INFLUENZA VACCINATION - Frequently asked questions

Who should be vaccinated?
Vaccination is recommended for persons at high risk. This group includes persons aged over 65, immune-compromised individuals (e.g. by HIV infection and steroid treatment), diabetics, adults and children with chronic debilitating diseases (e.g. cardiac, pulmonary and renal diseases). Vaccination is also recommended for individuals who may spread influenza to those at high risk, e.g. medical and nursing staff. Persons with a serious allergy to hen's eggs should not be vaccinated. Vaccination is generally not advised for women in their first trimester of pregnancy and children younger than 6 months.

Why shouldn't everyone be vaccinated?
Persons at low risk (e.g. young healthy adults) do not need to be vaccinated, as influenza is not a serious threat to this group. Targeted vaccination of risk-groups is probably the most cost-effective vaccination strategy.

Why is it recommended that individuals be vaccinated every year?
The antibodies produced in response to influenza vaccination decline over time and may be too low to offer adequate protection for the following year. Also, the influenza viruses continually undergo genetic changes, and immunity acquired because of previous influenza infections or the previous year's vaccination do not necessarily protect against mutated influenza viruses. As the influenza viruses change, the vaccine has to be updated on a yearly basis to include the most current strains.

How does the WHO determine which strains are put into the influenza vaccine?
A global network of laboratories allows the four World Health Organization (WHO) Collaborating Centres on Influenza (Atlanta, London, Melbourne and Tokyo) to identify the viruses circulating around the world. The vaccines are updated annually based on this information so that they include the influenza virus strains that are most likely to cause widespread and severe illness.

What are influenza vaccines made of?
An influenza vaccine normally contains three different kinds of inactivated influenza virus (see below). The viruses are initially grown in fertilized hens' eggs, then killed and purified before being made into the vaccine. Roughly, one egg yields one vaccine dose.

Does the vaccine cause side effects?
Vaccination may cause a local reaction (soreness) at the injection site and, less often, a slight temperature and aching muscles for a couple of days.

How does vaccination protect you?
After vaccination, the immune system starts producing antibodies against the viral proteins from the vaccine strains. If subsequent exposure to the real virus occurs, these antibodies bind the intruding influenza virus particles so that they are eliminated before tissue is damaged; as a consequence people do not become ill or the illness is less severe.

What is the best time to be vaccinated?
It is difficult to plan vaccination campaigns as the beginning of the annual epidemic varies each year. When the vaccination campaign is planned too late, the start of the epidemic may coincide with the campaign and many vaccinees may not have had time to mount an immune response. In the Northern Hemisphere, the best time to be vaccinated is from mid-September to early November.

How effective is the influenza vaccine?
The effectiveness of influenza vaccination depends on the state of the person's immune system, the age of the person being vaccinated, the degree of similarity between viruses in the vaccine and those circulating in the population, the (sub)type of the virus and the length of time from vaccination to exposure to influenza virus. These factors make it difficult to say exactly how effective the influenza vaccine is. Generally, vaccination prevents illness in about 70% of young adults and is less effective in the elderly.

Is it possible to get influenza if you have been vaccinated?
It is possible, particularly among older adults, to become infected after vaccination (see response to previous question). However, for those who are infected after vaccination, the disease is likely to be less severe and is less likely to result in hospitalization or death.

What is the composition of the 2007/2008 vaccine?
The composition of the vaccine for the 2007-2008 influenza season (northern hemisphere) is:
- A/Brisbane/59/2007 (H1N1)-like virus;
- A/Brisbane/10/2007 (H3N2)-like virus;
- B/Florida/4/2006-like virus.

What was the composition of the 2007/2008 vaccine?
The composition of the vaccine for the 2007-2008 influenza season (northern hemisphere) was:

- an A/Solomon Islands/3/2006 (H1N1)-like virus
- an A/Wisconsin/67/2005 (H3N2)-like virusa
- an B/Malaysia/2506/2004-like virus

Candidate vaccine viruses include:
^a A/Wisconsin/67/2005 (H3N2) and A/Hiroshima/52/2005

What was the composition of the 2006/2007 vaccine?
The composition of the vaccine for the 2006-2007 influenza season (northern hemisphere) was:
- an A/New Caledonia/20/99 (H1N1)-like virus
- an A/Wisconsin/67/2005 (H3N2)-like virus^a
- an B/Malaysia/2506/2004-like virus^b

Candidate vaccine viruses include:
^a A/Wisconsin/67/2005 (H3N2) and A/Hiroshima/52/2005
^b B/Malaysia/2506/2004 virus and B/Ohio/1/2005

What was the composition of the 2005/2006 vaccine?
The composition of the vaccine for the 2005-2006 influenza season (northern hemisphere) was:
- A/New Caledonia/20/99 (H1N1)-like strain
- A/California/7/2004 (H3N2)-like strain
- B/Shanghai/361/2002-like strain

What was the composition of the 2004/2005 vaccine?
The composition of the vaccine for the 2004-2005 influenza season (northern hemisphere) was:
- A/NewCaledonia/20/99(H1N1)-like virus
- A/Fuijan/411/2002 (H3N2)-like virus (The currently used vaccine virus is A/Wyoming/3/2003. A/Kumamoto/102/2002 is also available as a vaccine virus)
- B/Shanghai/361/2002-like virus


What was the composition of the 2003/2004 vaccine?
The composition of the 2003-2004 vaccine (northern hemisphere) was:
- A/NewCaledonia/20/99(H1N1)-like virus
- A/Moscow/10/99(H3N2)-like virus (the widely used vaccine strain is A/Panama/2007/99)
- B/HongKong/330/01-like virus

What was the composition of the 2002/2003 vaccine?
The composition of the 2002-2003 vaccine (northern hemisphere) was:
- A/NewCaledonia/20/99(H1N1)-like virus
- A/Moscow/10/99(H3N2)-like virus (the widely used vaccine strain is A/Panama/2007/99)
- B/HongKong/330/01-like virus

What was the composition of the 2001/2002 vaccine?
The composition of the 2001-2002 vaccine (northern hemisphere) was:
- A/New Caledonia/20/99(H1N1)-like virus
- A/Moscow/10/99(H3N2)-like virus (the widely used vaccine strain is A/Panama/2007/99)
- B/Sichuan/379/99-like virus

Does the vaccine protect against the H5N1 virus?
No. Currently available vaccines will not protect against disease caused by the A(H5N1) virus in humans. The WHO and many other organisations worldwide are working towards producing a vaccine against avian influenza A(H5N1). Candidate vaccines have been produced and these are being evaluated in humans. However, mass production of a vaccine will probably not take place unless there is evidence of efficient spread of the A(H5N1) virus between humans.
For more information on avian influenza see http://www.eiss.org/html/faq_h5n1.html.


Last updated: 2 August 2007