Influenza flu is a contagious respiratory disease caused by influenza virus. You can prevent flu symptoms like fever, chills and sweating through flu vaccine.

Influenza

Online Consultation

Ismail Munir

Overview

During the 15th Century, Italians believed that a liquid flowing from the stars caused disease outbreaks among humans. Hence, they coined the word &#39;influentia&#39;, meaning &#39;to flow into&#39;, to describe a flu-like disease spreading across the country at the time. However, as flu pandemics began to spread across Europe, the English altered the word to influenza.

&nbsp;

Today, the word influenza is used to describe a viral infection of the respiratory system. Also known as flu, it accounts for 3-5 million severe infections and 90,000&ndash;650,000 global deaths annually<a href="#accordion">[1]</a>. The contagious viral infection is caused by influenza viruses such as type A, type B, and type C. These viruses also circulate in animals and can spread to humans, causing outbreaks. Type A and type B cause seasonal flu epidemics every year.&nbsp;

&nbsp;

In Pakistan, influenza type A virus is more prevalent, and mostly peaks during the months of January and February<a href="#accordion">[2]</a>. Although the disease is mostly mild, children under the age of 5, the elderly, and immunocompromised individuals have a higher risk of complications and mortality. Moreover, influenza can often progress to pneumonia, which further increases the risk of death.&nbsp;

 
The seasonal influenza virus commonly causes acute lower respiratory infection in children. A global systematic review conducted in 2018 found that 82% of the in-hospital deaths from influenza virus, in children under 5 years, occurred in low- and lower-middle-income countries<a href="#accordion">[3]</a>. In Pakistan, nearly 20,000 children aged 5-14 years undergo hospitalizations annually due to flu-based symptoms<a href="#accordion">[4]</a>.

&nbsp;

Other than causing the flu in humans, influenza viruses can also infect animals. Humans can get infected when they come in contact with infected animals. There are currently two types of flu strains that can transfer from animals to humans.&nbsp;

&nbsp;

<ul dir="ltr">
	<li>
	<h5 dir="ltr">Avian Influenza (Bird Flu)</h5>
	</li>
</ul>

This is an infectious disease prevalent in birds and is caused by strains of type A influenza virus. H5N1 and H7N9 subtypes of the influenza A virus most commonly cause infections in humans. The virus is transmitted to humans via direct contact with infected birds&#39; saliva, faeces, and mucous. Contact with surfaces or water contaminated with bird droppings is also a mode of transmission. Although humans can contract the disease, transmission from person to person has not been confirmed. Controlling the disease in birds is vital to decreasing the risk to humans.

&nbsp;

<ul dir="ltr">
	<li>
	<h5 dir="ltr">Swine Influenza (Swine Flu) </h5>
	</li>
</ul>

Type A influenza virus (H1N1 strain) can infect pigs, causing a respiratory infection. Influenza viruses that typically cause infections in pigs, don&#39;t commonly infect humans. However, rare cases of crossovers have been reported in the past. Moreover, pigs are susceptible to both human and avian influenza viruses. Hence, they often act as a mixing vessel, re-assorting genes and producing a novel virus that can be transmitted to humans. The H1N1 subtype of the influenza A virus was also a result of this gene assortment, and led to the 2009 swine flu pandemic<a href="#accordion">[5]</a>.

&nbsp;

Signs And Symptoms

The signs and symptoms of influenza can range from mild to severe, depending on the person&#39;s age, overall health, and other risk factors. They typically begin 1-4 days after exposure to an infected person. People are infectious about a day before the onset of symptoms.&nbsp;

 
The common signs and symptoms include: 
&nbsp;

<ul>
	<li>Fever</li>
	<li>Chills and sweating</li>
	<li>Headache</li>
	<li>Runny nose</li>
	<li>Sore throat</li>
	<li>Dry cough</li>
	<li>Shortness of breath</li>
	<li>Fatigue</li>
	<li>Muscle pain</li>
	<li>Vomiting and diarrhea (more common in children)</li>
	<li>Malaise</li>
</ul>

&nbsp;

Causes

Influenza viruses are also found in animals; transmission can occur from poultry or pigs to humans. The most common way of transmission is through direct contact with infected animals, such as during slaughter or in livestock farmers working with animals. However, eating properly cooked meat is not a risk factor.&nbsp;

