What Is The Flu
The flu, sometimes referred to as influenza, is a highly contagious illness that primarily affects the respiratory system. It is caused by the influenza virus and is highly volatile, mutating each year through antigenic shift or antigenic drift.
While anyone can catch the flu, the disease is especially dangerous for children under the age of five, immunocompromised individuals, people with underlying medical conditions, and the elderly.
Lesson #: Flu Strain Basics
Okay, we know we’re not all biology majors, so we’re going to take this slow and start from the very beginning. One of the most important things for you to know is that there are four types of influenza viruses: A, B, C, and D. Influenza A and B viruses are the ones we know really well in fact, they’re the ones that cause those almost-annual seasonal epidemics in the United States. Influenza C typically causes a mild respiratory illness and doesn’t typically cause epidemics. Finally, influenza D mostly affects cattle and, at least for now, is not known to infect people. Anyway, more on the specifics strains later.
The second most important thing for you to understand is how these viruses get their names. Influenza A viruses are all characterized based on two proteins on the outer shell of the virus: hemagglutinin and neuraminidase . Say those names ten times fast! These proteins both must be present in order for the virus to replicate, or reproduce. Hemagglutinin helps the virus attach to the cells in your body, and neuraminidase allows the virus to be released from the host cell once it has replicated ultimately spreading the infection.
Phew still with us? Okay, good.
What about those numbers, you ask? Well, they’re determined by the subtype, or secondary type, of hemagglutinin and neuraminidase proteins currently, there are 18 known hemagglutinin subtypes and 11 known neuraminidase subtypes , according to the CDC.2
Safety And Side Effects
The inactivated flu vaccine does not contain the live virus and cannot cause flu. Flu vaccines have a very good safety record. The most commonly reported side effects of flu vaccines are:
- pain, swelling, bruising, hardness or redness at the injection site
- slightly raised temperature
- feeling generally unwell
A higher rate of these common side effects has been reported with Fluad, an adjuvanted trivalent vaccine which was recommended for people aged 65 and over in previous years. This year, Fluad Tetra is being offered to people aged over 65, which also uses an adjuvant. Side effects usually last 1-2 days.
There are several different makes of flu vaccine available each year. For more information on side effects, ask for the Patient Information Leaflet for the vaccine you are offered. Additional information about vaccine side effects, anaphylaxis and adverse reactions can be found here.
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How Do Scientists Choose Which Strains Of The Flu To Include In The Vaccine
With so many strains of the flu virus, you may be wondering how it is possible to get vaccinated against a disease that is constantly changing. In fact, the changing nature of the influenza viruses is the reason why a new flu vaccine is released each year.
Typically, the annual flu vaccine contains three to four strains of the flu that are anticipated to be especially widespread and dangerous in the upcoming flu season this information is published by the World Health Organization and changes each year depending on the spread of various strains.
The vaccine typically includes one strain of influenza A, one strain of influenza A, and one to two strains of influenza B. Flu vaccines do not include strains of influenza C or D, as these types of the virus are not considered dangerous for humans.
Production of the flu vaccine in the northern hemisphere typically begins in February, about eight months prior to the start of the flu season. Scientists use the best available information to carefully select which strains of the flu they anticipate to be highly contagious and dangerous during the upcoming year.
However, the types of flu viruses may mutate over the course of the months in which the vaccine is developed, which can impact how effective the vaccine is in preventing the flu.
Types Of Flus: The 4 Flu Strains Explained
For many people, flu season comes with the threat of a standard virus that comes around every year. The flu, also called influenza, is a contagious respiratory infection caused by a variety of flu viruses. Four different varieties, in fact: A, B, C, and D.
While flu viruses are detected year-round, activity is most common in the fall and winter months often beginning in October and lasting as late as May.
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Should You Get A Flu Vaccine
Although the flu vaccine is not 100 percent effective, there are a number of benefits associated with getting the vaccine, particularly for those who are considered at risk of complications from the flu, such as young children, immunocompromised individuals, pregnant women, the elderly, and people with chronic health conditions.
The flu vaccine can help prevent you from getting sick with the flu in the first place, and if you do get sick, you may experience more mild symptoms and recover more quickly. The flu shot is especially important during the coronavirus pandemic to prevent complications.
Signs And Symptoms In Humans
Avian, swine and other zoonotic influenza infections in humans may cause disease ranging from mild upper respiratory infection to rapid progression to severe pneumonia, acute respiratory distress syndrome, shock and even death. Gastrointestinal symptoms such as nausea, vomiting and diarrhea has been reported more frequently in A infection. Conjunctivitis has also been reported in influenza A. Disease features such as the incubation period, severity of symptoms and clinical outcome varies by the virus causing infection but mainly manifests with respiratory symptoms.
