Influenza Vaccine (Flu Vaccine)

• What is a flu vaccine?
• How do flu vaccines work?
• What types of flu vaccines are there?
• When is the flu vaccine available?
• Why do I need a flu vaccine every year?
• Who should receive the flu vaccine?
• What are the benefits of having the flu vaccine?
• Is the flu vaccine safe?
  • What about mercury in the vaccine?  

What is a flu vaccine?

Flu vaccines are products that are given to people so that their immune system (which fights off illness) is better able to recognise flu (influenza) infection if the person is exposed, and therefore has a better chance of fighting it off. The flu vaccines that are given to people in Australia are made by killing (known as inactivating) a small amount of flu virus, which is then processed before being injected into the person. Because the virus has been inactivated, there is no way that someone could catch the flu as a direct result of being given the vaccine. This sort of flu vaccine (inactivated influenza virus vaccine) has been used to prevent influenza for over 60 years. The virus has usually been grown in hens’ eggs (before it inactivation), which is why the vaccine may contain tiny amounts of egg proteins. This is the reason that someone who has a severe allergic response to eggs should not have a flu vaccine.  

Each year, new flu vaccines are made so that the tiny proteins on the surface of the virus in the vaccine match the proteins on the flu virus that is spreading that season. The better the vaccine proteins match the ‘flu season’ proteins, the more effectively the vaccine prevents flu related illness. The Australian Influenza Vaccine Committee decides which particles to use for flu vaccines in Australia each year, and they base their decisions from information collected by The World Health Organisation which monitors flu outbreaks around the world.

How do flu vaccines work?

Australian flu vaccines work by exposing the immune system to tiny amounts of the inactivated flu virus. The immune system takes note of small proteins on the surface of the virus within the vaccine, and remembers them. These proteins are known as the haemagglutinin (H) and the neuraminidase (N). Several types of H and N exist, both in vaccines and on the seasonal flu virus itself.  The combination of H and N on the virus changes over time. For example bird flu is H5N1, while swine flu is H1N1.

The body produces its own tiny proteins, called antibodies, which are designed to fight infections. Flu vaccines cause the body to produce specific ‘flu fighting antibodies’, which recognise the surface proteins on the flu virus or flu vaccine. Following vaccination, most adults develop enough antibodies to protect them if they are then exposed to flu infection with the same surface proteins as the ones within the vaccine they received. If the person is then exposed to the flu (e.g. in flu season), the person’s immune system will recognise the small proteins on the surface of the virus (because it was already exposed to the proteins in the vaccine). The person then produces lots of flu specific antibodies, which quickly and strongly fight off the flu infection.

Flu vaccinations may also provide some protection against flu viruses with similar particles as the ones within the vaccine. Some people, such as the very young or very old, or those with poor immune function do not produce as many flu fighting antibodies, so the vaccine may not prevent infection altogether. However, it may prevent complications of influenza, such as pneumonia developing. 

What types of flu vaccine are there?

There are two main types of flu vaccines:

• Vaccines that are used in Australia (purified inactivated influenza virus vaccines), which are made from processed parts of killed influenza virus particles. There are two types of inactivated influenza virus vaccines; split virion vaccines or subunit vaccines. The difference relates to the way the inactivated virus is processed. Subunit and split virion vaccines have the same safety and effectiveness. In the past, whole inactivated viruses were used in vaccines, however some people reacted poorly to these, so they are no longer used in Australia.
• There is another form of influenza vaccine known as the live attenuated intranasal vaccine (LAIV). These have been in use overseas since 2003, but have not yet been licensed in Australia.  LAIV are given by squirting the vaccine into the nose (as a nasal spray), so injection is not required. In years where the surface particles in the vaccine do not match the particles on the virus very well, LAIV is more effective than the inactivated virus vaccine. LAIV is more effective in young children regardless of how well the flu season virus and vaccine particles match. The main side effect from LAIV is mild and short term sore throat and runny nose. After vaccination with LAIV, the person ‘sheds’ influenza virus from their nose and throat, however it is extremely rare that another person would catch influenza from this.

Different companies produce different flu vaccines, which are known by their brand names. Examples of inactivated influenza vaccines available in Australia include:

• Fluvax; (also available as children’s dose)
• Fluad;
• Fluarix; (also available as a children’s dose)
• Fluvirin;
• Influvac;
• Vaxigrip; and
• Vaxigrip Junior.

When is the flu vaccine available?

Influenza vaccination can be given as early as February, but is best given in autumn (March-May) in order to protect against winter influenza outbreaks. Full protection is usually achieved within 10 to 14 days, though it is likely that there is increased immunity (some protection against flu) within a few days. Therefore, even after influenza outbreaks have started, vaccination may still be useful. Influenza vaccination can be safely given at the same time as all routine childhood vaccinations.

Why do I need a flu vaccine every year?