 
Human-to-human transmission of these viruses occurs through aerosolized droplets from an infected person. These droplets can be produced while talking, coughing, or sneezing. Once a person inhales these aerosols, the virus enters the respiratory tract and starts to cause an infection. Moreover, contact with objects or surfaces contaminated with the respiratory secretions of an infected individual can also transmit the virus. When a person touches a contaminated surface and then touches their mouth, nose, or eyes, the virus gains entry into the body.&nbsp;

 
Although there are 4 main types of influenza viruses (A, B, C, D), influenza only results from infection with three of the viruses. They are all RNA viruses and belong to the family&nbsp;Orthomyxoviridae. The 3 main types are: 
&nbsp;

<ul>
	<li>
	<h5>Influenza Type A Virus</h5>
	</li>
</ul>

Wild birds are the primary hosts of these viruses, but type A virus is also found in humans, pigs, horses, and other animals. The virus can be further classified into subtypes based on the surface proteins haemagglutinin&nbsp;(H) and&nbsp;neuraminidase&nbsp;(N). So far, researchers have identified 18 different H and 11 different N subtypes. Several combinations of these subtypes are currently circulating across the world. However, only H1N1, H1N2, and H3N2 are known to infect humans. The type A virus most commonly causes seasonal flu epidemics. It also causes a more severe infection, especially in the elderly and immunocompromised individuals. 
&nbsp;

<ul>
	<li>
	<h5>Influenza Type B Virus </h5>
	</li>
</ul>

Type B virus primarily infects humans, but has also been found in dogs, pigs, horses, and seals. The virus does not have subtypes but is divided into two distinct lineages - B/Victoria and B/Yamagata. Unlike the influenza A virus, type B does not cause pandemics and causes a milder infection. Moreover, it can only be transmitted from human to human. However, it can also cause seasonal flu epidemics like the influenza type A virus. Current seasonal flu vaccines contain both an influenza A and B virus component.&nbsp; 
&nbsp;

<ul>
	<li>
	<h5>Influenza Type C Virus</h5>
	</li>
</ul>

Similar to the type B virus, influenza type C is mostly found in humans, but it also circulates in dogs, pigs, camels, and cattle. The virus typically causes asymptomatic infections in children. However, mild infections and complications such as pneumonia and gastroenteritis can also occur. There are currently no vaccines against the virus.

&nbsp;

Diagnosis

If a person presents during flu season, diagnosis is usually based on a person&#39;s signs and symptoms. A physical exam might also be conducted to assess the respiratory effects of the infection. However, at times, doctors might conduct various tests to confirm a person&#39;s diagnosis and distinguish it from other respiratory illnesses.&nbsp; 
&nbsp;

<ul>
	<li>Reverse Transcription Polymerase Chain Reaction (RT-PCR) - This is the gold standard for diagnosing influenza. 
	&nbsp;</li>
	<li>Viral Cultures - Cultures are conducted on nasopharyngeal or throat samples. However, results of a culture can take 3-7 days which is often longer than what most people take to recover. Moreover, by then, complications may have developed or it might be too late to start treatment. 
	&nbsp;</li>
	<li>Rapid Influenza Diagnostic Tests (RIDTs) - These detect viral antigens within samples. Although not as accurate as PCR or cultures, these cost-effective tests can give results in 15-20 minutes. However, they cannot determine the type of influenza virus causing the infection. 
	&nbsp;</li>
	<li>Direct Fluorescent Or Immunofluorescent Antibody (DFA/IFA) Tests - This involves using influenza antibodies (labelled with fluorescent) to stain respiratory epithelial cells present in samples. The samples are then analyzed using a fluorescent microscope. These tests can determine whether influenza type A or B is responsible for the infection, but can&#39;t tell the type A subtype.&nbsp;</li>
</ul>

&nbsp;

Treatment

Most cases of influenza are mild or self-limiting. However, in severe infections or those with complications, the doctor may prescribe antiviral drugs. The following treatments are commonly advised for the flu:

&nbsp;

Rest - Doctors recommend rest, plenty of fluids, and a light diet to those suffering from the flu. People are advised to stay at home and wear a mask around others. Moreover, over-the-counter pain relievers such as acetaminophen and ibuprofen can also be used to relieve fever and muscle aches. However, aspirin should be avoided in children with fever as it can increase the risk of Reye&#39;s syndrome.