In many patients infected by A or A avian influenza viruses, the disease has an aggressive clinical course. Common initial symptoms are high fever and cough followed by symptoms of lower respiratory tract involvement including dyspnoea or difficulty breathing. Upper respiratory tract symptoms such as sore throat or coryza are less common. Other symptoms such as diarrhea, vomiting, abdominal pain, bleeding from the nose or gums, encephalitis, and chest pain have also been reported in the clinical course of some patients. Complications of infection include severe pneumonia, hypoxemic respiratory failure, multi-organ dysfunction, septic shock, and secondary bacterial and fungal infections. The case fatality rate for A and A subtype virus infections among humans is much higher than that of seasonal influenza infections.
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Side Effects Of The Flu Vaccine
Similar to other types of vaccinations, theres a risk of side effects with the flu shot. Common side effects may include tenderness or redness at the injection site.
In addition, some people experience mild flu-like symptoms for 1 to 2 days after vaccination. This can include weakness, body aches, or a fever, but this isnt the flu.
You might have issues if youre severely allergic to eggs or another ingredient in the vaccine.
Signs of a serious reaction include:
- breathing difficulty
Life threatening allergic reactions are rare after getting the flu shot, though.
Symptoms of a reaction occur within a few hours of vaccination. If you do have symptoms of an allergic reaction, seek immediate medical attention.
The CDC recommends people with an egg allergy still get a flu shot. If you have a severe egg allergy, you may consider getting your flu shot in a medical setting that can treat allergic reactions. You can also request a vaccine that doesnt contain egg protein.
You may have to avoid vaccination if youre allergic to another ingredient in the vaccine.
In rare cases, Guillain-Barré syndrome may develop within days or weeks of a vaccination.
Guillain- Barré syndrome is a neurological disorder where the bodys immune system attacks the peripheral nervous system. This condition can cause muscle weakness and paralysis.
Among those who receive a vaccination, theres only
A Vs B: Severity And Recovery
An uncomplicated infection with either influenza A or influenza B can cause symptoms that last around one week. Some people may still have a cough or feel fatigued after two weeks.
Some influenza A subtypes can cause more severe disease than others. For example, in the recent past influenza A viruses have been associated with more hospitalizations and deaths in children and the elderly than in other age groups, according to the CDC.
In the past, it was thought that infection with influenza A was more severe than infection with influenza B. However, a 2015 study in adults with influenza A and influenza B found they both resulted in similar rates of illness and death.
Additionally, in a Canadian study looking at children 16 years old and younger, influenza B infection was associated with a higher risk for mortality than influenza A.
Influenza C is regarded as the least serious of the three types that humans can get. It typically produces a mild respiratory illness in adults. But theres some evidence that it can cause serious respiratory illness in children under age 2.
The CDC estimates that each year, from 2010 to 2018, influenza infection resulted in between 9.3 and 49 million illnesses, 140,000 to 960,000 hospitalizations, and 12,000 to 79,000 deaths.
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Here’s A Look At The Nature Of The Influenza A Virus Which Causes The Bird Flu As Well As Human Flu Pandemics And Why It Has So Many Variants
Two different subtypes of the bird flu virus or avian influenza, have been detected in Himachal Pradesh the H5N1 avian influenza in migratory water birds at Pong Dam Lake and the H5N8 subtype in dead poultry birds found dumped near the Chandigarh-Solan highway. Heres a look at the nature of the influenza A virus, which causes the bird flu as well as human flu pandemics, and why it has so many variants.
Why Do I Need To Get Vaccinated Every Year
Youve probably noticed by now that we encourage our patients to get vaccinated each year. Why does this particular vaccine need to be administered again, even if you got a flu shot last year? Its because new strains of the virus are constantly appearing and evolving, so the vaccine must change along with them.
Located around the world are influenza surveillance centers that annually monitor the most common strains, collecting data and identifying new and evolving strains. Once the information has been collected, the World Health Organization selects the three strains most likely to circulate during the following flu season. This decision is typically made in February, allowing the development of a new vaccine to begin around midsummer.
Because the three strains change each year, the vaccines are formulated separately before theyre combined into the final product, the trivalent vaccine. While its usually fairly accurate, there have been instances, such as the infamous H1N1 outbreak in 2009, that required the addition of a second, separate vaccination.
In addition to the constantly evolving strains of the flu virus, your bodys immune response changes over time. Taken together, those two factors essentially render the previous years vaccinations useless against new strains. This is why its so important to get yourself vaccinated each and every year, even if you got the vaccine last year!
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How Many Strains Of Covid
A new strain occurs when a virus goes through one or more mutations that change its behavior in some way, but a variant develops when a virus goes through a mutation of any kind, explained Dr. Patricia Couto, an infectious disease physician at Orlando Health in Florida.