Influenza viruses have a clever way of avoiding human immune systems. Usually, if someone is exposed to an infection, their immune system remembers the infection, so that they do a better job of fighting it off next time the person is exposed. Influenza viruses have tiny proteins on the envelope that surround the influenza virus particles. These are known as the haemagglutinin (H) and the neuraminidase (N). Several types of H and N exist, and the combination of these changes over time. For example, bird flu is H5N1, while swine flu is H1N1. By changing the combinations of H and N, the influenza virus avoids being recognised by the body’s immune system, even if the person has been sick with the flu in the past.

Influenza vaccines are designed to expose individuals to the same H and N combination (known as ‘the strain’) as the flu virus that is spreading that year, so that if they are exposed, their immune system already recognises it and is able to fight it off. For that reason, flu vaccines are mainly only effective for the specific flu virus they were designed to prevent. This is the reason the standard seasonal flu vaccination is not particularly effective in preventing swine flu, which had a new and unexpected combination of H and N. Because the H and N combinations on the flu viruses change constantly, each vaccine is only effective for 12 months, after which time new vaccines need to be created to match the new combinations of H and N on the latest influenza virus causing outbreaks.

If the main strain (H and N combination) of the flu virus remains the same the following year, or only changes a little, low levels of protection from the flu may last longer than 12 months after vaccination. However, a new vaccination every year is recommended to provide ongoing protection against the circulating seasonal flu outbreaks.   

Who should receive the flu vaccine?

In Australia, immunisation is recommended for “any person ≥ 6 months of age who wishes to reduce the likelihood of becoming ill with influenza.” The influenza vaccine is strongly recommended for the following groups of people:

1. People who are at increased risk of complications (such as pneumonia) should they be infected with influenza:

• All adults aged 65 years or older;
• All Aboriginal or Torres Strait Islander people aged 15 years or older;
• People aged 6 months or older with medical conditions that make them at greater risk of developing severe influenza, including:
  • Heart diseases such as cyanotic congenital heart disease, congestive heart failure and coronary artery disease (angina, previous heart attacks)
  • Chronic lung conditions including suppurative lung disease, bronchiectasis, cystic fibrosis, COPD, emphysema, and severe asthma
  • Other chronic diseases requiring hospitalisation or regular medical input within the previous year, including diabetes mellitus, metabolic diseases, chronic renal failure, haemoglobinopathies and poor immunity;
• Chronic neurological conditions that may compromise respiratory function, impair airway clearance, or increase risk of aspiration, including multiple sclerosis, seizure disorders or spinal cord injuries;
  • People whose immunity is poor, including those who require long term steroids, or have HIV infection or malignancy (cancer); and
  • Children aged 6 months to 10 years who require long term aspirin therapy, due to increased risk of Reye syndrome following influenza infection.
• All pregnant women and women planning a pregnancy, particularly those who will be in their second or third trimester during flu season (between June and October);
• Residents of nursing homes and long terms care facilities;
• Homeless individuals, and those providing care to them.

2. People who may transmit influenza to people who are at high risk of complications:

• Staff at nursing homes or long term care facilities;
• Healthcare providers/staff; and
• All household contacts (aged 6 months or older) of individuals in high risk groups.

3. People who are involved in the commercial poultry industry during confirmed avian influenza activity.

4. People who provide essential community services in order to minimise disruption in the event of an influenza outbreak.

5. People who will be travelling in areas where it is flu season, preferably using strains (H and N combinations) that are circulating in that area.

Free flu vaccinations

Free annual flu vaccinations for people over 65 are funded by the Australian government. In Western Australia, flu vaccinations are also free for children aged less than 5 years.

Free influenza vaccinations are provided through Aboriginal Medical Services (AMS), general practitioners and State/Territory immunisation clinics for Indigenous people who are aged over 50, or aged 15-49 and are at high risk. Flu vaccines are recommended for all Aboriginal and Torres Strait Islander people aged 15 years or older, because they are at higher risk of needing to be in hospital, or dying following influenza infection than non-indigenous Australians.  

What are the benefits of having the flu vaccine?

Giving the flu vaccine to people who are at risk of becoming particularly sick from the flu is considered the single most important step in preventing or reducing the spread of flu infections and the deaths that may result from flu infection.

Preventing influenza infection

How effectively the flu vaccine prevents the flu varies according to the age and immune status of the person who receives it, as well has how closely the vaccine proteins (H and N) match the circulating flu proteins. If the ‘match’ or ‘fit’ is good, the vaccination prevents influenza in 50 to 80% of cases. In healthy people under the age of 65, the vaccine has been reported as 70-90% effective if the match is good. If the match is not good, the vaccine is about 50% effective in preventing the flu. This suggests that vaccination is of benefit even during influenza seasons where the circulating strain is poorly matched.

