Published by Australian Academy of Science
Bird flu – the pandemic clock is ticking Box 4 | Vaccines for pandemics

Vaccination against the flu is, in theory, the best way to prevent a flu pandemic. Usually, vaccines are about 70 per cent effective in preventing the flu. However, there are problems associated with widespread vaccination. Knowing which vaccine to stockpile before the outbreak of a pandemic is a major problem, because you don't know which virus will cause the pandemic. It takes months to make enough vaccine for all potential victims, and flu vaccines only last about 12 months in storage. Every year, companies that make the annual flu vaccine have to throw away expired or unused vaccine, so there is little incentive for them to stockpile. Who pays for the stockpiled vaccine if it isn't used?

There are also some technical problems with making a H5N1 vaccine. H5N1 kills chickens, so the usual way of making a vaccine that relies on chicken eggs doesn't work very well. An alternative genetically engineered virus may need to be used to produce enough vaccine in a short period of time.

When vaccinating, it is usual to have at least two shots, one to prime the immune system and the other to boost immunity. Because of the limited availability of a vaccine, the number of shots might have to be limited to one per person. Even with only one shot, the immune system will respond better to the virus or to another vaccine specifically targeted to the strain causing the pandemic. Adults have some resistance to H1 and H3 type viruses from previous cases of the flu , but have no previous exposure to a H5 virus. Trials to test the effectiveness of a vaccine take some months to complete and assume that the vaccine is effective.

In Australia, with a limited supply of vaccine, not everyone can be vaccinated. If the priority is to minimise the number of deaths, then the aged should receive it. But if you want to keep society running, then priority goes to health care workers and other essential personnel. If the priority is to keep economic losses to a mimimum, then children and working adults should get the vaccine.

The people at greatest risk of infection directly from animals live in Southeast Asia. But individuals and governments are too poor to pay for widespread vaccination in these countries. Decisions need to be made at a global and a local level for effective pandemic control.

Related sites

• Vaccines – how and why? (Access Excellence, USA)

Further reading

• Nature, March 2003, page 6
  Vaccine sought as bird flu infects humans

• Nature, 18 November 2004, page 261
  WHO calls for vaccine boost to prepare for flu pandemic (by Erika Check)

• Nature Medicine, 1 March 2004, page 214
  Race for pandemic flu vaccine rife with hurdles

• New Scientist, 25 March 2005
  US flu vaccine trials may be effort wasted (by Debora MacKenzie)

• New Scientist, 25 February 2005
  Vast budget boost needed to fight bird flu (by Debora MacKenzie)

• New Scientist, 23 September 2004, page 11
  Lack of vaccine raises fears of flu pandemic (by Debora MacKenzie)

• New Scientist, 17 July 2004, page 9
  The superfast way to find cures (by Michael Le Page)

Other boxes

Box 1. An ever-changing virus

Box 2. Past flu pandemics

Box 3. Controlling an outbreak

Box 5. Antivirals bring hope