Flu A vs. Flu B: What is the Difference?

December 5, 2022

We are in the midst of a never-seen-before public health crisis. Not only are we dealing with a surge of COVID-19 and RSV, a respiratory virus that primarily affects infants and young children, but we could experience one of the worst influenza (flu) seasons in decades.

According to the CDC’s FluView data, 44 states report “high” to ”very high” flu-like activity levels. The flu positivity rate in L.A. County alone has reached 25%, a level not seen at this time of year in the last four years. Further, the number of flu hospital admissions reported to HHS almost doubled compared to the previous week. 

So far this season, there have been an estimated 8.7 million illnesses, 78,000 hospitalizations, and 4,500 deaths from flu.

Of the flu A viruses detected and sub-typed, 79% have been flu A (H3N2), and 21% have been flu A (H1N1). Flu A accounts for 99.1% of the cases, whereas Flu B is at .09%.

So what does this data mean exactly? What is the difference between flu A and B, and why is it important to test for both? Let's take a closer look.

Every year, millions of people worldwide become infected with the flu. On average, the flu causes more than 200,000 hospitalizations and thousands of deaths annually in the United States. The flu is a serious illness, and while there are many different types of flu viruses (A, B, C, and D), type A (H3N2) is the most common and can cause more severe disease than the others. In addition, type A can also lead to pandemics due to its dynamic, mutating nature and extensive host range.

Some of the subtypes of flu A that have caused the most significant number of known human deaths are:

Flu A virus is divided into subtypes based on two proteins on its surface: Hemagglutinin (H) and neuraminidase (N). There are 18 different H subtypes and 11 different N subtypes, which could theoretically have 198 combinations, but 131 have been identified. Because flu A viruses are constantly changing, similar to SARS-CoV-2, creating a vaccine that offers long-lasting protection can be challenging. 

There are several differences between flu A and B: While flu A can infect humans and animals, flu B only infects humans; Flu B contains only one type of H protein (H1N1) and mutates about two to three times more slowly than flu A. For this reason, creating a vaccine for flu B, classified into two lineages: B/Yamagata and B/Victoria, is much easier.

The most critical difference between the two types is their severity. Flu B is believed to be a milder virus compared to some strains of influenza A, such as H3N2, but more potent than the influenza A strains like H1N1. While most confirmed infections during flu season will be flu A, flu B infections can increase late in the season, as seen in 2017 to 2018, and can trigger a range of serious health conditions.

Both types of the flu can be difficult to diagnose based on clinical signs and symptoms alone because they can be similar to those caused by other infectious agents, including, but not limited to, SARS-CoV-2, adenoviruses, respiratory syncytial viruses (RSV), Mycoplasma pneumoniae, rhinoviruses, parainfluenza viruses, and Legionella spp. 

Therefore, robust molecular testing at the first sign of any symptom is key to determining which respiratory virus you have. With specific and accurate test results, healthcare providers can treat you with the proper antiviral medications that work best when taken within 48 hours of symptom onset. Early testing and treatment are especially important for high-risk individuals, including children under 59 months, the elderly, pregnant women, or those with chronic medical or immunosuppressive conditions.

Flow Health offers a multiplex real-time RT-PCR test for detecting and differentiating SARS-CoV-2 (COVID-19), flu A, and flu B. The capability to test from a single sample means reduced discomfort and repeated testing for patients and less time and resources for clinics. Our fast results-reporting platform provides results within 24 hours. These results can be accessed by the patient or the provider in our online portal. 

 To schedule a test or for more information, contact cs@flowhealth.com.

FDA Instructions and Fact Sheet:

IFU: https://www.fda.gov/media/145931/download

Fact Sheet: https://www.fda.gov/media/145930/download

related blog posts