A review study compared nasal spray vaccines (LAIV) to inactivated virus vaccines. It found that the nasal spray vaccine prevented 82% of illness caused by influenza virus infection, while inactivated vaccines (injected) prevented 59% of illness. Both types of vaccine prevented around 30% of illness that felt like the flu (flu-like illness), but was in fact caused by other viruses (such as cold viruses). In this study, the effectiveness of the inactivated vaccine in children aged less than two was no better than placebo.  

For more information, see Tips for Preventing Colds and Flus.

Preventing hospitalisation and complications

Influenza vaccination has been shown to prevent hospitalisation due to pneumonia and influenza in 30-70% of elderly people who do not live in long term care facilities such as nursing homes. For those who do live in such facilities, the vaccine is 50-60% effective in preventing hospitalisation or pneumonia, and 80% effective in preventing death. Although less effective in preventing influenza in care facilities, the vaccine does play a role in preventing severe illness due to influneza, secondary complications (such as pneumonia) and death.

Cost benefits of influenza vaccination

Vaccinating staff against influenza has been shown to be cost effective. Research in America indicates that $58.46 US (around $72 AUD) was saved per staff member vaccinated. Savings are more significant during years of more widespread or severe influenza outbreaks. 10-12% of the workforce (over 50% during pandemics) are absent from work due to influenza in any given year. Influenza infection also causes a financial burden for the people who get sick, and the community in general. Due to the high costs of influenza to individuals, businesses, and the community, use of the flu vaccine to reduce these costs should be seriously considered.

Is the flu vaccine safe?

People should not be given the flu vaccine if they have experienced the following:

• Anaphylaxis following exposure to any of the vaccine ingredients;
• Anaphylaxis following a previous dose of any influenza vaccine; or
• Anaphylactic sensitivity to eggs, including those who develop swelling of lips or tongue, or sudden difficulty breathing or collapse.

Influenza vaccine should be given with caution to:

• People who have developed Guillain-Barré Syndrome (GBS) which started at a time related to previous influenza vaccination. These individuals may be at increased risk of developing the syndrome again following vaccination. However, this risk may be due to the fact that they are more likely to develop GBS simply because they have had it before, not because of the flu vaccine itself. Research conducted in the northern hemisphere from 1992-1994 showed that there was a link between vaccination and GBS. There were 1-2 cases of GBS per million people vaccinated. This relationship has not been reflected in Australian statistics. The risk must be weighed up against the benefits of influenza vaccination for the individual.

Side effects

Side effects associated with influenza vaccination include:

• Local swelling, redness and pain are very common (>10%). This occurs within a few minutes of receiving the vaccine, and may last for hours or for one to two days;
• Fever, a general feeling of being unwell (malaise), and muscle aches are common (1-10%). These tend to commence within a few hours and may last for 1-2 days, and may be more significant in children less than five years of age. These symptoms may be similar to mild influenza infection, however they are not due to having the flu, which is not possible as the flu virus in the vaccine has been inactivated.
• Very rarely, allergic responses in the form of hives, swelling, or anaphylaxis may occur following vaccination. Usually if this response occurs, it will be within seconds or minutes of receiving the vaccination. Urgent medical attention is required.

What about mercury in the vaccine?

There has been some recent concern raised in the media about the presence of mercury in the Panvax swine flu vaccine. This is due to a preservative called thiomersal, which is used to stop bacteria or fungi growing in the vaccine and contaminating it. Thiomersal is used in many medicines where multiple doses are taken from the one container, including Panvax. Thiomersal contains small amounts of mercury. In big enough doses, mercury can cause damage to the central nervous system, kidneys and other organs.

Multi-dose containers were used in Australia to speed up production of the Panvax vaccine so people could be vaccinated quickly during the swine flu outbreak. Preservatives are not required in vaccines delivered from single use containers. In America, multi-dose containers are used to deliver normal seasonal flu vaccine. Thiomersal has been used in medical products and vaccines for more than 60 years. There has been no convincing evidence of it causing any health problems at the low doses used in vaccines, other than minor reactions (redness and swelling) at the site of injection. However, as a precautionary measure, thiomersal was removed from vaccines given to young children in Australia due to the theoretical risk of exposure to mercury. The Australian Technical Advisory Group on Immunisation (ATAGI) has investigated the issue, looking at all the research, and concluded that influenza vaccines containing thiomersal are safe for use in infants, children, adolescents and adults, including pregnant women.

More information

For more information on the common cold and influenza, types of influenza and treatments and tips for preventing influenza, see Cold and Flu.