&nbsp;

Cough Suppressants Or Expectorants - Expectorants can help treat congestive cough by loosening the thick mucus within the respiratory tract. On the other hand, suppressants help relieve cough by blocking the cough reflex.&nbsp;

&nbsp;

Decongestants - These medications help relieve nasal congestion and other symptoms of sinusitis.&nbsp;

&nbsp;

Antiviral Medications - In high-risk individuals and severely ill patients, doctors may prescribe antivirals. These are most effective when given within the first 2 days of symptom onset. There are currently 4 FDA-approved antivirals for treating influenza<a href="#accordion">[6]</a>. These include: 
&nbsp;

<ul>
	<li>Oseltamivir Phosphate - The oral drug works by inhibiting influenza virus neuraminidase (N). This is the spike protein present in the virus and its inhibition prevents viral release and the spread of infection. The drug is currently approved for use in pregnant women and children aged at least 2 weeks and above. Common side effects include nausea, vomiting, headaches, and nosebleeds. 
	&nbsp;</li>
	<li>Zanamivir - This is an inhalable neuraminidase inhibitor and is approved for treating influenza in patients aged 7 years and above. It is contraindicated in people with existing respiratory illnesses such as asthma or COPD. Nausea, vomiting, diarrhea, headaches, and nose irritation are common side effects of the drug. 
	&nbsp;</li>
	<li>Peramivir - The neuraminidase inhibitor is administered intravenously to patients at least 18 years and above. Diarrhea is the most common side effect of the drug.&nbsp; 
	&nbsp;</li>
	<li>Baloxavir - Baloxavir is an enzyme inhibitor that targets viral transcription. The oral pill is recommended for use in people aged 12 years and above. Common side effects include bronchitis, headache, nausea, diarrhea, and common cold.&nbsp; 
	&nbsp;</li>
</ul>

Older antivirals such as amantadine and rimantadine are no longer recommended due to influenza strains developing widespread resistance.

&nbsp;

<h4>"Flu&nbsp; and breathing problems often go hand in hand. Try out our <a href="https://www.merisehat.pk/page/sehat-scan/" target="_blank">sehat scan</a> and check your respiratory rate today."</h4>

Elderly people, immunocompromised individuals, and children are most at risk of developing complications.&nbsp;

 
Pneumonia is the most common complication of influenza. It can either be a primary viral infection or result from a secondary bacterial infection. In people with existing cardiovascular disease, primary pneumonia can occur. It is characterized by rapid progression of the flu symptoms, Thus, resulting in a cough with green or bloody mucus, shortness of breath, and cyanosis. Comparatively, secondary pneumonia typically develops after a short improvement of symptoms. People develop high fevers, cough up greenish sputum, and get chest pains or shortness of breath.&nbsp;

 
Other possible complications of pneumonia include:

<ul>
	<li>Ear infections</li>
	<li>Bronchitis</li>
	<li>Exacerbation of <a href="https://www.merisehat.pk/disease/asthma" style="box-sizing: border-box; color: rgb(0, 123, 255); text-decoration: none; background-color: rgb(255, 255, 255); font-family: -apple-system, BlinkMacSystemFont, &quot;Segoe UI&quot;, Roboto, &quot;Helvetica Neue&quot;, Arial, sans-serif, &quot;Apple Color Emoji&quot;, &quot;Segoe UI Emoji&quot;, &quot;Segoe UI Symbol&quot;; font-size: 16px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 300; letter-spacing: 0.2px; orphans: 2; text-align: left; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px;" target="_blank">asthma</a></li>
	<li>Myocarditis</li>
	<li>Respiratory distress syndrome&nbsp;</li>
	<li><a href="https://www.merisehat.pk/disease/viral-meningitis" target="_blank">Meningitis</a></li>
	<li><a href="https://www.merisehat.pk/disease/encephalitis" target="_blank">Encephalitis&nbsp;</a></li>
	<li>Multi-organ failure&nbsp;</li>
	<li>Sepsis</li>
</ul>

&nbsp;

Influenza is often self-limiting and resolves on its own. However, the following people have a higher risk of developing severe infections and complications: 
&nbsp;

