New flu vaccine protects against all strains including bird flu

Jan 6 2008

A new flu vaccine which protects against all strains of influenza has had promising results in trials.

Researchers say the vaccine's promise of universal protection could help contain a flu pandemic as it protects against all strains of influenza A, the type invariably responsible for pandemics.

B-strains, which are found only in humans, may cause epidemics but have never caused pandemics.

The vaccine apparently has a significant advantage over existing ones in that it does not have to be reformulated each year to match the prevalent strains of flu and it can be produced by cell culture.

It could therefore easily be stockpiled and used as soon as a pandemic strain emerges.

To date results in human volunteers have shown that the Acam-Flu-A vaccine made by Acambis is safe and produces an immune response against a small protein (peptide) called M2e that is found on the surface of all A-strains of the flu virus.

The vaccine was also tested on ferrets, which are often used in flu research because they are susceptible to human and bird flu.

When the ferrets were divided into two groups - vaccinated with the new vaccine or left unvaccinated - after exposure to a large dose of the H5N1 bird flu, all the unvaccinated ferrets died, but 70 per cent of the vaccinated ones survived.

One of the biggest problems with conventional vaccines is that they target parts of the flu virus that can change rapidly.

Every flu season the World Health Organisation identifies the three strains that are circulating, normally two A-strains and one B, and the vaccine is made to order to provide protection against them.

This becomes a race against time, because millions of eggs have to be produced to grow the vaccine and if it is not used it is out of date by the following season.

The Acambis's enterprise identified some aspect of the virus that remains unchanged - a peptide, M2e, on the surface of all A-strains and then developed a vaccine that targeted it.

The vaccine enables the immune system to recognise and be alert to the peptide so that as soon as flu hits, the body’s protective systems swing into action against it.

The vaccine’s effectiveness was enhanced by combining it with adjuvants, chemicals that stimulate the immune system and improve its ability to learn.

The best adjuvant proved to be one called QS-21 which is made by Antigenics, when this was added, 90 per cent of those vaccinated had antibodies against the M2e peptide.

Acambis says if there were an immediate threat of a pandemic flu, it would be possible to complete the trials and market the vaccine within three years, otherwise it will possibly take five years.

Flu viruses notoriously change and mutate and are and unpredictable and changes are more likely to occur when an avian flu strain infects humans, or avian and human strains share genes, as may be happening now in Asia.

Since the H5N1 avian strain first appeared in 2003, it has killed 212 people out of 343 known cases, with most of the deaths in Indonesia, Vietnam, Thailand and Egypt.