References

1. The Australian Immunisation Handbook (9th edition) [online]. Canberra, ACT: Australian Government Department of Health and Ageing; 2008 [cited 3 July 2009]. Available from: URL link
2. Couch RB. Seasonal inactivated influenza virus vaccines. Vaccine. 2008;26(Suppl 4):D5-9. [Abstract | Full text]
3. Tosh P, Boyce T, Poland G. Flu myths: Dispelling the myths associated with live attenuated influenza vaccine. Mayo Clin Proc. 2008;83(1):77-84. [Abstract | Full text]
4. Luce BR, Zangwill KM, Palmer CS, et al. Cost-effectiveness analysis of an intranasal influenza vaccine for the prevention of influenza in healthy children. Pediatrics. 2001;108(2):E24. [Abstract | Full text]
5. Ruben FL, Jackson GG. A new subunit influenza vaccine: Acceptability compared with standard vaccines and effect of dose on antigenicity. J Infect Dis. 1972;125(6):656-64. [Abstract | Full text]
6. Nichol K. Efficacy and effectiveness of influenza vaccination. Vaccine. 2008;26(Suppl 4):D17-22. [Abstract | Full text]
7. Influenza (flu) [online]. Canberra, ACT: Australian Government Department of Health and Ageing; 2009 [cited 8 July 2009]. Available from: URL link
8. Childhood flu vaccine campaign [online]. Perth, WA: Government of Western Australia Department of Public Health; 2008 [cited 4 July 2009]. Available from: URL link
9. Immunise Australia: Aboriginal and Torres Strait Islander people [online]. Canberra, ACT: Australian Government Department of Health and Ageing; 2009 [cited 9 July 2009]. Available from: URL link
10. Belongia EA, Kieke BA, Donahue JG, et al. Effectiveness of inactivated influenza vaccines varied substantially with antigenic match from the 2004-2005 season to the 2006-2007 season. J Infect Dis. 2009;199(2):159-67. [Abstract | Full text]
11. Skowronski DM, De Serres G, Dickinson J, et al. Component-specific effectiveness of trivalent influenza vaccine as monitored through a sentinel surveillance network in Canada, 2006-2007. J Infect Dis. 2009;199(2):168-79. [Abstract | Full text]
12. Wilde J, McMillan J, Serwint J, et al. Effectiveness of influenza vaccine in health care professionals: A randomized trial. JAMA. 1999;281(10):908-13. [Abstract | Full text]
13. Bridges CB, Thompson WW, Meltzer MI, et al. Effectiveness and cost-benefit of influenza vaccination of healthy working adults: A randomized controlled trial. JAMA. 2000;284(13):1655-63. [Abstract | Full text]
14. Demicheli V, Rivetti D, Deeks JJ, Jefferson TO. Vaccines for preventing influenza in healthy adults. Cochrane Database Syst Rev. 2004;(3):CD001269. [Abstract | Full text]
15. Jefferson TO, Rivetti D, Di Pietrantonj C, et al. Vaccines for preventing influenza in healthy adults. Cochrane Database Syst Rev. 2007;(2):CD001269. [Abstract | Full text]
16. Jefferson T, Rivetti A, Harnden A, et al. Vaccines for preventing influenza in healthy children. Cochrane Database Syst Rev. 2008;(2):CD004879. [Abstract | Full text]
17. Smith NM, Bresee JS, Shay DK, et al. Prevention and Control of Influenza: Recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR Recomm Rep. 2006;55(RR-10):1-42. [Abstract | Full text]
18. Cohen P, Darling C, Hampson A, et al. Influenza vaccination in an occupational setting: Effectiveness and cost-benefit study. J Occup Health Saf Aust N Z. 2003;19(2):167-82. [Abstract]
19. Grandi P, Franco G. Practising evidence-based occupational health in workers’ groups: How to prevent sickness absence caused by influenza. Occup Med (Lond). 2005;55(1):7-9. [Abstract | Full text]
20. Lawrence G, Boyd I, McIntyre P, Isaacs D. Annual report: Surveillance of adverse events following immunisation in Australia, 2005. Commun Dis Intell. 2006;30(3):319-33. [Abstract | Full text]
21. Demicheli V, Jefferson T, Rivetti D, Deeks J. Prevention and early treatment of influenza in healthy adults. Vaccine. 2000;18(11-12):957-1030. [Abstract]
22. Margolis KL, Poland GA, Nichol KL, et al. Frequency of adverse reactions after influenza vaccination. Am J Med. 1990;88(1):27-30. [Abstract]
23. Thimerosal in vaccines [online]. Rockville, MD; US Food and Drug Administration; 2009 [cited 25 February 2010]. Available from: URL link
24. Australian Government Department of Health and Ageing. ATAGI advice regarding the use of influenza vaccines containing thiomersal [online]. South Melbourne, VIC: Royal Australian College of General Practitioners; 24 September 2009 [cited 25 February 2010]. Available from: URL link
25. Q&As on pandemic vaccine [online]. Canberra, ACT: Australian Government Department of Health and Ageing; 2009 [cited 25 February 2010]. Available from: URL link