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Influenza A vs. B: Which is worse?

Influenza A vs. B causes | Prevalence | Symptoms | Diagnosis | Treatments | Risk factors | Prevention | When to see a doctor | FAQs | Resources

It starts small. You might wake up with an annoying throat tickle and a runny nose, or you might feel a little more groggy throughout the day than usual. But there’s more on the way. You come down with a fever, chills, body aches, and you’re couch-ridden with the flu. 

“The flu” has become a broad term that people use to incorrectly describe a wide range of illnesses. We often hear people say “oh, I came down with the stomach flu last week,” or “the kids got the 24-hour flu.” But “flu” refers to four types of influenza viruses (A, B, C, and D), most prominently influenza A and influenza B. 

Influenza A can infect humans and animals. In most cases, it’s associated with seasonal epidemics in the United States (aka “flu season“) and global pandemics. It’s always changing, so it has various subtypes, including the infamous bird flu (avian influenza) and swine flu. On the other hand, influenza B has two subtypes (Victoria and Yamagata), which occur, for the most part, only in humans and mutate slower, so it’s not really a pandemic risk. 

Read on for a complete guide to these two types of flu viruses.

Causes

Influenza A

The most common form of transmission is through tiny droplets created when an infected person talks, sneezes, coughs, or breathes heavily. Type A is also (albeit very rarely) contracted via contact with an infected animal, like a bird or pig. Influenza can also be transmitted through inanimate objects if a sick individual contaminates it, such as a doorknob. 

Influenza B

Like influenza A viruses, influenza type B is primarily transmitted through contact with the droplets when an infected individual coughs, sneezes, or talks. Animals aren’t usually susceptible to the influenza B virus, so generally aren’t considered to be carriers. 

Influenza A vs. B causes

Influenza A Influenza B
  • Contact with droplets from an infected individual
  • Contact with infected animals (rare)
  • Contact with droplets from an infected individual

RELATED: Is the flu airborne? Learn how the flu spreads

Prevalence

Influenza A

Influenza A is the most common type of flu. It accounts for approximately 75% of total flu virus infections, and it’s the most likely cause of the “seasonal flu” that hits the U.S. every winter. That’s not a small number, especially considering the 25 to 50 million cases nationwide every year

During the 2018-19 flu season, the Centers for Disease Control and Prevention (CDC) tested 1,145,555 specimens for influenza, and of the 177,039 positive results, 95% were influenza A. 

Influenza A is further broken down into subtypes based on two proteins on the surface of the virus called hemagglutinin and neuraminidase. The subtypes of both of these proteins result in many different possible combinations and unique influenza A viruses. In addition, small genetic mutations that cause changes in these surface proteins over time may allow these strains to improve their ability to infect people each season. This characteristic presents challenges in predicting a predominantly circulating influenza A virus when it comes to deciding on the composition of the influenza vaccine months before the actual flu season hits. All of these factors together contribute to the predominance of influenza A virus infection each season. 

Influenza B

Of course, numbers and percentages can vary from season to season. For example, the early stages of the 2019-2020 influenza season saw influenza B as the most common type, especially among children. 

But most years, it takes a backseat to type A. It doesn’t spread quite as easily because it mutates slower and only has two main subtypes: Victoria and Yamagata. On average, though, type B infections account for around 25% of total flu cases. 

Influenza A vs. B prevalence

Influenza A Influenza B
  • Around 75% of all influenza cases (on average)
  • About 25% of all influenza cases (on average)
  • More common and severe among children

Symptoms

Influenza A

Symptoms of influenza A tend to be similar regardless of subtype. The most common are runny nose, sore throat, fever, chills, body aches, and fatigue.

The main difference is their severity. Type A symptoms often come on stronger and sometimes result in hospitalization or even death. According to CDC.gov, influenza A accounted for 95.5% of all seasonal influenza hospitalizations during the 2018-19 season.