<ul>
	<li>Adults aged older than 65 years, and children less than 5 years of age are more prone to contract seasonal influenza</li>
	<li>People on immunosuppressive medications, suffering from cancer or <a href="https://merisehat.pk/disease/hiv">HIV</a>/<a href="https://www.merisehat.pk/disease/aids" target="_blank">AIDS</a>, and those undergoing cancer treatment have a weak immune system. Thus, putting them at risk of developing complications</li>
	<li>Pregnant women&nbsp;</li>
	<li>People with chronic diseases such as <a href="https://www.merisehat.pk/disease/diabetes-type-1-and-2" target="_blank">diabetes</a>, <a href="https://www.merisehat.pk/disease/asthma" target="_blank">asthma</a>, kidney disease, heart disease, and liver disease</li>
	<li>A body mass index (BMI) of 40 or above increases risk of flu and its complications</li>
	<li>People living in nursing homes or long-term care facilities</li>
</ul>

&nbsp;

The World Health Organization (WHO) recommends the use of influenza vaccines in high-risk groups. This includes healthcare workers, elderly people, immunocompromised individuals, pregnant women, and children. Moreover, the Centres for Disease Control and Prevention (CDC) recommends yearly vaccination for everyone aged 6 months and above for protection against flu and its complications<a href="#accordion">[7]</a>. However, in Pakistan there is no official influenza vaccine policy. A study conducted among parents in Pakistan revealed that only 24% of the study participants were aware of the availability of flu vaccines in Pakistan<a href="#accordion">[8]</a>. Only 6% of the study participants reported vaccinating their child against influenza<a href="#accordion">[8]</a>. Indicating a need for creating awareness about the flu vaccine in Pakistan.&nbsp;&nbsp;

 
Since influenza viruses constantly undergo mutation, a new flu vaccine is developed every year based on the flu strains most common during that year&#39;s flu season. Although the vaccine is not 100% effective, it can significantly reduce one&#39;s disease severity and risk of infection. Research has shown that influenza vaccination causes 26% reduction in ICU admission and 31% reduced risk of death<a href="#accordion">[9]</a>.

 
Also called &#39;flu shots&#39;, the vaccines provide protection against four influenza viruses. They can be administered as an injection or a nasal spray. Influenza vaccines are available as quadrivalent inactivated influenza vaccine [IIV4], recombinant influenza vaccine [RIV4], or&nbsp;live attenuated influenza vaccine (LAIV4). For the 2021-2022 flu season, the quadrivalent vaccine contains influenza A(H1N1) strain, influenza A(H3N2) strain, influenza B/Victoria virus, and influenza B/Yamagata virus<a href="#accordion">[10]</a>.

 
While the flu vaccine is generally recommended for use among everyone, its use is contraindicated in certain individuals. These include: 
&nbsp;

<ul>
	<li>Infants younger than 6 months of age</li>
	<li>People allergic to vaccine components, such as egg proteins</li>
	<li>People who have had a severe allergic reaction to a previous dose of flu vaccine&nbsp;</li>
	<li>People with a history of Guillain-Barr&eacute; Syndrome 
	&nbsp;</li>
</ul>

Similarly, there are certain contraindications to using a nasal spray flu vaccine. The vaccine should not be administered in: 
&nbsp;

<ul>
	<li>Children under 2</li>
	<li>Adults aged 50 years and above</li>
	<li>People with a history of severe allergic reactions to any flu vaccine</li>
	<li>People allergic to any vaccine ingredient, such as egg proteins</li>
	<li>Pregnant women</li>
	<li>Immunocompromised individuals</li>
	<li>People aged 2-17 years that are currently taking aspirin or salicylate-containing medications</li>
	<li>People with a history of <a href="https://www.merisehat.pk/disease/asthma" target="_blank">asthma</a></li>
	<li>People who have recently taken antiviral medications for influenza 
	&nbsp;</li>
</ul>

Other than vaccines, regular hand-washing with soap and water, coughing or sneezing into your elbow, wearing a mask during peak season, and avoiding crowded places, can reduce one&#39;s risk of getting flu. 
&nbsp;

Although flu vaccines are updated every year, they are only effective if the strains in the vaccine match with the ones circulating in the community. However, the rapidly evolving virus results in strains that are different from those selected for the vaccine. As a result, the vaccine is unable to provide adequate protection.&nbsp;

 
Recently, researchers at the National Institute of Allergy and Infectious Diseases (NIAID) have developed a universal candidate - BPL-1357. The vaccine contains four non-infectious avian influenza virus strains. Previously, an animal study of the vaccine had shown a strong immune response in mice exposed to lethal doses of six different flu virus strains, including subtypes not present in the vaccine candidate. Therefore, the team has now commenced Phase 1 human trials for the vaccine[<a href="#accordion">11]</a>. Since the vaccine can also be administered intranasally, the team plans to assess whether it can evoke a mucosal immune response. The trial is expected to end by early next year.

