What Is Influenza?

Influenza, often called the flu, is a highly contagious respiratory illness that can make you feel miserable. Symptoms include fever, chills, muscle aches, cough, congestion, runny nose, headaches, and fatigue. The flu is notorious for its ability to spread rapidly and cause significant health problems across different populations. But what exactly is behind this troublesome illness?

How Does Influenza Spread?

The flu spreads primarily through droplets made when people with the flu cough, sneeze, or talk. These droplets can land in the mouths or noses of nearby people or possibly be inhaled into the lungs. Influenza viruses can also spread by touching surfaces or objects with the virus on them and touching their mouth, nose, or possibly their eyes. CDC provides comprehensive details on how the flu virus spreads.

What Pathogen Causes Influenza?

The culprit behind influenza is a group of viruses known as the influenza viruses. These viruses belong to the Orthomyxoviridae family. There are four main types of influenza viruses: A, B, C, and D. However, influenza A and B are the primary viruses responsible for seasonal flu epidemics in humans. The other two types, C and D, are less common and less harmful to humans.

What Are Influenza A and B Viruses?

Influenza A viruses are known for their ability to cause severe illness in humans and are often the culprits behind flu pandemics. These viruses are further categorized into subtypes based on the proteins on their surface: hemagglutinin (H) and neuraminidase (N). For example, H1N1 and H3N2 are subtypes of Influenza A. Influenza B viruses, on the other hand, are not divided into subtypes but are classified into two main lineages: B/Yamagata and B/Victoria. Both viruses can cause significant illness and outbreaks, particularly during the flu season.

How Are Flu Strains Named?

The naming of flu strains might initially seem confusing, but it’s a systematic approach. For Influenza A, the strains are named based on their H and N protein types. For instance, H1N1 is a strain with hemagglutinin type 1 and neuraminidase type 1 proteins. Similarly, H3N2 is a strain with hemagglutinin type 3 and neuraminidase type 2 proteins. Influenza B viruses are named according to their lineage, such as B/Victoria or B/Yamagata. WHO offers detailed guidance on flu virus nomenclature.

Why Are Influenza A Viruses More Concerning?

Influenza A viruses are particularly concerning because they have a high potential for causing pandemics. This is due to their ability to undergo antigenic shift. In this process, the virus’s genetic material changes significantly, leading to new strains against which people have little or no immunity. This can result in widespread illness and high mortality rates. In contrast, Influenza B viruses undergo antigenic drift, a more gradual process of genetic change, which makes them less likely to cause pandemics but still able to cause seasonal flu outbreaks.

What Is Antigenic Drift and Shift?

Antigenic drift and shift are two mechanisms by which flu viruses evolve. Antigenic drift refers to small, gradual changes that occur over time as the virus replicates. These changes can lead to new virus strains that the immune system may not recognize, making it easier to spread. On the other hand, an antigenic shift is a sudden, significant change in the influenza A virus, resulting in a new hemagglutinin and neuraminidase protein. This can occur when an animal influenza virus gains the ability to infect humans, potentially leading to a pandemic. You can find more information about these mechanisms on the CDC website.

How Does The Flu Virus Infect The Body?

Once the flu virus enters the body, it targets the cells lining the respiratory tract. The hemagglutinin protein on the virus’s surface binds to sialic acid receptors on the surface of these cells, allowing the virus to enter. Once inside, the virus releases its genetic material, taking over the cell’s machinery to produce more virus particles. These new viruses then exit the cell, often destroying it in the process, and go on to infect other cells in the respiratory tract. This cycle continues, leading to the symptoms of the flu.

What Are The Symptoms Of Influenza?

Influenza symptoms can range from mild to severe, including fever, cough, sore throat, runny or stuffy nose, muscle or body aches, headaches, and fatigue. Some people may also experience vomiting and diarrhea, though this is more common in children than adults. The sudden onset of these symptoms is a hallmark of the flu, making it distinct from other respiratory illnesses like the common cold. You can visit the CDC website for a detailed list of flu symptoms.

How Is Influenza Diagnosed?

Diagnosing influenza typically involves a combination of clinical evaluation and laboratory testing. Healthcare providers may diagnose the flu during flu season based on symptoms and a physical exam. In some cases, particularly for high-risk patients or those with severe symptoms, a rapid influenza diagnostic test (RIDT) or a more accurate molecular test, such as reverse transcription-polymerase chain reaction (RT-PCR), may be used to confirm the diagnosis. These tests can detect the presence of flu viruses in respiratory specimens. More information on flu diagnosis can be found on the CDC website.

How Is Influenza Treated?

Treatment for influenza primarily focuses on relieving symptoms and supporting the body’s immune response. Rest, hydration, and over-the-counter medications for fever and pain can help manage symptoms. In some cases, antiviral drugs such as oseltamivir (Tamiflu), zanamivir (Relenza), and baloxavir marboxil (Xofluza) may be prescribed. These antivirals can shorten the duration of the illness and reduce the risk of complications if taken within the first 48 hours of symptom onset. For more details on flu treatment, visit the CDC website.

Who Is At Risk For Severe Influenza?

Certain groups are at higher risk for severe illness and complications from influenza. These include young children, older adults, pregnant women, and individuals with chronic health conditions such as asthma, diabetes, heart disease, and weakened immune systems. Healthcare workers and caregivers for these high-risk groups are also at increased risk of contracting and spreading the flu. For more information on high-risk groups, check out the CDC website.

How Can Influenza Be Prevented?

Preventing influenza involves a combination of vaccination and good hygiene practices. The annual flu vaccine is the most effective way to protect against the flu. It is recommended for everyone six months and older, with rare exceptions. In addition to vaccination, practicing good hygiene, such as washing hands frequently, covering coughs and sneezes, and avoiding close contact with sick individuals, can help reduce the spread of the flu. For more flu prevention tips, visit the CDC website.