Influenza B

Type B causes similar symptoms to the ones listed above, but they’re usually milder. However, it still has the potential to increase in severity, causing hospitalization and death, particularly in children

Influenza A vs. B symptoms

Influenza A Influenza B
  • Runny nose
  • Sore throat
  • Fever
  • Chills
  • Body aches
  • Cough
  • Headaches
  • Fatigue
  • Chest discomfort
  • Runny nose
  • Sore throat
  • Fever
  • Chills
  • Body aches
  • Cough
  • Headaches
  • Fatigue
  • Chest discomfort

(Symptoms can be less severe than influenza A)

RELATED: Coronavirus (COVID-19) vs. the flu vs. a cold

Diagnosis

Influenza A

A physical exam is the first step. If the provider identifies common flu signs and symptoms and there is circulating flu activity in the local community, he or she will likely order a test to confirm the diagnosis. Every flu test requires a healthcare provider to swab a patient’s nose or sometimes throat. 

The fastest and most common test is a rapid influenza diagnostic test (RIDT). Results take 10 to 15 minutes, but they might be less accurate than other tests. Plus, RIDTs don’t provide information about the subtypes of influenza A. 

Rapid molecular assays are also common in-office tests. They take slightly longer but are more accurate than some RIDTs in that there is a less chance of a test producing a false negative or false positive. 

If the provider needs more detailed information about the virus’ genetic material and strain, he or she might send the swab to a lab for more in-depth molecular assays that can differentiate influenza A subtypes. 

Novel type A viruses, typically animal-borne, don’t often show up on more basic, commercially available tests. If a provider suspects a novel virus, he or she should discuss the possibility of a reverse transcription-polymerase chain reaction (RT-PCR) test with local and state health departments. Viral culture is also another available test that is generally not used for clinical decision-making, but for a more extensive evaluation of viruses. Culture is most often used for monitoring of potentially novel influenza A or B viruses that might be considered for the next flu season vaccines. 

Influenza B

Like type A, the diagnosis begins with a physical examination, which can sometimes be enough to make a diagnosis. But a test is often necessary for confirmation. 

Even though type B is often a less complex virus, RIDTs are less sensitive to its antigens, so these tests aren’t always accurate. Consequently, a doctor might order a more robust test if they suspect a type B infection. 

Influenza A vs. B diagnosis

Influenza A Influenza B
  • Rapid influenza diagnostic test (RIDT)
  • Rapid molecular assays
  • Viral culture
  • Reverse transcription-polymerase chain reaction (RT-PCR) (if the doctor suspects a novel type A strain)
  • Rapid influenza diagnostic test (RIDT)
  • Rapid molecular assays
  • Viral culture

Treatments

Influenza A

Unfortunately, no treatment will completely eradicate the flu virus. But there are ways to manage its symptoms and reduce its duration. 

Most people simply hunker down with home remedies like lots of fluids, plenty of rest, homemade chicken soup, and pain relievers like ibuprofen (Motrin) and acetaminophen (Tylenol). These are often effective, but only in mitigating flu symptoms. 

For people with influenza A who are part of high-risk groups for complications (children, the elderly, other medical conditions), or who have severe symptoms, healthcare providers might prescribe an antiviral medication like Tamiflu (oseltamivir phosphate), Relenza (zanamivir), or Rapivab (peramivir). These drugs won’t eliminate the virus, but they’ll reduce its ability to attach to cells and further replicate, potentially shortening its duration and preventing further complications. They’re most effective if taken within 48 hours of getting sick.

Influenza B

Type B treatments are nearly identical to type A treatments. The most common response is simply to let the illness run its course while consuming fluids, resting, and taking over-the-counter medications. 

Because influenza B is generally less severe, it might not require antiviral medication, although healthcare providers might still prescribe them for high-risk individuals. 

