humans and have similar symptoms. Getting your flu vaccine and taking other preventive measures help protect you against both.
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