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Flu vaccine

Alternative Names
flu injection, influenza immunisation, influenza vaccine

The flu vaccine involves the injection of inactivated viruses to protect against influenza, commonly known as the flu.

What is the information for this topic?
There are 3 types of influenza viruses: influenza A, B, and C. Each of these has several subtypes. All of these forms of the virus mutate, or change their genes slightly, so they vary from year to year. That is why a new flu vaccine has to be developed every year. The vaccine is made according to what experts think will be the most common flu viruses to infect people during the following winter. The vaccine has a 60% to 70% success rate in preventing the different types of influenza viruses each year.

It takes about 2 weeks for a person to develop immunity after having a flu injection. The flu season usually begins in April or May and goes through to October or November. The most cases occur in July and September.

The vaccine is recommended for people considered to be at high risk, including the following:
  • people over age 50
  • children and adults with heart disease and lung disease, including asthma
  • people who live in nursing homes or other institutional settings
  • people who have a chronic disease such as diabetes, asthma, anaemia, or kidney disease
  • people who can transmit the flu to others at high risk. This group includes healthcare workers, and employees of facilities that care for people at high risk.
  • women who will be in the second or third trimester of pregnancy during the flu season
  • people whose immune system is weakened because of chemotherapy
  • people with HIV, or AIDS
A recent study showed that the flu vaccine may also be effective in preventing second heart attacks in people who have already had a heart attack. In the study, people who received the flu vaccine had a 67% lower incidence of a second heart attack than the people who were not vaccinated that year.

Elderly individuals who are vaccinated against the flu have a significantly lower incidence of hospitalisation for respiratory disease, congestive heart failure, and death from any cause.

About 25% of adults who receive the flu vaccine report mild soreness at the site of the injection. Young children may develop fever after a flu vaccine. In past years, administration of the flu vaccine was associated with Guillain-Barre syndrome, a rapidly progressive weakness that sometimes causes paralysis. However, this is no longer the case.

There is a risk of an allergic reaction to the vaccine, with possible itching, trouble breathing, or shock. A person who has had this problem in the past should tell the person giving the injection about it. He or she may decide not to administer the vaccine in order to avoid the chance of a repeat reaction.

Individuals who should not get flu injections include the following: A nasal vaccine for the flu is being tested and may soon be available.

A person who develops a high fever (a temperature above 38 degrees Celsius) or an allergic reaction after the injection should call their doctor. The doctor can also discuss other questions or concerns about flu injections.

Author: James Broomfield, MD
Reviewer: HealthAnswers Australia Medical Review Panel
Editor: Dr David Taylor, Chief Medical Officer HealthAnswers Australia
Last Updated: 1/10/2001
Potential conflict of interest information for reviewers available on request

This website and article is not a substitute for independent professional advice. Nothing contained in this website is intended to be used as medical advice and it is not intended to be used to diagnose, treat, cure or prevent any disease, nor should it be used for therapeutic purposes or as a substitute for your own health professional's advice.  All Health and any associated parties do not accept any liability for any injury, loss or damage incurred by use of or reliance on the information.


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