Why Is The Flu Vaccine Important?

The flu vaccine is essential because it helps protect individuals and communities from the flu. It can reduce the risk of flu illness, hospitalization, and death. The vaccine works by stimulating the immune system to produce antibodies against the flu virus, providing protection if exposed. While the vaccine is not 100% effective, it can significantly reduce the severity of illness and the risk of complications. For more information on the importance of the flu vaccine, visit the CDC website.

Can You Get The Flu From The Vaccine?

One common misconception is that the flu vaccine can give you the flu. This is not true. The flu vaccine contains inactivated (killed) viruses or a single gene from the flu virus (in the case of the recombinant flu vaccine), neither of which can cause the flu. Some people may experience mild side effects, such as soreness at the injection site, low-grade fever, or muscle aches, but these are not the same as having the flu. For more information on flu vaccine safety, visit the CDC website.

What Are The Different Types Of Flu Vaccines?

Several types of flu vaccines are available, including the standard dose trivalent and quadrivalent vaccines, high-dose vaccines for older adults, adjuvanted vaccines, and recombinant vaccines. The trivalent vaccines protect against three strains of the flu (two A strains and one B strain), while the quadrivalent vaccines protect against four strains (two A strains and two B strains). The high-dose and adjuvanted vaccines are designed to provide a more robust immune response in older adults. For more information on the different types of flu vaccines, visit the CDC website.

When Should You Get The Flu Vaccine?

The best time to get the flu vaccine is before the flu season begins, typically in the fall. Getting vaccinated by the end of October is recommended, but getting vaccinated later can still provide protection. It takes about two weeks for the body to develop immunity after receiving the vaccine, so getting vaccinated early in the flu season is ideal. For more information on flu vaccination timing, visit the CDC website.

Can You Still Get The Flu After Vaccination?

While the flu vaccine is the most effective way to prevent it, it is not 100% effective. Some people may still get the flu after being vaccinated, but the illness is usually milder and shorter in duration. The vaccine can also reduce the risk of severe complications and hospitalization. For more information on flu vaccine effectiveness, visit the CDC website.

What Is The Role Of Antivirals In Flu Treatment?

Antiviral medications play a crucial role in the treatment of influenza, particularly for high-risk individuals and those with severe symptoms. Antivirals can help reduce the severity and duration of the illness and the risk of complications. They work by inhibiting the replication of the flu virus, preventing it from spreading within the body. For more information on the role of antivirals in flu treatment, visit the CDC website.

How Do Flu Antivirals Work?

Flu antivirals target specific proteins on the flu virus’s surface, preventing it from replicating and spreading within the body. Oseltamivir (Tamiflu) and zanamivir (Relenza) are neuraminidase inhibitors that block releasing new virus particles from infected cells. Baloxavir marboxil (Xofluza) is a polymerase acidic (PA) endonuclease inhibitor that interferes with the virus’s ability to replicate its genetic material. For more information on how flu antivirals work, visit the CDC website.

What Are The Side Effects Of Flu Antivirals?

Flu antivirals are generally well-tolerated but can cause side effects in some people. Common side effects of oseltamivir (Tamiflu) include nausea, vomiting, and headache. Zanamivir (Relenza) can cause throat or nasal irritation, and it is not recommended for people with respiratory conditions like asthma or COPD. Baloxavir marboxil (Xofluza) may cause diarrhea and bronchitis. For more information on the side effects of flu antivirals, visit the CDC website.

How Effective Are Flu Antivirals?

Flu antivirals are most effective within the first 48 hours of symptom onset. They can shorten the duration of illness by about one to two days and reduce the risk of complications such as pneumonia. However, they are not a substitute for the flu vaccine, which is the best way to prevent it. For more information on the effectiveness of flu antivirals, visit the CDC website.

Can You Use Home Remedies For Flu?

While there is no cure for the flu, some home remedies can help alleviate symptoms and make you feel more comfortable. These include staying hydrated, getting plenty of rest, using a humidifier, gargling with salt water, and consuming warm liquids like soup and tea. Over-the-counter medications can also help relieve symptoms like fever, aches, and congestion. For more information on home remedies for flu, visit the CDC website.

What Are The Complications Of Influenza?

Influenza can lead to several complications, especially in high-risk individuals. These complications include pneumonia, bronchitis, sinus infections, and ear infections. The flu can also exacerbate chronic conditions like asthma, heart disease, and diabetes. In severe cases, the flu can lead to hospitalization and even death. For more information on flu complications, visit the CDC website.

How Does Influenza Compare To COVID-19?

While both influenza and COVID-19 are respiratory illnesses caused by viruses, they have significant differences. COVID-19, caused by the SARS-CoV-2 virus, is generally more contagious and can lead to more severe disease and complications than the flu. However, both diseases share similar symptoms and can contract both simultaneously. For more information on the differences between influenza and COVID-19, visit the CDC website.

Can Animals Get Influenza?

Yes, animals can get influenza. Different species, including birds, pigs, and horses, can be infected with various influenza virus strains. Avian influenza (bird flu) and swine influenza (swine flu) are flu viruses that primarily affect animals but can sometimes infect humans. For more information on animal influenza, visit the CDC website.

What Is The History Of Influenza Pandemics?

Influenza pandemics have occurred several times throughout history, with varying degrees of severity. The most notable pandemic was the 1918 Spanish flu, which caused an estimated 50 million deaths worldwide. Other significant flu pandemics include the 1957 Asian flu, the 1968 Hong Kong flu, and the 2009 H1N1 pandemic. For more information on the history of influenza pandemics, visit the CDC website.