Influenza A vs. B treatments

Influenza A Influenza B
  • Home remedies (fluids, rest, OTC pain relievers)
  • Prescription antivirals
  • Home remedies (fluids, rest, OTC pain relievers)
  • Prescription antivirals

RELATED: Influenza treatments and medications

Risk factors

Influenza A

Influenza A is unpleasant for the average person. Still, it can be dangerous for seniors (65 or older), children, pregnant women, people with compromised immune systems, or people with a chronic health condition (like heart disease, kidney disease, or asthma). 

Influenza B

Risk factors for type B infections and complications are very similar, although influenza B is more prevalent among children. 

Influenza A vs. B risk factors

Influenza A Influenza B
  • Aged 65 or older
  • Aged 5 or younger
  • Pregnancy
  • Obesity
  • Chronic conditions (asthma, heart disease, kidney disease, etc.)
  • Weakened immune system
  • Aged 65 or older
  • Aged 5 or younger
  • Pregnancy
  • Obesity
  • Chronic conditions (asthma, heart disease, kidney disease, etc.)
  • Weakened immune system

RELATED: Which groups are at high-risk for flu complications?

Prevention

Influenza A

One effective strategy for effective flu prevention (and healthy living in general) is to limit potential exposure. This means washing hands, avoiding extended contact with infected individuals, disinfecting infected surfaces, etc. Anyone who’s already come down with influenza A can help stop its spread by staying home and coughing or sneezing into their elbow. 

Beyond that, the most effective line of defense is the influenza vaccine (flu shot). There are two types. A trivalent vaccine protects against two influenza A strains (H1N1 and H3N2) and one influenza B strain, while a quadrivalent vaccine prevents against those three plus one more type B strain. 

Strains of influenza A (H3N2) can mutate quickly, though, so health officials have to anticipate its evolution every year. As a result, the seasonal flu vaccine can be less effective in preventing type A infections if that prediction is off.

Influenza B

Taking the same general precautions (washing hands, avoiding sick individuals, etc.) effectively prevents type B infection and spread. The flu vaccine is typically a safe bet for influenza B, but it might not always be a perfect match for the annual strain. 

It’s important to dispel a common myth here. Getting a flu shot will not infect someone with influenza A or B. The vaccines contain dead viruses or a single influenza protein, or in the case of the nasal spray vaccine weakened live virus, none of which are enough to infect a human.

How to prevent influenza A vs. B

Influenza A Influenza B
  • Avoiding sick individuals
  • Washing hands
  • Disinfecting surfaces
  • Maintaining healthy eating, sleeping, and exercise habits
  • Seasonal flu vaccine
  • Avoiding sick individuals
  • Washing hands
  • Disinfecting surfaces
  • Maintaining healthy eating, sleeping, and exercise habits
  • Seasonal flu vaccine

When to see a doctor for influenza A or B

A majority of people will ride out the flu from home with only mild-to-moderate symptoms. But sometimes it’s better to visit your healthcare provider. Anyone with one or more of the risk factors for complications listed above should consider seeing a professional to make sure it doesn’t evolve into a more severe disease or respiratory infection. 

A healthcare provider might also be necessary for individuals with severe or prolonged symptoms or other complications like difficulty breathing, chest pain, sudden dizziness, vomiting, neck stiffness, or loss of consciousness.

Frequently asked questions about Influenza A and B

Which is worse: influenza A or influenza B?

Influenza type A and type B are similar, but type A is overall more prevalent, sometimes more severe, and can cause flu epidemics and pandemics. 

Is influenza A virus or bacteria?

Influenza A is a virus, although it may present with similar symptoms of common respiratory bacterial infections, like sinusitis. 

How long does Type A flu last?

Symptoms typically last five to seven days, although they can linger for up to two weeks. Getting a pre-emptive flu shot or taking antiviral medications can help shorten the duration.

How long is influenza A and B contagious?

People with the flu are contagious one day before symptoms develop and five to seven days after that.

Does influenza go away on its own?

In most cases, yes. Generally, it will run its course in seven to 10 days. High-risk individuals (children, the elderly, those with pre-existing conditions, etc.) may need to see a healthcare provider to prevent further flu complications.

Resources