Every year in the United States, influenza kills thousands to tens of thousands of people. Probably the best example of how devastating influenza can be was the influenza pandemic in 1918 — this worldwide outbreak killed between 50 and 100 million people in a single influenza season.
The disease
What is influenza?
Commonly known as the flu, influenza is a virus that infects the trachea (windpipe) or bronchi (breathing tubes). Symptoms come on suddenly and include high fever, chills, severe muscle aches and headache. The onset of shaking chills is often so dramatic that many people will remember the exact hour that it started. The virus also causes runny nose and a cough that can last for weeks.
Complications of influenza include severe, and occasionally fatal, pneumonia.
Animals can be infected with influenza
Some diseases are only found in humans; however, influenza can infect many types of animals, such as:
- Birds and poultry, such as chickens and turkeys
- Aquatic birds, such as ducks
- Pigs
- Horses
- Dogs
- Cats
- Sea mammals, such as seals and whales
When animals are infected with different strains of influenza at the same time, a new type can emerge. If the new type can infect humans, be easily passed from one person to another and causes illness, a pandemic, or worldwide epidemic can occur.
What is the difference between an epidemic and a pandemic?
Influenza epidemics occur every year. An epidemic does not affect all people because many people have at least some immunity. On the other hand, when new strains emerge, people do not have immunity, and, therefore, almost everyone is susceptible.
Flu pandemics occur about three times every century. The most recent pandemics have occurred in 1889, 1900, 1918, 1957, 1968, and 2009. The pandemics in 1957 and 1968 each claimed four to six million lives, but the pandemic in 1918 was the most devastating. Between 50 and 100 million people died from the strain of influenza known as “Spanish flu” during that pandemic.
Who should get the influenza vaccine?
The Centers for Disease Control and Prevention (CDC) recommends that everyone 6 months of age and older receive the influenza vaccine each year.
Children 6 months to 8 years of age require two doses of influenza vaccine separated by four weeks if they:
- Have never received an influenza vaccine
- Have not received at least 1 dose of influenza vaccine last year (2015-16 influenza season) or have not received two doses of influenza vaccine since July 2010
- Have an uncertain influenza vaccination history
How is the influenza vaccine made?
All of the vaccines listed below contain either three or four of the influenza strains circulating in the community during a particular year.
One influenza vaccine is made by growing influenza viruses in hen’s eggs, purifying it, and completely killing it with a chemical (formaldehyde). Historically, this influenza shot has been administered into the muscle. However, a newer version of the vaccine, available for adults between 18 and 64 years old, is administered into the skin. Since the newer version uses a much smaller needle, it may be preferred for adults who are apprehensive about getting needles.
Two other influenza vaccines are also given as shots. One is made using recombinant DNA technology, and contains two proteins that reside on the surface of influenza virus. The other is made by growing influenza viruses in mammalian cells (not eggs), and killing it with formaldehyde. Both of these vaccines are advantageous for people who have egg allergies.
The influenza vaccine is unusual in that most years a different vaccine is made. Because strains of influenza virus that circulate in the community can differ from one season to the next, the vaccine must change to best protect against those different strains. Every year in the United States, the Centers for Disease Control and Prevention (CDC) determines what strains of influenza are circulating, and makes sure that all the influenza vaccines that are made that season contain viruses that would protect against the circulating strains. For this reason, the influenza vaccine is probably the hardest vaccine to make.
Do the benefits of the influenza vaccine outweigh the risks?
The influenza vaccine can cause mild side effects. On the other hand, influenza hospitalizes and kills more people in this country than any other vaccine-preventable disease — about 200,000 hospitalizations and thousands to tens of thousands of deaths occur every year. Therefore, the benefits of the influenza vaccine clearly outweigh its risks.
Disease risks
- High fever and chills
- Severe muscle aches
- Headaches
- Pneumonia
- Runny nose and coughing for weeks
- Disease can be fatal
Vaccine risks
- Pain, redness and swelling at the injection site
- Fever or muscle aches
