Influenza (Seasonal Flu)

Influenza, or “the flu,” (flu is short for influenza) is a highly contagious viral infection of the respiratory tract (nose, throat and lungs) that can cause secondary complications. It spreads mostly from person to person and typically around the fall through spring months. There are three types of flu viruses that cause seasonal influenza: A, B, and C and they each evolve and change from year to year.

Influenza A

Usually responsible for the majority of seasonal flu cases. It is found in humans and in animals. Influenza A is spread from person to person by people who are already infected. Touching objects the infected person has touched (doorknobs, faucets, phones) or even being in the same room as the person, especially if they are coughing or sneezing, is enough to become infected yourself. There are many different varieties of influenza A that are classified into subtypes – H and N – and even further into different strains.

H & N Subtypes

H and N subtypes of influenza A are based on the particular proteins that are attached to the virus. There are 16 different types of hemagglutinin (H) proteins and nine different types of neuraminidase (N) proteins. This is how names such as “H1N1” or “H3N2” are acquired.

Influenza B

Type B flu is another type of flu that causes seasonal illness. It is found only in humans. Influenza B has the potential to be very dangerous, but it is typically less severe than influenza A. It does not cause pandemics. Influenza B is typically less severe than influenza A, but it can still be dangerous. There are different strains of influenza B, but they are not sub-typed.

Influenza C

Type C flu, which affects only humans, is much milder than types A and B. It typically causes mild respiratory illnesses and it is not known to have caused any seasonal flu epidemics. Most people who contract influenza C will know that they have some strain of the flu virus because symptoms are similar to those of a cold.

H1N1 – Swine Flu

In the spring of 2009, a new influenza A virus was discovered in Mexico: H1N1, or swine flu. It quickly spread throughout North America, the United States and around the world. H1N1 is a combination of human, swine and bird flu. It became the first flu pandemic the world had seen in more than 40 years.

H5N1 – Bird Flu

H5N1 is the strain of influenza known as bird or avian flu. Typically it is transmitted between birds, but it can be passed from bird to human. It does not spread from person to person. When it does infect humans, bird flu is associated with very serious illness, multi-organ failure, and high death rates. In fact, bird flu has killed more than half of people infected with it.

Who can get the flu?

People of all ages can get the flu. However, children, the elderly, and people with weakened immune systems are most susceptible and more likely to develop serious complications. In rare cases it can be fatal and causes 10,000 to 50,000 deaths a year. For that reason it’s important to prevent it from spreading as much as possible.

The flu is not just a bad cold!

Although they share many of the same symptoms, the cold is caused by a different virus. Flu symptoms tend to develop quickly (usually 1 to 4 days after a person is exposed to the flu virus) and are usually more severe than the typical sneezing and congestion associated with the common cold. The flu is a common cause of problems like sinus or ear infections. It can also cause serious complications like:

  • Pneumonia (lung infection)
  • Worsening of long-term health problems, like asthma or heart failure
  • Inflammation of the brain or heart
  • Sepsis, a life-threatening inflammatory condition

Every year in the U.S., the flu and associated complications lead to more than 200,000 hospitalizations and tens of thousands of deaths.

Do I have the flu?

The most common symptoms of the flu are:

  • sudden appearance of a high fever (100.4º F or more)
  • a persistent, dry cough
  • body aches (especially in the head, lower back and legs)
  • sudden, excessive fatigue
  • tightness of the chest
  • wheezing and congestion
  • diarrhea, nausea, and vomiting
  • chills
  • headache
  • loss of appetite
  • sore throat
  • runny or stuffy nose

In general, flu symptoms can last anywhere from a few days to two weeks.

Flu Vaccine

The seasonal flu shot is a yearly vaccine administered to protect against the flu, or influenza, and are typically available during the peak flu season (August – March).  Although instances of the flu are highest during this period, it can happen any time.

As a general guideline, the CDC recommends that everyone 6 months or older should receive a flu shot. It’s especially important for people who have a high risk of developing complications from the flu to receive the vaccine. This includes:

  • Children aged 6 months to 5 years
  • Adults 65 or older
  • Pregnant women
  • Healthcare providers
  • Nursing home residents

Children younger than 6 months and people with severe allergies to the flu vaccine or any ingredient it contains should not get the flu shot. If you’re uncertain about whether you or someone in your family should get a flu shot, it’s best to talk to your doctor and get a personalized recommendation.

Common symptoms and side effects of the flu shot

The flu shot has, time and again, proven to be the most effective means of preventing the flu. Still, it’s normal to wonder what the symptoms of getting a flu shot are and if it’s worth the risk. Let’s take a look at some of the possible symptoms and side effects of a flu shot.

Common mild symptoms of a flu shot

  • Soreness
  • Headache
  • Fever
  • Muscle aches
  • Nausea

Most of these symptoms will be mild and will go away on their own within a few days.

Rare side effects of a flu shot

  • Difficulty breathing
  • Hives
  • Facial swelling

If you experience any of these, seek medical attention right away.


There are three types of flu viruses: types A, B, and C. Type A tends to be more serious and is likely to mutate into a new strain that people haven’t developed a resistance to. Type B flu viruses are less serious but most often affect young children. Type C causes illnesses similar to a cold.

When it comes to flu season, researchers find that there are nearly always one or two strains of Type A and Type B virus circulating.

In response to the identified strains, there are two common vaccinations available each year:


The quadrivalent flu vaccine is designed to protect against four different flu viruses; two influenza A viruses and two influenza B viruses.

High-Dose Vaccination

Designed specifically for people 65 years and older. Human immune defenses become weaker with age, which places older people at greater risk of severe illness from influenza. Also, ageing decreases the body’s ability to have a good immune response after getting influenza vaccine. A higher dose of antigen in the vaccine is supposed to give older people a better immune response, and therefore, better protection against the flu.

Both quadrivalent and high-dose vaccinations are available here at Northwest Pharmacy.

 *Ask your pharmacist if the flu shot is right for you, especially if you have any egg allergies or past allergic reactions to the influenza vaccine, or have ever had Guillain-Barré Syndrome (GBS).