According to Lopman, “there are many variants out there,” but a few are concerning because they “appear to be spreading more quickly” and could “possibly the variants that were previously dominant,” he said. The Alpha variant was the dominant variant in the U.S. as of April, according to NBC News.
Here’s a breakdown of the concerning COVID-19 variants, including the Delta variant, and what to know about each:
When A Flu Outbreak Becomes A Pandemic
Seasonal flu – as we are currently experiencing – happens every year and usually peaks in the UK in January and February.
Most people have some immunity to it, having had flu before, or a vaccination.
Those unlucky enough to catch flu may feel very ill, but will normally recover in about a week – although it can be deadly in a small number of cases, particularly among young children and the elderly.
Pandemic flu occurs when a new virus strain emerges from an animal.
Most people have little or no immunity because they have no previous exposure to it, or similar strains.
It affects large parts of the population and spreads across many countries.
Pandemic flu typically affects younger people more than seasonal flu and there is a much higher risk of serious medical complications, hospitalisation and death.
The last time the world suffered pandemic flu was the 2009 swine flu, which spread swiftly across the world, infecting at least 171 countries and killing 457 people in the UK.
Thankfully this was not quite as severe a healthcare crisis as was first feared.
How Do Variants Happen
Coronaviruses have all their genetic material in something called RNA . RNA has some similarities to DNA, but they aren’t the same.
When viruses infect you, they attach to your cells, get inside them, and make copies of their RNA, which helps them spread. If there’s a copying mistake, the RNA gets changed. Scientists call those changes mutations.
These changes happen randomly and by accident. It’s a normal part of what happens to viruses as they multiply and spread.
Because the changes are random, they may make little to no difference in a person’s health. Other times, they may cause disease. For example, one reason you need a flu shot every year is because influenza viruses change from year to year. This year’s flu virus probably isn’t the exact same one that circulated last year.
If a virus has a random change that makes it easier to infect people and it spreads, that variant will become more common.
The bottom line is that all viruses, including coronaviruses, can change over time.
Influenza A And Seasonal Flu
Influenza A is one of the two types of the virus that are responsible for the seasonal epidemics that emerge in the United States nearly every winter. However, of these two types of the virus, only influenza A viruses are associated with global pandemics of the flu.
Flu pandemics occur when a new strain of the influenza A virus emerges that the majority of the population has not been exposed to. When the virus is highly infectious and spreads rapidly among people, a pandemic can occur.
There are different subtypes of influenza A that are classified based on specific proteins on the virus surface: hemagglutinin and neuraminidase . There are different subtypes within the H and N designations, allowing for a possible 198 different combinations of influenza A.
However, only 131 subtypes have been detected in humans to date, including H1N1 and H5N1, both of which have an N1 mutation.
Two of the most common subtypes of influenza A areA, better known as the avian flu, which first emerged in 2009, and A, which was first discovered in 1968.
The A virus that is currently circulating today has mutated slightly, undergoing small genetic changes that allow it to continue to infect people, even when the person has been vaccinated or has already been sick with the virus.
However, the A virus is the most rapidly changing of the influenza A viruses, with many variations circulating simultaneously. This tendency to undergo genetic change is part of what makes influenza A so dangerous.
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Delta Variant From India
This variant is believed to have first emerged in India in October 2020. It’s since spread to the U.S. and currently accounts for more than 6% of sequenced cases in the U.S., Dr. Anthony Fauci said at a recent news briefing. It also has increased transmissibility compared to other variants, according to the World Health Organization.
Who Is Most At Risk
Children under the age of 5 are at high risk of developing flu complications like pneumonia, dehydration, and brain dysfunction.
Influenza is also especially serious for adults 65 and older because of their weaker immune systems.
Other people at high risk of flu complications are pregnant women and those with asthma, diabetes, HIV/AIDS, or cancer.
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Lineages Of Influenza A Viruses
Avian influenza A viruses that infect birds have evolved into distinct genetic lineages based on the geographic locations where they were first detected. These different lineages can be distinguished by studying the genetic make-up of these viruses. For example, avian influenza A viruses that were first detected in birds in Asia can be recognized as genetically different from avian influenza A viruses that were first detected among birds in North America. These broad lineage classifications can be further narrowed by genetic comparisons that allow researchers to group the most closely related viruses together. The host, time period and geographical location are often used in the lineage name to help further delineate one lineage from another.
Avian influenza A viruses are classified into the following two categories: low pathogenicity avian influenza A viruses, and highly pathogenic avian influenza A viruses. The categories refer to molecular characteristics of a virus and the virus ability to cause disease and mortality in chickens in a laboratory setting pdf iconexternal icon. HPAI and LPAI are defined and explained below:
Avian Influenza A Viruses
Avian Influenza A Viruses
Avian Influenza A Viruses
Avian Influenza A Viruses
Avian Influenza A Viruses