&nbsp;

Due to a similarity of symptoms, it is often difficult to distinguish between the common cold and influenza. However, knowing the differences between the two respiratory illnesses can help one manage their infection better. 
&nbsp;

<h5>Similarities</h5>

<ul>
	<li>Both are viral respiratory infections.</li>
	<li>Common symptoms include runny nose, cough, headache, fatigue, and body aches.</li>
</ul>

<h5> 
Differences</h5>

<ul>
	<li>The common cold progresses slowly, while the flu has a sudden onset.</li>
	<li>Flu symptoms are typically much worse; it includes high fever and extreme fatigue (lasting several weeks).</li>
	<li>Flu is caused by influenza viruses.</li>
	<li>The common cold may result from hundreds of different viruses, more commonly rhinoviruses.</li>
	<li>Flu often results in complications such as <a href="https://www.merisehat.pk/disease/pneumonia" target="_blank">pneumonia</a>, ear infections, sinusitis, and sepsis.</li>
</ul>

&nbsp;

Key Points

<ul>
	<li>Influenza, commonly called flu, can result from three different influenza viruses (type A, type N, and type C). Influenza A and B virus most commonly cause seasonal flu epidemics in humans. These viruses are most commonly transmitted via infected aerosol droplets produced from coughing or sneezing.&nbsp;&nbsp;</li>
	<li>Common symptoms of flu include high fever, headache, dry cough, muscle pain, and severe fatigue that lasts for weeks. In children, diarrhea and vomiting can also occur.</li>
	<li>Although flu is mostly mild, in certain individuals it can lead to complications, such as <a href="https://www.merisehat.pk/disease/pneumonia" target="_blank">pneumonia</a>, ear infections, <a href="https://www.merisehat.pk/disease/viral-meningitis" target="_blank">meningitis</a>, sepsis, and even death.&nbsp;</li>
	<li>Influenza vaccines remain the best preventive measure against respiratory illness. Although the vaccine is not 100% effective, it significantly decreases disease severity in case of infection.</li>
	<li>Influenza is a notifiable disease, and all suspected or confirmed cases should be reported to concerned health authorities.</li>
</ul>

&nbsp;

[1] WHO, 2019. Global influenza strategy 2019-2030, Geneva: World Health Organization.

[2]  Raza, S., Usman, M. & Ahmad, I., 2021. Seasonal trends of Influenza in Islamabad, Pakistan. Journal of Islamabad Medical & Dental College, 10(1).

[3] Wang, X. et al., 2020. Global burden of respiratory infections associated with seasonal influenza in children under 5 years in 2018: a systematic review and modelling study. Lancet Global Health, 8(4), pp. 497-510.

[4] Farrukh, M. J., Ming, L. C., Zaidi, S. T. R. & Khan, T. M., 2017. Barriers and strategies to improve influenza vaccination in Pakistan. Journal of infection and public health, 10(6), pp. 881-883.

[5] Trifonov, V., Khiabanian, H. & Rabadan, R., 2009. Geographic Dependence, Surveillance, and Origins of the 2009 Influenza A (H1N1) Virus. The New England Journal of Medicine, pp. 115-119.

[6] CDC, 2021. What are Flu Antiviral Drugs. [Online]

[7] CDC, 2021. Flu Shot. [Online]

[8] Bukhsh, A. et al., 2018. Parents' attitude, awareness and behaviour towards influenza vaccination in Pakistan. Human vaccines & immunotherapeutics, 14(4), pp. 952-957.

[9] Ferdinands, J. M. et al., 2021. Does influenza vaccination attenuate the severity of breakthrough infections? A narrative review and recommendations for further research. Vaccine, 39(28), pp. 3678-3695.

Trusted By